~osttrgery,
,~ : ~
~
~
"
when theparaes~esias
?i:i~:ii!iCi(ii?L iii!5 ¸ ?i~
:
~:
. . . .
~tanted onthe is pain almost ~ificant as was ~i~e implantation occurred bilaterally also to one side, The eharagesof thresholds generally
i i i i ii i iiii!~i iii~!iiiiiiiiilliiI iii iiiiiii
258 TABLE I
i
i~
RESULTS OF DORSAL COLUMN STIMULATION
Case
Age
C~rus,"of pain
Duration of pain (years)
1
47
2
55
3
40
4
62
5
58
6
52
7 8
43 66
Spinal trauma 3 Paraplegia Spinal trauma 3 Paraplegia Pc~stsurg. 3 Thoracotomy Pc,stsurg. 6 Pyelotomy Pcstsurg. 2 Pyelotomy Brach. plex. trauma 18 Phantom Sciatic 13 Sciatic 12
9
42
Sciatic
27
10
52
Sciatic
10
Previous treatment for pain Myelotomy Symp. block Acopuncture Local vibration Neurotomy Nerve block Nerve block
Sympathectomy Disc surgery Disc surgery Cordotomy~ Disc surger '~ Spinal fusion Disc surgery
Folloiv up Pain relief (moJ~ths) i
3
None*
17
Complete
20
Complete
10
Complete
3
Complete
6
Complete**
23 16
Complete Partial
12
None
14
Partial
* Electrode removed. ** Receiver temporarily removed due to infi.~ction along cable.
DCS has primarily been assumed to inhibit the discharge in small pain fibres segmentally in the dorsal horn by activity descending in the dorsal column fibres 10. It has also been fbund that similar mechanisms for pain inhibition may be: active on a supraspinal levelg,21. In some cases with localized pain, relief may be achieved by electrical[ stimulation of the appropriate peripheral nerve trunk15, zS. During the stimulation the area supplied by the stimulated nerve is oftea found to be analgetic. These effects have been ~nterpreted as being the result of activation of the spinal pain gate. Opposing this view, it has recently been claimed that the analgesia induced by peripheral nerve stimulation is caused by block of AO fibres 5. In these experiments it was. also shown ~that in the analgetic area the threshold for touch was markedly raised. According to a recent report changes irL the sensory perception may also be found during DCS1L Otherwi,se, the patients' ability to perceive cutaneous sensation such as touch, vibration and proprioception has been reported to be hrgely unaffected during such stimutat!on. Not until the intensity of the stimuli was increased to almost intolerable '~evels were there any s~gns of elevation of the sensory thresholds TM. Pain sensation as tested with pin-prick does not seem to be ~dtered by DCS ~9 but when tested with electrical stimulation of the skin the thresheld may be considerably raised ~4. It has also been observed that the sensation of deep pain as provoked by Achilles tendon pinch is sometimes altered and felt as touch onlyz3.
259
Fig, 1. P a t i e m (case 3) with causalgia after left-sided thoracotomy (scar indicated by a crossed line in the lower, left thorax). Antenna for external electrical stimulation attached over receiver in right subclavicular region. Solid line delimits the area with pain and hyperaesthesia, and dotted lines denote the 4 trunk locations where pain thresholds were measured: one close to the scar~ two ad° jacent to the pain area (1) (2), and one contralaterally (3) to the pain area.
The aim of the present study was to investigate, with quantitative methods, the effect o f DCS on the thresholds of touch, vibration and cutaneous pain. The experiments were designed also to look for a correlation between the effect of DCS on spontaneous pain a n d o n t h e various sensory thresholds. The establishment of such a relationship would be of value for the objective evaluation of DCS for treatmem of pain. CL1NrICAL MATERIAL AND METHODS
Material The material consisted of i0 patients undergoing treatment with dorsal column stimulation. As listed, in Table I various conditions of benign, chronic pain were represented. The histories of pain amc anted to a maximum of 27 years, tn 9 patients the dorsal column electrode was implanted at a high thoracic level, slightly dislocated towards the side of the pain, and in one patient (case 6) at a cervical level. With ~he equipment used (Medtronic) the spinal cord is stimulated monopolarly. In 5 cases
• 260
ii ii i:
i) ii!ill ii ~I~!:~I~ ii!ii~i~ili~i~~i ....
(cases 1, 2, 3, 7, 8), the spinal electrode was placed subdurally with the arachn0id left intact, and in the remaining patients layers, was used. The receiver was placed subcutaneously in (see Fig. 1). Prior stimulation applie~ ma~:imal pain. A c, in 8 of the patients patients percutaneous dorsal column stimulation was puncture of the spinal canal with a blunt electrode and during this procedure apartial relief of pain ~as reported. In another patient, DCS was achieved semi-permanent electrode by which a complete alleviation of the pain was achieved, There were no immediate surgical complications but several of the patients experienced a severe, radieular pain located in the thorax at the level of the implant and lasting for about a month postoperatively. In two of the: patients deeubitus appeared about 2 months postoperatively over a short distance of the electrode cable. Presumably, this was caused by tunneling the cable too superficially under the skin, In one of these patients the equipment was remo~ ed since n o positive effect of t h e stimulation had been obtained (case 1). There were no visible changes of the spinal cord h t the electrode plate was c:overed by a thick deposit of fibrous tissue, In the other patient (ease 6), there were a!lso local signs of infection and the receiver and part of the ~:able had to be tempora::ily removed. " h e general results of D,CS were as follows" 6 patients obtained a complete relief cf pain; 2 had a partial relk.f and 2 had no beneficial effect of the stimulation. The o~.3servation time is at present (April 1975) 3-23 months. The 2 patients who are classified as having a partial pain relief initially experienced a good alleviation of pain but the effect decreased 2-4 months postoperatively. These 2 patients are now using transcutaneous stimulation together wi th the DCS and with this combined stimulation they have obtaineda fairly satisfactory relief of pain, For the present st udy, 5 patients were selected who represented different types of pain and were observant and well cooperative in tedious psychophysieal testing (cases 3, 4, 6, 7 and 9 in Tab',~ I). Several months had elapsed after the electrode implantation so that the patients had become fully acquainted with the use of the stimulator and were in a . ,.~ady-state condition, The patients were hospitalJized a n....d subjected to repea~:d testing and close ob.,ervation during at least 3-6 days as regards the prevalence and intensity of pain in relation to the DCS, During the testing sessions the patients were instructed to use the dorsal column stimulators according to a strict time-table which permitted the ~:esting to be performed both when the patients were in a s;tate of maximal spontaneous pain and when being free of pain after an adequate period of DCS. i
6 c ,~
Case .-'~was a 40-yea~,old man with eausalgic pain in the lower part of the left ~hora× (appro~:. Th7-Th10) following a trans-thoracic vagotomy performed 3 years earlier. Because of the pain the seventh iatercostal nerve had been resected but the pain became worse. Anaesthetic block of the tenth intercostal nerve had a beneficial effect and the nerve was therefore~,a s a trhl, exposed and subjected to beta-h'radiafio:n. Following this. the patient experienceda short-lasting, partial pain reAief.
