AN ELECTRODIAGNOSTIC TECHNIQUE FOR ASSESSING PALMAR PROPER DIGITAL NERVES OF THE HAND: NORMATIVE DATA AND CLINICAL APPLICATION GIAMPIETRO ZANETTE, MD,1 MATTEO FRANCESCO LAURIOLA, BSc,1 and STEFANO TAMBURIN, MD, PhD2 1 2
Neurology Unit, Pederzoli Hospital, Peschiera del Garda, Italy Department of Neurological and Movement Sciences, University of Verona, Piazzale Scuro 10, I-37134, Verona, Italy
Accepted 24 March 2015 ABSTRACT: Introduction: There is no standard electrodiagnostic technique for palmar proper digital nerves (PaPDNs). In this study we investigated sensory nerve action potentials (SNAPs) to PaPDN stimulation in normal subjects and patients. Methods: SNAPs of PaPDNs were recorded in response to selective antidromic stimulation at the web space and mixed nerve stimulation at the wrist in 14 controls. The selectivity of PaPDN stimulation and the effect of recording electrode position on SNAP amplitude were studied. The technique was tested in 2 patients with PaPDN lesions. Results: The technique yielded selective PaPDN stimulation at the web space. SNAP amplitude to PaPDN stimulation was influenced by age and was larger than SNAP amplitude to wrist stimulation. The recording electrode positions influenced SNAP amplitude. In patients, we documented PaPDN lesions, which were confirmed at surgery, whereas conventional wrist mixed nerve stimulation yielded negative findings. Conclusions: Selective PaPDN stimulation at the web space is feasible and may be helpful for electrodiagnosis of PaPDN lesions. Muscle Nerve 52: 972–980, 2015
The palmar proper digital nerves (PaPDNs) are the sensory terminal branches of the ulnar and median nerves.1 Two PaPDNs course along the sides of each finger (i.e., on the ulnar/medial and the radial/lateral aspects), and they supply the palmar aspect of all fingers and the distal dorsal aspect of the first 3 fingers.2 The median PaPDNs branch from the 3 palmar divisions of the median nerve (PDMN) and innervate the thumb, index, and middle fingers, and the lateral aspect of the ring finger (Fig. 1). The ulnar PaPDNs derive from the superficial ulnar branch (SUB) and innervate the medial aspect of the ring fingers and the small finger (Fig. 1). The dorsal proper digital nerves derive from the radial nerve and the dorsal branch of the ulnar nerve, but their contribution to the sensory innervation of the fingers is minor.3
Additional Supporting Information may be found in the online version of this article. Abbreviations: ANOVA, analysis of variance; CPDN, common palmar digital nerve; CTS, carpal tunnel syndrome; PaPDN, palmar proper digital nerve; PDMN, palmar division of the median nerve; SNAP, sensory nerve action potential; SNCV, sensory nerve conduction velocity; SUB, superficial ulnar branch Key words: electrodiagnosis; median nerve; proper digital nerve; selective stimulation; ulnar nerve Correspondence to: S. Tamburin; e-mail: [email protected] C 2015 Wiley Periodicals, Inc. V
Published online 3 April 2015 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/mus.24668
972
NCS of Palmar Proper Digital Nerves
Trauma of the palm of the hand and fingers is common and may involve the PDMNs, the SUB and its divisions, or the PaPDNs.4 Recent progress in microsurgical techniques for repairing and grafting peripheral nerves produces a consistently better outcome.5 Thus, identification of PaPDN lesions after hand trauma is important to select patients who will undergo surgery, but there is no accepted electrodiagnostic technique for evaluating these nerves. Except for the fourth finger, orthodromic (stimulation of the finger, recording at the wrist) and antidromic (stimulation at the wrist, recording from the finger) nerve conduction studies with either ring or needle electrodes cannot consistently separate the sensory nerve action potentials (SNAPs) of the 2 PaPDNs innervating each finger because of innervation overlap, volume conduction artifacts, and spread of the stimulating current to the intact PaPDN.1,3 As a result, standard electrodiagnostic techniques often yield false negative or inconclusive findings after damage to PDMNs or a single PaPDN. Modified electrodes and/or techniques may