26t ;d but with no effect on the pain. :wo types, one superficial, burning rper- and dysaesthesia for touch, ~termatomes (Fig. 1). Transcutaneous stimulation of the dysaesthetic area resulted in a marked retraction of the Lnd the transevel of 40 Hz tur~ed Case 4 was a 62,year, old woman who since 6 years had suffered from a causalgic pain located in the right waist ,and the groin region following repeated operations for nephrolithiasis. Intercostal nerve~ block ihad be~n tried several times but with a transitory beneficial effect ordy. The patient had a very high comumption of analgetics, both narcotic and non-narcotic. With transcutaneous stimulation applied to the painful area the patient experienced good pain relief but this treatment had to be discontinued due to locaJ irritation of the skin. DCS with 25 Hz and 0.2 msec pulse duration resulted in an almost complete relief of pain and the patient was able to do without narcotic analgetics. Periods of stimulation have decreased )r was used once or twice a day. Upon patient, as well as another in the series nephro- and uretherolithiasis and this,
:affic accident bad a complete evulsion of his right brachial plexus, Since then the arm remained totally denervated and despite of the lack of motility and sensibility the patient has refrained from having his arm amputated. There had been a persisting and severe burning pain which was perceived in the hand and the forearm. In addition, there were attacks of stabbing ache which were almost unbearable. Despite of the pain the patient had been able to maintain his work as a truck driver except for limited periods. Consumption of non-narcotk's was initially very high but has decreased over the years. Two years after: the accident a cervical sympathectomy was performed but with no benefit to ~.hepatient. Transcutaneous stimulation applied to the brachial plexus considerably reduced the pain but there was local irritation of the skin. Therefore, it was decided to perform a dorsal column implant. The spilml electrode was placed at the C4 ~evel and stimulation caused l:,araesthesias to be felt in the right arm only. Stimulation resulted in an almost complete abolition of the pain. Optimal frequency was 100 Hz with a pulse duration
sensory modalities were highly defi:zient in the foot and on the lateral and dorsal aspect of the lower ~eg.
lied on the leg caused a partial relief of pain. Surprisingly, the brachium the effect was equally or even more pronouncegs and there was a total abolition of pain. Optimal stimulus frequency had dropped from an initial value of about 80 V~z to about 30 Hz. The stimulus pulse duration was kept at 0.3 msec. At the time of the study, the patient was free of analgetic drugs and had resumed work for the first tirae since t960., Case 9 was a 42-year-old woman who s~.ffered from low back, sciatic pain since l9 years of age. She had underwent disc surgery 4 times including a fusion owration 5 years before admittance. The chronic back pain had becomeverysevere during the last years and the patient had become more and more disabled. She Was very dependent upon excessively high doses of non-narcotic anatgetics as well as on tranquillizers. There was a slight paresis of the right leg and reduced sertsitivity to vibratory stimulation in the left foot but o~herwise there were no obvious neurologicai deficks. Trans-
262 cutaneous sfimu!atio~ of ~:he dorsal column pain and therefore a felt to invade the pai any effect on the paiJ of time with varyint trials were given up a . . . . . . . . . . . . . pain which confines her to bed most of the day.
Methods The pain threshold was tested by a pair of flat forceps by which a fold of skin was pinched manually with increasing pressure until the subject reported pain. The forceps had a symmetrical rectangular contact area of 10 sq. mm z with blunted margins to avoid incMve violence of the skin. The pressure was recorded by means of a strain gauge the output of which was calibrated in g/sq.mm. The tactile threshold was tested according to Lindblom ~4 by half cycle sinusoidal mechanical pulses applied through a 2 mm diameter blunt probe. The threshold amplitude, expressed in #m, was determined by the method of limits, i.e., the stimulus strength was succe,si'~ly increased with notation of the value when the subject perceived the pulse and then decreased with notation of the value when the sensation disappeared. The mean of the two readings was usually used to denote the threshold. The vibration threshold wa.s determined by applying a 100 Hzsine wave stimulus from an electromagnetic biothesiometer (Bio-Niedical Instr. Inc., Chagrin Falls, Ohio). The stimulator head consisted of a 6 mm diameter plastic probe, with rounded edge. An accelerome~:er was mounted on the shaft of the stimulator, the movement of which was displayed on an oscillo.~cope and calibrated in ~m peak to peak. The stimulator was applied with the l~ressure ef its own weight (440 g) and with the moving shaft in a position which was as near to ~ertical as possible and at the same time perpendicular to ~he skin surface. Care was taken to apply the stimulator to the underlying bone by pllacing tion gave the least var~ati~ . . . . . . . . . . . . . . . . . . . _ ....... .. determined with the method of limits. A full description of the melhod including normal threshold values for commonly used stimulus sites such as the metatarsal and metacarpal regions is in preparation s . RESULTS
The patients had developed a somewhat different routine for the use of the dorsal column stimulator dependent on the type o1' pain and the effect of the stimulation. Thus, for instance, in case 7 the pain was largely tolerable during daytime as long as the patient couldwalk around or move the leg freely. Stimulation was mostly performed during the night when the pain was severe. Switching on the stimulator caused the pain to vanish after 3-6 min. After this period, the voltage was stightly decreased, as guided by the intensity of paraesthesias and b y t h e pafiem's experience of the stimulus intensity required to withhold the pain. If the stimulator was left on the patient could sleep all night and awoke painless. In other cases the ~timutator was
:263
A
B
C
D
E
), in intact and ffore and after r,S1 and Sz, respectively). A befoie, B and D im. The pain threshold (26 g/sq.mm) obtained in location 13 on the trunk (see Fig. 1) was chosen as reference and given the index 100~. Hyphens indicate S.E.M.
F
only used for short periods of? time. In case 3 stimulation for 10 rain was enough abolish the pain for 5 h. The pain-free period had successively increased from 0o~ initially after the operation. During the sessions of sensory testing it was repeatedly confirmed that stimt~ao tion with optimal stimulus parameters caused a reduction of the spontaneous pain
and " ined or stronger stimulation was not tolerated. The was the same in all patients in that they were never felt above the level of the spinal e!ectrode and that the spread in caudal direction primarily occurred ipsilaterally to the side of the pain which was also the side to which the implanted electrode had been slightly shifted° In cases 4 and 7 paraesthesias also appeared in the contralateraI trunk and leg when high stimulus voltages were used tcases3and 9there was no contralateral spread even with the Nghest toleraNe v in the p w i t h the cervical implant (case 6) the paresthesias did not spre~ nd theipsitateral arm and pectoral region. DCSat s s strengths which were subliminal for the provocation of par-
264 pm
/
30o
111 o
-J o~
200
z tIJ od
o=
m
I00
0
o
½
1
~½
2
2½
3h
TIME
Fig. 3. Effect of dorsal column stimulation of different intensities (Sz-S4) on the tactile threshold of the right (unaffected) foot sole in case 7. Sz and S2 were sublimina:. 88 optimal and $4 supraoptimal for suppression of pain. Hatching denotes the presence of paxaesthesias. Note low threshold values during Sz, transitory elevation during S2, intermittent elevati, Jn during S8 and consistent elevation during $4. Spontaneous pain, as shown in the bottom of the diagram, was slowly reduced to about 50 70 during $2 and during the initial part of Sa it was rapid!~' and completely abolished.
aesthesias could some'times reduce but never abolish the pain. The thresholds for induced cutaneous pain were generally not significantly influenced by DCS of neither subliminal nor supraliminal intensity. However, there wa,; one exception to this finding. In case 3, some undis threshold when tested within These findings are illustratec the pain area (black columns) was significantly lower than that found in the homologous contralateral area (position 3 in Fig. 1). The thresho! area amounted to 26 g/sq.mm and was arbitrarily given the ir~ ~ngs from this and other trunk positions with normal skin and those from the hands and feet constituted t w o separate sets of data, representing different threshold levels which were all well within normal limits. These da~a were treated as two groups and are represented by hatched and unfilled colum:cs respectively in Fig. 2. The first stimulation (81) was of optimal intensity for the suppression of spontaneous pain and of 3 rain duration. As appears (B), the thresholds of normal skin areas were largely unchanged whe,'eas- that of the hyperpathic pain area h a d risen t o approxi' mately the same normal level as ttae rest of the trunk. Subjectively, the superficial hyperpathic pain had disappeared as well as the hyperaesthesia to touch, ~ i c h now appeared ncrmat on testing with cotton wool. Also the sensation to pinprick and cold and war:nth had lost its unpleasant character. This was lmain~ained
condition
!~ !!i~)~ -~ ~i i¸ 265 Lift3
!
mn
A. ¸
B ~i!)iii!::iiiiii;iiiiiil
:iiiiiiiiiiiiiiiiiii a ii!iiiiii!ii!iiiiiii! , ~
!iiii!i!iiiiiiiii
~
a
............ .....-...........:+:. +:.:.:
C
12'
0J
r 0
~ 2 0 - 2 5 Hz
~O-50Hz
100Hz
200Hz
Fig. 5. Effect on vibratory threshold of dorsal colum)t stimulation at different intensifies (A, B, C) and frequencies (20-25 Hz, 40-50 Hz, 200 Hz). Filled and empty circles mark 'yes' and'no' responses of tlu'eshold sensation, the difference being the threshold gap. Each point represents the mean of two consecutive measurements made within l rain. Stimulation of metatarsal region. Intensities of DCS: in A producing paraesthesias (pointed area) only in the midthoradc pain area, in B cauda!ily to the foot, in C with the same dis,tribution but stronger. Periods during which DC$ was performed indicated by black bars. Note slight threshold increase during DCS in B, and marked increase during and after DCS in C.