offer a better separation of the 2 SNAPs from the same finger, but no clear-cut confirmation of a PaPDN lesion.1,3,6 Some studies suggest the use of anesthetic nerve block,1,6,7 but this procedure is time-consuming and invasive. A report offered proof-of-concept evidence that selective antidromic stimulation of the PDMNs may yield a higher diagnostic certainty, but only 2 patients with middle finger PaPDN lesions were studied.3 This study was designed to investigate the SNAPs obtained from selective antidromic stimulation of the PaPDNs. Toward this aim, we studied a group of normal subjects to derive normative data. We compared the data with those obtained from standard nerve conduction studies and investigated the selectivity of the stimulation technique and the effect of different recording electrode positions. The technique was also validated in 2 patients with PaPDN damage. METHODS
We included 14 normal controls (7 men, ages 45.5 6 14.1 years, range 28–70 years). Subjects gave written informed consent before inclusion in the study, which was performed according to the MUSCLE & NERVE
December 2015
2A). The reference electrode (anode) was placed on the dorsum of the hand in the space between 2 adjacent metacarpophalangeal joints (Fig. 2B). The SNAPs were recorded (sensitivity 20 lV/division; bandpass filter 10–2,000 HZ) from a pair of 15 3 12 mm Ag–AgCl surface electrodes placed on the medial and lateral aspects of the fingers at the proximal and distal interphalangeal joints set 3 cm apart from each other (Fig. 2A and B). Figure 2C shows the position where the stimulating cathode was placed according to the anatomy of median and ulnar nerve sensory branches. Figure 2D shows the stimulating cathode position in relation to the hand surface anatomy and the palmar creases. The stimulus intensity was initially set at 0.5 mA and then increased in 0.5-mA steps until a supramaximal SNAP was recorded.
FIGURE 1. The anatomy of the 3 palmar divisions of the median nerve (PDMNs), the superficial ulnar branch (SUB), and the palmar proper digital nerves (PaPDNs) in the left hand of a normal subject as derived from ultrasound nerve imaging. The first/lateral PDMN bifurcates into 1 branch further dividing into the thumb PaPDNs and another branch that becomes the index finger lateral PaPDN. The second/intermediate and third/medial PDMNs divide into the corresponding PaPDNs in the digit web space at the level of the metacarpophalangeal joint. The SUB divides into the small finger medial PaPDN and a common palmar digital nerve (CPDN) that further bifurcates into 2 PaPDNs. Continuous lines indicate median nerve sensory branches, whereas dashed lines show ulnar nerve sensory branches. Note that motor branches are not shown in the figure.
Declaration of Helsinki and was approved by the local ethics committee. All subjects underwent selective antidromic stimulation of the PaPDNs according to a standard electrodiagnostic technique (i.e., mixed nerve stimulation at the wrist). The selectivity of PaPDN stimulation and the effect of recording electrodes were examined in a subgroup of 6 subjects (3 men, ages 40.8 6 13.1 years, range 28–59 years). PaPDN Stimulation. SNAPs were recorded with Sierra Wave (Cadwell, Kennewick, Washington) electromyograph for response to antidromic stimulation (stimulus duration 0.1 ms) of the PaPDNs. The stimulating cathode was a needle electrode placed in the web space between the bases of 2 adjacent fingers in the distal part of the palm at the level of the metacarpophalangeal joint (Fig. NCS of Palmar Proper Digital Nerves