disclose a residual poststimulatory elevation of thresholds for vibration similarly to what was found for touch. In Fig. 5 is illustrated the effi~ct of DCfi of different intens,ifies and frequencies on the vibratory threshold tested in the left metatarsal region in one of the patients. A, B and C rewesent three settings of the DCS voltage, viz. subliminN [A), liminal (B) and suprah~J~mal (C) for paraestheslas m the foot. In .~hls tagure be~N yes an °no' values (see 5{ethods) havi been plotted to illustrate also the effect on the 'thresh, old gap'. It appears that DCS caused an increase of the threshold which was related to the stimulus voltage. There was a]so a considerable increase in the threshold:gap which was most prominent with high stimulus voltage (C). Generally it was not
the D C S o n ~ h e thresholds I~orany type of peripheral stimuli used. DISCUSSION
stimulus implant. replanted the dura esias was , impulse discharge evoked in the dorsal columns and transmitted centripetally via the dorsal column nuclei or centrifugally via segmental dorsN horn collaterals to other ascending tracts such as the spinothalamic1°. It is less likely that the paraesthesias were the results of direct activ~Iion of other pathways than the dorsal column. With the stimulus intensities used in the present study there were no motor responses or sensa-
-
evoked by DCS 18. It is, ne~ssary "go consider the possibility that distraction caused by the spontaneoUslpaJ:nor by the paraesthesiaS during DCS influenced the perception of" ~ e per!pheralsensory stim~ali. This ~s im!ikely for several reasons. The thresholds were ~n no way four~d to be related to the presence er absence of sponta~eou~ palm E~en intensive 'paraestlheSiasin the trunk or legs &d never mgmficantty influence ~ e t L r ~ olds meas~edi ~n'the arms, i.e:, above the level of the spinal etectrede~ The paraes°
268
the~ias disapp -a~ed . . immediately . . . upon. cessation of DCS whereas elevation ~ of: the threshoAs often persisted for some minutes. It can therefore be concluded ~Lhatthe elevation of thresholds was independent of distraction but the result of Stimulation of the dorsal co|utah. In the patients who obtained pain relief :by DCS an elevation 0 f l t h e ~ ¢ s h o ! d S ~ for touch and vibration was consis'tenfly observed belov,(the !e~el:ofthe)spinaI:6le~L~ trode. In contrast, th,,-normal cutaneous thresholds for induced:pain ~ere : , ~n6t ,- itF fluenced. It could be assumed that DCS initiates antidromic impulse discharges ]n fibres mediating touch and vibration and that these discharges collide with thenaturhl orthodromic activity set up by the peripheral stimulation. A collision might occur at any level between tlhe spinal electrode and the peripheral receptor. Anfidromic •impulses may also invade the receptors and reduce their responfivenesslz. An elevation of the sensory thresholds (au~ed by antidromlc discharge :in the primary afferent fibres would be related to the frequency of the DCS. In large cutaneous afferents, the conduction time from the s )inal electrode to the terminals in the foot ma, f be estimated to about 40 msec. The trar smission of the orthodromic impulses from the periphery to the frst segmental relay would require the afferent pathways to be available "~ for a similar period of time. This would imply that dorsal column stimuli applied with intervals of 80 msec, i.e., with a frequency of 12.5 iHz, should cause a partial block unless the DCS and the peripheral stimulation were extremely well timed. At a DC$ frequency of 25 Hz m,. ..... activated dorsal column neurones would be totally blocked for the transmission of impulses 3et up by the peripheral stimulation. The results did not reveal such a frequency-dependent relationship. It is therefore not probable that antidromic blocking is the primary mechanism behind the elevation of sensory thresholds observed during DCS. Besides, the poststimulatory elevation could hardly be explained in terms of such a simple mechanism. Local cl~anges in the cord induced at the ,rite of stimulation12 might interfere with the transmission of touch and vibration and thus to.use a :threshold elevation. A further explanation would be that occlusion occurs in the first synaptilc reiay ~inthe DC nuclei or segmentally in the dorsal horn as a result of impulses descending -,0: antidromically to the segmental collaterals. The explanations given above would imply that the perception of touch and vibration is normally mediated via the dorsal column. This is a much debated question ~,~'5, According to recent experimental data the dorsal column is essential for sensory detection thresholds~L However~ the present results cannot be taken as evidence that this is the case. DCS m~ght interfere with the tested mechanoreceptive functions by way of convergence at a supraspmat le ~/el, whxch may account for m, hibitory effectsL Specific inhibitory systems may al.~o be activated by DC$. Thus, it has been e×perimentally shown that such sfimuhtion may impose an inhibitory effect o n the c~orsat horn units responding to both A - a n d C-fibre input~,9,1oi ~nhibifion may also occur via a supraspina] loop involving the dorsal column nuclei and controlling the inp~at to the spinocervical tract 4. This type of supraspinal iinhibit0ry control has also been shown to be e×erted contralateratly, whichmay be of relevance for the present finding of threshold elevation ~:ontralateral to the DCS
269 Lac~ or effect or v b ~ on m o u c e a cutaneous wa*~tested in an area of dysaesthesia in one
pain. Together with alleviation of pain, D C S caused elevation of thresholds for vibration and touch in all cases except for the one in which stimulation was inefficient for pain relief. Th;s observation may indicate the possibility that the same blocking of pain and in the effects on sensory
ACKNOWLEDGEMENTS
The study was supported by grants from Karolinska Insfitutet and fl'om the Swedish Medical Research Council (B75-14X-4505..01).
REFERENCES 1 Albe-Fe:~sard, D., and Besson, Y. M., Convergent thalamic and cortical projections
the nor,.is~r
in by ol. ~eia. en
Press, New York, 1974;pp, 749-754: 7 Fox. J2 L. Dorsal column stimulation for relief of intractable pain" problems en.countered with in terms of displacement amplitude. Iggo, A., and Zimmermann. M~; ~gmental and supraspinat acfiens on noxious and non-noxious skin stimuli, Pain, 1 (1975) 14%t65. 10 excitary factors influencing receptive fields of lamina 4spinal cord cells, Exp, BrainRes., 9 (1969) 284-306,
physioL stand,, 44, Supp!, 153 (!958)1.84; !5
........
..............
amplitude
16 Melzack,
and Wall, P. D,, Pain mechanism:
:new
17 Myers, BouraSsal C, and SW t . Brain Res., 70 (1974) :350--355. 18 Nashold, B.' Somjen' i3., ~ and Friedman, H;, tion of the dorsal funiculi in man, Exp, Nekrol.; 36 (1972) 273~287' 19 Nashotd, B. S., Jr., and Friedman, H,, Dorsal column stimulation for control of pain, Preliminary report on 30 Fatients, d. Neuresurg., 36 (1972) 590-597. 20 Noordenbos, W., Pail:, Elsevier, Amsterdam, 1959, 21 Nyquist, J. K., and Green_hoot, J. H , Responses evoked from the thalamus centrum medianum by painful input: suppression by dorsal funiculus conditioning, Exp, NeuroL; 39 (I973) 215-222. 22 Rieehert, T., Kapp, H., Krainick, L-V., Schmidt, C. L., and Thoden, U;, Operative relief of chronic pain by electrostimulation of 1 23 Shealy, C. N., and Mortimer, J. T,, electrohypalgesia. In F, M. Wageneder
anesthesia, Excerpta AWed. int. Congr. 322-326. 24 Shealy, C. N., Mortimer, J. T., and Hagfors, N. R., Dorsal column electroanalgesia~ J, Neurosurg., 32 (1970) 560-564. 25 Wail, P. D , The sexzsoty and motor role of impulses travelling in the dorsal columns towards cerebral cortex, Brain, 93 (1970) 505-524. 26 Wall, P. D., and Sweet, W. H., Temporary abolition of pain in man, Science, 155 (1967) 108-109. 27 Zotterman, Y., Studies in the peripheral nervous mechanism of pain, Acta reed. seand., 80 (1933) 1-64.
28 Zotterman, Y., The nervous mechanism of touch and pain, Acta psychiat. (Kbh.), 14 (1939) 91-97.
,~ : ~
~
~
"
when theparaes~esias
?i:i~:ii!iCi(ii?L iii!5 ¸ ?i~
:
~:
. . . .
~tanted onthe is pain almost ~ificant as was ~i~e implantation occurred bilaterally also to one side, The eharagesof thresholds generally
i i i i ii i iiii!~i iii~!iiiiiiiiilliiI iii iiiiiii
258 TABLE I
i
i~
RESULTS OF DORSAL COLUMN STIMULATION
Case
Age
C~rus,"of pain
Duration of pain (years)
1
47
2
55
3
40
4
62
5
58
6
52
7 8
43 66
Spinal trauma 3 Paraplegia Spinal trauma 3 Paraplegia Pc~stsurg. 3 Thoracotomy Pc,stsurg. 6 Pyelotomy Pcstsurg. 2 Pyelotomy Brach. plex. trauma 18 Phantom Sciatic 13 Sciatic 12
9
42
Sciatic
27
10
52
Sciatic
10
Previous treatment for pain Myelotomy Symp. block Acopuncture Local vibration Neurotomy Nerve block Nerve block
Sympathectomy Disc surgery Disc surgery Cordotomy~ Disc surger '~ Spinal fusion Disc surgery
Folloiv up Pain relief (moJ~ths) i
3
None*
17
Complete
20
Complete
10
Complete
3
Complete
6
Complete**
23 16
Complete Partial
12
None
14
Partial
* Electrode removed. ** Receiver temporarily removed due to infi.~ction along cable.
DCS has primarily been assumed to inhibit the discharge in small pain fibres segmentally in the dorsal horn by activity descending in the dorsal column fibres 10. It has also been fbund that similar mechanisms for pain inhibition may be: active on a supraspinal levelg,21. In some cases with localized pain, relief may be achieved by electrical[ stimulation of the appropriate peripheral nerve trunk15, zS. During the stimulation the area supplied by the stimulated nerve is oftea found to be analgetic. These effects have been ~nterpreted as being the result of activation of the spinal pain gate. Opposing this view, it has recently been claimed that the analgesia induced by peripheral nerve stimulation is caused by block of AO fibres 5. In these experiments it was. also shown ~that in the analgetic area the threshold for touch was markedly raised. According to a recent report changes irL the sensory perception may also be found during DCS1L Otherwi,se, the patients' ability to perceive cutaneous sensation such as touch, vibration and proprioception has been reported to be hrgely unaffected during such stimutat!on. Not until the intensity of the stimuli was increased to almost intolerable '~evels were there any s~gns of elevation of the sensory thresholds TM. Pain sensation as tested with pin-prick does not seem to be ~dtered by DCS ~9 but when tested with electrical stimulation of the skin the thresheld may be considerably raised ~4. It has also been observed that the sensation of deep pain as provoked by Achilles tendon pinch is sometimes altered and felt as touch onlyz3.
259
Fig, 1. P a t i e m (case 3) with causalgia after left-sided thoracotomy (scar indicated by a crossed line in the lower, left thorax). Antenna for external electrical stimulation attached over receiver in right subclavicular region. Solid line delimits the area with pain and hyperaesthesia, and dotted lines denote the 4 trunk locations where pain thresholds were measured: one close to the scar~ two ad° jacent to the pain area (1) (2), and one contralaterally (3) to the pain area.
The aim of the present study was to investigate, with quantitative methods, the effect o f DCS on the thresholds of touch, vibration and cutaneous pain. The experiments were designed also to look for a correlation between the effect of DCS on spontaneous pain a n d o n t h e various sensory thresholds. The establishment of such a relationship would be of value for the objective evaluation of DCS for treatmem of pain. CL1NrICAL MATERIAL AND METHODS
Material The material consisted of i0 patients undergoing treatment with dorsal column stimulation. As listed, in Table I various conditions of benign, chronic pain were represented. The histories of pain amc anted to a maximum of 27 years, tn 9 patients the dorsal column electrode was implanted at a high thoracic level, slightly dislocated towards the side of the pain, and in one patient (case 6) at a cervical level. With ~he equipment used (Medtronic) the spinal cord is stimulated monopolarly. In 5 cases
• 260
ii ii i:
i) ii!ill ii ~I~!:~I~ ii!ii~i~ili~i~~i ....
(cases 1, 2, 3, 7, 8), the spinal electrode was placed subdurally with the arachn0id left intact, and in the remaining patients layers, was used. The receiver was placed subcutaneously in (see Fig. 1). Prior stimulation applie~ ma~:imal pain. A c, in 8 of the patients patients percutaneous dorsal column stimulation was puncture of the spinal canal with a blunt electrode and during this procedure apartial relief of pain ~as reported. In another patient, DCS was achieved semi-permanent electrode by which a complete alleviation of the pain was achieved, There were no immediate surgical complications but several of the patients experienced a severe, radieular pain located in the thorax at the level of the implant and lasting for about a month postoperatively. In two of the: patients deeubitus appeared about 2 months postoperatively over a short distance of the electrode cable. Presumably, this was caused by tunneling the cable too superficially under the skin, In one of these patients the equipment was remo~ ed since n o positive effect of t h e stimulation had been obtained (case 1). There were no visible changes of the spinal cord h t the electrode plate was c:overed by a thick deposit of fibrous tissue, In the other patient (ease 6), there were a!lso local signs of infection and the receiver and part of the ~:able had to be tempora::ily removed. " h e general results of D,CS were as follows" 6 patients obtained a complete relief cf pain; 2 had a partial relk.f and 2 had no beneficial effect of the stimulation. The o~.3servation time is at present (April 1975) 3-23 months. The 2 patients who are classified as having a partial pain relief initially experienced a good alleviation of pain but the effect decreased 2-4 months postoperatively. These 2 patients are now using transcutaneous stimulation together wi th the DCS and with this combined stimulation they have obtaineda fairly satisfactory relief of pain, For the present st udy, 5 patients were selected who represented different types of pain and were observant and well cooperative in tedious psychophysieal testing (cases 3, 4, 6, 7 and 9 in Tab',~ I). Several months had elapsed after the electrode implantation so that the patients had become fully acquainted with the use of the stimulator and were in a . ,.~ady-state condition, The patients were hospitalJized a n....d subjected to repea~:d testing and close ob.,ervation during at least 3-6 days as regards the prevalence and intensity of pain in relation to the DCS, During the testing sessions the patients were instructed to use the dorsal column stimulators according to a strict time-table which permitted the ~:esting to be performed both when the patients were in a s;tate of maximal spontaneous pain and when being free of pain after an adequate period of DCS. i
6 c ,~
Case .-'~was a 40-yea~,old man with eausalgic pain in the lower part of the left ~hora× (appro~:. Th7-Th10) following a trans-thoracic vagotomy performed 3 years earlier. Because of the pain the seventh iatercostal nerve had been resected but the pain became worse. Anaesthetic block of the tenth intercostal nerve had a beneficial effect and the nerve was therefore~,a s a trhl, exposed and subjected to beta-h'radiafio:n. Following this. the patient experienceda short-lasting, partial pain reAief.