Mixed Nerve Stimulation at the Wrist. To compare the selective antidromic PaPDN electrodiagnostic technique to a standard one, SNAPs from single PaPDNs of each finger were recorded with antidromic stimulation (stimulus duration 0.1 ms, stimulus intensity set at 1 mA, then increased by 1 mA until a supramaximal SNAP was recorded) of the ulnar and median nerves at the wrist with a bipolar stimulator. The recording electrode type and position, sensitivity, and bandpass filters were the same as for selective PaPDN stimulation. Selectivity of PaPDN Stimulation. To investigate the selectivity of PaPDN stimulation with this technique, the second and third web spaces were studied. In Condition A, the second web space was stimulated (Fig. 3A, open circle), and we recorded SNAPs from the medial index finger PaPDN (test response, open rectangles in Fig. 3A) and the lateral ring finger PaPDN (control response, filled rectangles). In Condition B, the third web space was stimulated (Fig. 3A, filled circle), and SNAPs were recorded from the lateral ring finger PaPDN (test response, closed rectangles) and the medial index finger PaPDN (control response, open rectangles). In both conditions, stimulation was increased to twice the intensity that could achieve maximal SNAP amplitude in the test response. In cases of selective PaPDN stimulation, a SNAP was to be expected in the test response but not in the control response. However, the presence of a SNAP in the control response would indicate either non-selective PaPDN stimulation (i.e., stimulation of PaPDNs from 2 contiguous PDMNs) or the presence of a volume-conducted response. In Condition A, after the needle was inserted in the second web space according to the surface anatomy and the palmar creases (Fig. 3A) and a supramaximal SNAP was obtained from the medial index finger PaPDN with evidence of no SNAP from the MUSCLE & NERVE
December 2015
973
FIGURE 2. The montages for recording sensory nerve action potentials (SNAPs) by antidromic stimulation of the palmar proper digital nerves (PaPDNs). (A, B) Montage for studying the index finger medial PaPDN SNAP. The stimulating needle cathode was placed on the palmar side of the hand in the web space between the bases of 2 fingers in the distal part of the palm at the level of the metacarpophalangeal joint (A), and the reference anode was placed on the dorsal surface of the hand in the space between 2 adjacent metacarpophalangeal joints corresponding to the cathode (B). The recording electrodes were placed on the medial/lateral aspect of the finger at the proximal and distal interphalangeal joints set 3 cm apart from each other (A, B). (C) Position of the stimulating cathode (䊊) according to the anatomy of the PaPDNs. When the stimulating electrode was placed in the second, third, and fourth web spaces, 2 PaPDNs innervating 2 different fingers were stimulated. (D) Position of the stimulating cathode (䊊) in relation to the hand surface anatomy and the distal and proximal palmar creases. The fingers were slightly flexed to better show the palmar creases.
lateral ring finger PaPDN (Fig. 3B), we checked the position of the stimulated nerve (i.e., the second PDMN and/or the PaPDNs branching from it), that of the nerve not intended to be stimulated (i.e., the third PDMN and/or the corresponding PaPDNs), and that of the needle cathode on an ultrasound machine (Xario 200; Toshiba Medical Systems Europe, Zoetermeer, Holland) equipped with a high-frequency bandwidth (13–18 MHZ) PLU1204BT linear-array transducer (refer to video in Supplementary Material, available online). 974
NCS of Palmar Proper Digital Nerves
Effect of Recording Electrode Position. We examined the effect of the position of surface electrode on the amplitude of the PaPDN SNAPs. The second web space was stimulated, and the amplitude of the medial index finger PaPDN SNAPs was recorded from 2 pairs of 15 3 12-mm Ag–AgCl surface electrodes placed on the medial (test response) and lateral (control response) sides of the index finger.
All tests were performed using (version 20.0) statistical software.
Statistical Analysis.
IBM
SPSS
MUSCLE & NERVE
December 2015
FIGURE 3. (A) The setting for studying the selectivity of palmar proper digital nerve (PaPDN) stimulation. The second web space was stimulated in Condition A (䊊), and SNAPs were recorded from the medial index finger PaPDN (test response, ‘) and the lateral ring finger PaPDN (control response, ). In Condition B, the third web space was stimulated (•), and SNAPs were recorded from the lateral ring finger PaPDN (test response, ) and the medial index finger PaPDN (control response, ‘). (B) SNAPs recorded from the medial index finger and lateral ring finger PaPDNs in Conditions A and B in the left hand of a normal subject.