26t ;d but with no effect on the pain. :wo types, one superficial, burning rper- and dysaesthesia for touch, ~termatomes (Fig. 1). Transcutaneous stimulation of the dysaesthetic area resulted in a marked retraction of the Lnd the transevel of 40 Hz tur~ed Case 4 was a 62,year, old woman who since 6 years had suffered from a causalgic pain located in the right waist ,and the groin region following repeated operations for nephrolithiasis. Intercostal nerve~ block ihad be~n tried several times but with a transitory beneficial effect ordy. The patient had a very high comumption of analgetics, both narcotic and non-narcotic. With transcutaneous stimulation applied to the painful area the patient experienced good pain relief but this treatment had to be discontinued due to locaJ irritation of the skin. DCS with 25 Hz and 0.2 msec pulse duration resulted in an almost complete relief of pain and the patient was able to do without narcotic analgetics. Periods of stimulation have decreased )r was used once or twice a day. Upon patient, as well as another in the series nephro- and uretherolithiasis and this,
:affic accident bad a complete evulsion of his right brachial plexus, Since then the arm remained totally denervated and despite of the lack of motility and sensibility the patient has refrained from having his arm amputated. There had been a persisting and severe burning pain which was perceived in the hand and the forearm. In addition, there were attacks of stabbing ache which were almost unbearable. Despite of the pain the patient had been able to maintain his work as a truck driver except for limited periods. Consumption of non-narcotk's was initially very high but has decreased over the years. Two years after: the accident a cervical sympathectomy was performed but with no benefit to ~.hepatient. Transcutaneous stimulation applied to the brachial plexus considerably reduced the pain but there was local irritation of the skin. Therefore, it was decided to perform a dorsal column implant. The spilml electrode was placed at the C4 ~evel and stimulation caused l:,araesthesias to be felt in the right arm only. Stimulation resulted in an almost complete abolition of the pain. Optimal frequency was 100 Hz with a pulse duration
sensory modalities were highly defi:zient in the foot and on the lateral and dorsal aspect of the lower ~eg.
lied on the leg caused a partial relief of pain. Surprisingly, the brachium the effect was equally or even more pronouncegs and there was a total abolition of pain. Optimal stimulus frequency had dropped from an initial value of about 80 V~z to about 30 Hz. The stimulus pulse duration was kept at 0.3 msec. At the time of the study, the patient was free of analgetic drugs and had resumed work for the first tirae since t960., Case 9 was a 42-year-old woman who s~.ffered from low back, sciatic pain since l9 years of age. She had underwent disc surgery 4 times including a fusion owration 5 years before admittance. The chronic back pain had becomeverysevere during the last years and the patient had become more and more disabled. She Was very dependent upon excessively high doses of non-narcotic anatgetics as well as on tranquillizers. There was a slight paresis of the right leg and reduced sertsitivity to vibratory stimulation in the left foot but o~herwise there were no obvious neurologicai deficks. Trans-
262 cutaneous sfimu!atio~ of ~:he dorsal column pain and therefore a felt to invade the pai any effect on the paiJ of time with varyint trials were given up a . . . . . . . . . . . . . pain which confines her to bed most of the day.
Methods The pain threshold was tested by a pair of flat forceps by which a fold of skin was pinched manually with increasing pressure until the subject reported pain. The forceps had a symmetrical rectangular contact area of 10 sq. mm z with blunted margins to avoid incMve violence of the skin. The pressure was recorded by means of a strain gauge the output of which was calibrated in g/sq.mm. The tactile threshold was tested according to Lindblom ~4 by half cycle sinusoidal mechanical pulses applied through a 2 mm diameter blunt probe. The threshold amplitude, expressed in #m, was determined by the method of limits, i.e., the stimulus strength was succe,si'~ly increased with notation of the value when the subject perceived the pulse and then decreased with notation of the value when the sensation disappeared. The mean of the two readings was usually used to denote the threshold. The vibration threshold wa.s determined by applying a 100 Hzsine wave stimulus from an electromagnetic biothesiometer (Bio-Niedical Instr. Inc., Chagrin Falls, Ohio). The stimulator head consisted of a 6 mm diameter plastic probe, with rounded edge. An accelerome~:er was mounted on the shaft of the stimulator, the movement of which was displayed on an oscillo.~cope and calibrated in ~m peak to peak. The stimulator was applied with the l~ressure ef its own weight (440 g) and with the moving shaft in a position which was as near to ~ertical as possible and at the same time perpendicular to ~he skin surface. Care was taken to apply the stimulator to the underlying bone by pllacing tion gave the least var~ati~ . . . . . . . . . . . . . . . . . . . _ ....... .. determined with the method of limits. A full description of the melhod including normal threshold values for commonly used stimulus sites such as the metatarsal and metacarpal regions is in preparation s . RESULTS
The patients had developed a somewhat different routine for the use of the dorsal column stimulator dependent on the type o1' pain and the effect of the stimulation. Thus, for instance, in case 7 the pain was largely tolerable during daytime as long as the patient couldwalk around or move the leg freely. Stimulation was mostly performed during the night when the pain was severe. Switching on the stimulator caused the pain to vanish after 3-6 min. After this period, the voltage was stightly decreased, as guided by the intensity of paraesthesias and b y t h e pafiem's experience of the stimulus intensity required to withhold the pain. If the stimulator was left on the patient could sleep all night and awoke painless. In other cases the ~timutator was
:263
A
B
C
D
E
), in intact and ffore and after r,S1 and Sz, respectively). A befoie, B and D im. The pain threshold (26 g/sq.mm) obtained in location 13 on the trunk (see Fig. 1) was chosen as reference and given the index 100~. Hyphens indicate S.E.M.
F
only used for short periods of? time. In case 3 stimulation for 10 rain was enough abolish the pain for 5 h. The pain-free period had successively increased from 0o~ initially after the operation. During the sessions of sensory testing it was repeatedly confirmed that stimt~ao tion with optimal stimulus parameters caused a reduction of the spontaneous pain
and " ined or stronger stimulation was not tolerated. The was the same in all patients in that they were never felt above the level of the spinal e!ectrode and that the spread in caudal direction primarily occurred ipsilaterally to the side of the pain which was also the side to which the implanted electrode had been slightly shifted° In cases 4 and 7 paraesthesias also appeared in the contralateraI trunk and leg when high stimulus voltages were used tcases3and 9there was no contralateral spread even with the Nghest toleraNe v in the p w i t h the cervical implant (case 6) the paresthesias did not spre~ nd theipsitateral arm and pectoral region. DCSat s s strengths which were subliminal for the provocation of par-
264 pm
/
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111 o
-J o~
200
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m
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0
o
½
1
~½
2
2½
3h
TIME
Fig. 3. Effect of dorsal column stimulation of different intensities (Sz-S4) on the tactile threshold of the right (unaffected) foot sole in case 7. Sz and S2 were sublimina:. 88 optimal and $4 supraoptimal for suppression of pain. Hatching denotes the presence of paxaesthesias. Note low threshold values during Sz, transitory elevation during S2, intermittent elevati, Jn during S8 and consistent elevation during $4. Spontaneous pain, as shown in the bottom of the diagram, was slowly reduced to about 50 70 during $2 and during the initial part of Sa it was rapid!~' and completely abolished.
aesthesias could some'times reduce but never abolish the pain. The thresholds for induced cutaneous pain were generally not significantly influenced by DCS of neither subliminal nor supraliminal intensity. However, there wa,; one exception to this finding. In case 3, some undis threshold when tested within These findings are illustratec the pain area (black columns) was significantly lower than that found in the homologous contralateral area (position 3 in Fig. 1). The thresho! area amounted to 26 g/sq.mm and was arbitrarily given the ir~ ~ngs from this and other trunk positions with normal skin and those from the hands and feet constituted t w o separate sets of data, representing different threshold levels which were all well within normal limits. These da~a were treated as two groups and are represented by hatched and unfilled colum:cs respectively in Fig. 2. The first stimulation (81) was of optimal intensity for the suppression of spontaneous pain and of 3 rain duration. As appears (B), the thresholds of normal skin areas were largely unchanged whe,'eas- that of the hyperpathic pain area h a d risen t o approxi' mately the same normal level as ttae rest of the trunk. Subjectively, the superficial hyperpathic pain had disappeared as well as the hyperaesthesia to touch, ~ i c h now appeared ncrmat on testing with cotton wool. Also the sensation to pinprick and cold and war:nth had lost its unpleasant character. This was lmain~ained
condition
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mn
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Fig. 5. Effect on vibratory threshold of dorsal colum)t stimulation at different intensifies (A, B, C) and frequencies (20-25 Hz, 40-50 Hz, 200 Hz). Filled and empty circles mark 'yes' and'no' responses of tlu'eshold sensation, the difference being the threshold gap. Each point represents the mean of two consecutive measurements made within l rain. Stimulation of metatarsal region. Intensities of DCS: in A producing paraesthesias (pointed area) only in the midthoradc pain area, in B cauda!ily to the foot, in C with the same dis,tribution but stronger. Periods during which DC$ was performed indicated by black bars. Note slight threshold increase during DCS in B, and marked increase during and after DCS in C.