Continuous variables were reported as mean 6 SD, except when otherwise stated. The normality of SNAP distribution was examined with the skewness kurtosis test. SNAP skewed distributions were logarithmically transformed before calculating mean and SD, and data were transformed back to original units by antilog transformation.8 The effect of gender, age group (>45 or
Neurology Unit, Pederzoli Hospital, Peschiera del Garda, Italy Department of Neurological and Movement Sciences, University of Verona, Piazzale Scuro 10, I-37134, Verona, Italy
Accepted 24 March 2015 ABSTRACT: Introduction: There is no standard electrodiagnostic technique for palmar proper digital nerves (PaPDNs). In this study we investigated sensory nerve action potentials (SNAPs) to PaPDN stimulation in normal subjects and patients. Methods: SNAPs of PaPDNs were recorded in response to selective antidromic stimulation at the web space and mixed nerve stimulation at the wrist in 14 controls. The selectivity of PaPDN stimulation and the effect of recording electrode position on SNAP amplitude were studied. The technique was tested in 2 patients with PaPDN lesions. Results: The technique yielded selective PaPDN stimulation at the web space. SNAP amplitude to PaPDN stimulation was influenced by age and was larger than SNAP amplitude to wrist stimulation. The recording electrode positions influenced SNAP amplitude. In patients, we documented PaPDN lesions, which were confirmed at surgery, whereas conventional wrist mixed nerve stimulation yielded negative findings. Conclusions: Selective PaPDN stimulation at the web space is feasible and may be helpful for electrodiagnosis of PaPDN lesions. Muscle Nerve 52: 972–980, 2015
The palmar proper digital nerves (PaPDNs) are the sensory terminal branches of the ulnar and median nerves.1 Two PaPDNs course along the sides of each finger (i.e., on the ulnar/medial and the radial/lateral aspects), and they supply the palmar aspect of all fingers and the distal dorsal aspect of the first 3 fingers.2 The median PaPDNs branch from the 3 palmar divisions of the median nerve (PDMN) and innervate the thumb, index, and middle fingers, and the lateral aspect of the ring finger (Fig. 1). The ulnar PaPDNs derive from the superficial ulnar branch (SUB) and innervate the medial aspect of the ring fingers and the small finger (Fig. 1). The dorsal proper digital nerves derive from the radial nerve and the dorsal branch of the ulnar nerve, but their contribution to the sensory innervation of the fingers is minor.3
Additional Supporting Information may be found in the online version of this article. Abbreviations: ANOVA, analysis of variance; CPDN, common palmar digital nerve; CTS, carpal tunnel syndrome; PaPDN, palmar proper digital nerve; PDMN, palmar division of the median nerve; SNAP, sensory nerve action potential; SNCV, sensory nerve conduction velocity; SUB, superficial ulnar branch Key words: electrodiagnosis; median nerve; proper digital nerve; selective stimulation; ulnar nerve Correspondence to: S. Tamburin; e-mail: [email protected] C 2015 Wiley Periodicals, Inc. V
Published online 3 April 2015 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/mus.24668
972
NCS of Palmar Proper Digital Nerves
Trauma of the palm of the hand and fingers is common and may involve the PDMNs, the SUB and its divisions, or the PaPDNs.4 Recent progress in microsurgical techniques for repairing and grafting peripheral nerves produces a consistently better outcome.5 Thus, identification of PaPDN lesions after hand trauma is important to select patients who will undergo surgery, but there is no accepted electrodiagnostic technique for evaluating these nerves. Except for the fourth finger, orthodromic (stimulation of the finger, recording at the wrist) and antidromic (stimulation at the wrist, recording from the finger) nerve conduction studies with either ring or needle electrodes cannot consistently separate the sensory nerve action potentials (SNAPs) of the 2 PaPDNs innervating each finger because of innervation overlap, volume conduction artifacts, and spread of the stimulating current to the intact PaPDN.1,3 As a result, standard electrodiagnostic techniques often yield false negative or inconclusive findings after damage to PDMNs or a single PaPDN. Modified electrodes and/or techniques may offer a better separation of the 2 SNAPs from the same finger, but no clear-cut confirmation of a PaPDN lesion.1,3,6 Some studies suggest the use of anesthetic nerve block,1,6,7 but this procedure is time-consuming and invasive. A report offered proof-of-concept evidence that selective antidromic stimulation of the PDMNs may yield a higher diagnostic certainty, but only 2 patients with middle finger PaPDN lesions were studied.3 This study was designed to investigate the SNAPs obtained from selective antidromic stimulation of the PaPDNs. Toward this aim, we studied a group of normal subjects to derive normative data. We compared the data with those obtained from standard nerve conduction studies and investigated the selectivity of the stimulation technique and the effect of different recording electrode positions. The technique was also validated in 2 patients with PaPDN damage. METHODS
We included 14 normal controls (7 men, ages 45.5 6 14.1 years, range 28–70 years). Subjects gave written informed consent before inclusion in the study, which was performed according to the MUSCLE & NERVE
December 2015
2A). The reference electrode (anode) was placed on the dorsum of the hand in the space between 2 adjacent metacarpophalangeal joints (Fig. 2B). The SNAPs were recorded (sensitivity 20 lV/division; bandpass filter 10–2,000 HZ) from a pair of 15 3 12 mm Ag–AgCl surface electrodes placed on the medial and lateral aspects of the fingers at the proximal and distal interphalangeal joints set 3 cm apart from each other (Fig. 2A and B). Figure 2C shows the position where the stimulating cathode was placed according to the anatomy of median and ulnar nerve sensory branches. Figure 2D shows the stimulating cathode position in relation to the hand surface anatomy and the palmar creases. The stimulus intensity was initially set at 0.5 mA and then increased in 0.5-mA steps until a supramaximal SNAP was recorded.