disclose a residual poststimulatory elevation of thresholds for vibration similarly to what was found for touch. In Fig. 5 is illustrated the effi~ct of DCfi of different intens,ifies and frequencies on the vibratory threshold tested in the left metatarsal region in one of the patients. A, B and C rewesent three settings of the DCS voltage, viz. subliminN [A), liminal (B) and suprah~J~mal (C) for paraestheslas m the foot. In .~hls tagure be~N yes an °no' values (see 5{ethods) havi been plotted to illustrate also the effect on the 'thresh, old gap'. It appears that DCS caused an increase of the threshold which was related to the stimulus voltage. There was a]so a considerable increase in the threshold:gap which was most prominent with high stimulus voltage (C). Generally it was not
the D C S o n ~ h e thresholds I~orany type of peripheral stimuli used. DISCUSSION
stimulus implant. replanted the dura esias was , impulse discharge evoked in the dorsal columns and transmitted centripetally via the dorsal column nuclei or centrifugally via segmental dorsN horn collaterals to other ascending tracts such as the spinothalamic1°. It is less likely that the paraesthesias were the results of direct activ~Iion of other pathways than the dorsal column. With the stimulus intensities used in the present study there were no motor responses or sensa-
-
evoked by DCS 18. It is, ne~ssary "go consider the possibility that distraction caused by the spontaneoUslpaJ:nor by the paraesthesiaS during DCS influenced the perception of" ~ e per!pheralsensory stim~ali. This ~s im!ikely for several reasons. The thresholds were ~n no way four~d to be related to the presence er absence of sponta~eou~ palm E~en intensive 'paraestlheSiasin the trunk or legs &d never mgmficantty influence ~ e t L r ~ olds meas~edi ~n'the arms, i.e:, above the level of the spinal etectrede~ The paraes°
268
the~ias disapp -a~ed . . immediately . . . upon. cessation of DCS whereas elevation ~ of: the threshoAs often persisted for some minutes. It can therefore be concluded ~Lhatthe elevation of thresholds was independent of distraction but the result of Stimulation of the dorsal co|utah. In the patients who obtained pain relief :by DCS an elevation 0 f l t h e ~ ¢ s h o ! d S ~ for touch and vibration was consis'tenfly observed belov,(the !e~el:ofthe)spinaI:6le~L~ trode. In contrast, th,,-normal cutaneous thresholds for induced:pain ~ere : , ~n6t ,- itF fluenced. It could be assumed that DCS initiates antidromic impulse discharges ]n fibres mediating touch and vibration and that these discharges collide with thenaturhl orthodromic activity set up by the peripheral stimulation. A collision might occur at any level between tlhe spinal electrode and the peripheral receptor. Anfidromic •impulses may also invade the receptors and reduce their responfivenesslz. An elevation of the sensory thresholds (au~ed by antidromlc discharge :in the primary afferent fibres would be related to the frequency of the DCS. In large cutaneous afferents, the conduction time from the s )inal electrode to the terminals in the foot ma, f be estimated to about 40 msec. The trar smission of the orthodromic impulses from the periphery to the frst segmental relay would require the afferent pathways to be available "~ for a similar period of time. This would imply that dorsal column stimuli applied with intervals of 80 msec, i.e., with a frequency of 12.5 iHz, should cause a partial block unless the DCS and the peripheral stimulation were extremely well timed. At a DC$ frequency of 25 Hz m,. ..... activated dorsal column neurones would be totally blocked for the transmission of impulses 3et up by the peripheral stimulation. The results did not reveal such a frequency-dependent relationship. It is therefore not probable that antidromic blocking is the primary mechanism behind the elevation of sensory thresholds observed during DCS. Besides, the poststimulatory elevation could hardly be explained in terms of such a simple mechanism. Local cl~anges in the cord induced at the ,rite of stimulation12 might interfere with the transmission of touch and vibration and thus to.use a :threshold elevation. A further explanation would be that occlusion occurs in the first synaptilc reiay ~inthe DC nuclei or segmentally in the dorsal horn as a result of impulses descending -,0: antidromically to the segmental collaterals. The explanations given above would imply that the perception of touch and vibration is normally mediated via the dorsal column. This is a much debated question ~,~'5, According to recent experimental data the dorsal column is essential for sensory detection thresholds~L However~ the present results cannot be taken as evidence that this is the case. DCS m~ght interfere with the tested mechanoreceptive functions by way of convergence at a supraspmat le ~/el, whxch may account for m, hibitory effectsL Specific inhibitory systems may al.~o be activated by DC$. Thus, it has been e×perimentally shown that such sfimuhtion may impose an inhibitory effect o n the c~orsat horn units responding to both A - a n d C-fibre input~,9,1oi ~nhibifion may also occur via a supraspina] loop involving the dorsal column nuclei and controlling the inp~at to the spinocervical tract 4. This type of supraspinal iinhibit0ry control has also been shown to be e×erted contralateratly, whichmay be of relevance for the present finding of threshold elevation ~:ontralateral to the DCS
269 Lac~ or effect or v b ~ on m o u c e a cutaneous wa*~tested in an area of dysaesthesia in one
pain. Together with alleviation of pain, D C S caused elevation of thresholds for vibration and touch in all cases except for the one in which stimulation was inefficient for pain relief. Th;s observation may indicate the possibility that the same blocking of pain and in the effects on sensory
ACKNOWLEDGEMENTS
The study was supported by grants from Karolinska Insfitutet and fl'om the Swedish Medical Research Council (B75-14X-4505..01).
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the nor,.is~r
in by ol. ~eia. en
Press, New York, 1974;pp, 749-754: 7 Fox. J2 L. Dorsal column stimulation for relief of intractable pain" problems en.countered with in terms of displacement amplitude. Iggo, A., and Zimmermann. M~; ~gmental and supraspinat acfiens on noxious and non-noxious skin stimuli, Pain, 1 (1975) 14%t65. 10 excitary factors influencing receptive fields of lamina 4spinal cord cells, Exp, BrainRes., 9 (1969) 284-306,
physioL stand,, 44, Supp!, 153 (!958)1.84; !5
........
..............
amplitude
16 Melzack,
and Wall, P. D,, Pain mechanism:
:new
17 Myers, BouraSsal C, and SW t . Brain Res., 70 (1974) :350--355. 18 Nashold, B.' Somjen' i3., ~ and Friedman, H;, tion of the dorsal funiculi in man, Exp, Nekrol.; 36 (1972) 273~287' 19 Nashotd, B. S., Jr., and Friedman, H,, Dorsal column stimulation for control of pain, Preliminary report on 30 Fatients, d. Neuresurg., 36 (1972) 590-597. 20 Noordenbos, W., Pail:, Elsevier, Amsterdam, 1959, 21 Nyquist, J. K., and Green_hoot, J. H , Responses evoked from the thalamus centrum medianum by painful input: suppression by dorsal funiculus conditioning, Exp, NeuroL; 39 (I973) 215-222. 22 Rieehert, T., Kapp, H., Krainick, L-V., Schmidt, C. L., and Thoden, U;, Operative relief of chronic pain by electrostimulation of 1 23 Shealy, C. N., and Mortimer, J. T,, electrohypalgesia. In F, M. Wageneder
anesthesia, Excerpta AWed. int. Congr. 322-326. 24 Shealy, C. N., Mortimer, J. T., and Hagfors, N. R., Dorsal column electroanalgesia~ J, Neurosurg., 32 (1970) 560-564. 25 Wail, P. D , The sexzsoty and motor role of impulses travelling in the dorsal columns towards cerebral cortex, Brain, 93 (1970) 505-524. 26 Wall, P. D., and Sweet, W. H., Temporary abolition of pain in man, Science, 155 (1967) 108-109. 27 Zotterman, Y., Studies in the peripheral nervous mechanism of pain, Acta reed. seand., 80 (1933) 1-64.
28 Zotterman, Y., The nervous mechanism of touch and pain, Acta psychiat. (Kbh.), 14 (1939) 91-97.