FIGURE 1. The anatomy of the 3 palmar divisions of the median nerve (PDMNs), the superficial ulnar branch (SUB), and the palmar proper digital nerves (PaPDNs) in the left hand of a normal subject as derived from ultrasound nerve imaging. The first/lateral PDMN bifurcates into 1 branch further dividing into the thumb PaPDNs and another branch that becomes the index finger lateral PaPDN. The second/intermediate and third/medial PDMNs divide into the corresponding PaPDNs in the digit web space at the level of the metacarpophalangeal joint. The SUB divides into the small finger medial PaPDN and a common palmar digital nerve (CPDN) that further bifurcates into 2 PaPDNs. Continuous lines indicate median nerve sensory branches, whereas dashed lines show ulnar nerve sensory branches. Note that motor branches are not shown in the figure.
Declaration of Helsinki and was approved by the local ethics committee. All subjects underwent selective antidromic stimulation of the PaPDNs according to a standard electrodiagnostic technique (i.e., mixed nerve stimulation at the wrist). The selectivity of PaPDN stimulation and the effect of recording electrodes were examined in a subgroup of 6 subjects (3 men, ages 40.8 6 13.1 years, range 28–59 years). PaPDN Stimulation. SNAPs were recorded with Sierra Wave (Cadwell, Kennewick, Washington) electromyograph for response to antidromic stimulation (stimulus duration 0.1 ms) of the PaPDNs. The stimulating cathode was a needle electrode placed in the web space between the bases of 2 adjacent fingers in the distal part of the palm at the level of the metacarpophalangeal joint (Fig. NCS of Palmar Proper Digital Nerves
Mixed Nerve Stimulation at the Wrist. To compare the selective antidromic PaPDN electrodiagnostic technique to a standard one, SNAPs from single PaPDNs of each finger were recorded with antidromic stimulation (stimulus duration 0.1 ms, stimulus intensity set at 1 mA, then increased by 1 mA until a supramaximal SNAP was recorded) of the ulnar and median nerves at the wrist with a bipolar stimulator. The recording electrode type and position, sensitivity, and bandpass filters were the same as for selective PaPDN stimulation. Selectivity of PaPDN Stimulation. To investigate the selectivity of PaPDN stimulation with this technique, the second and third web spaces were studied. In Condition A, the second web space was stimulated (Fig. 3A, open circle), and we recorded SNAPs from the medial index finger PaPDN (test response, open rectangles in Fig. 3A) and the lateral ring finger PaPDN (control response, filled rectangles). In Condition B, the third web space was stimulated (Fig. 3A, filled circle), and SNAPs were recorded from the lateral ring finger PaPDN (test response, closed rectangles) and the medial index finger PaPDN (control response, open rectangles). In both conditions, stimulation was increased to twice the intensity that could achieve maximal SNAP amplitude in the test response. In cases of selective PaPDN stimulation, a SNAP was to be expected in the test response but not in the control response. However, the presence of a SNAP in the control response would indicate either non-selective PaPDN stimulation (i.e., stimulation of PaPDNs from 2 contiguous PDMNs) or the presence of a volume-conducted response. In Condition A, after the needle was inserted in the second web space according to the surface anatomy and the palmar creases (Fig. 3A) and a supramaximal SNAP was obtained from the medial index finger PaPDN with evidence of no SNAP from the MUSCLE & NERVE
December 2015
973
FIGURE 2. The montages for recording sensory nerve action potentials (SNAPs) by antidromic stimulation of the palmar proper digital nerves (PaPDNs). (A, B) Montage for studying the index finger medial PaPDN SNAP. The stimulating needle cathode was placed on the palmar side of the hand in the web space between the bases of 2 fingers in the distal part of the palm at the level of the metacarpophalangeal joint (A), and the reference anode was placed on the dorsal surface of the hand in the space between 2 adjacent metacarpophalangeal joints corresponding to the cathode (B). The recording electrodes were placed on the medial/lateral aspect of the finger at the proximal and distal interphalangeal joints set 3 cm apart from each other (A, B). (C) Position of the stimulating cathode (䊊) according to the anatomy of the PaPDNs. When the stimulating electrode was placed in the second, third, and fourth web spaces, 2 PaPDNs innervating 2 different fingers were stimulated. (D) Position of the stimulating cathode (䊊) in relation to the hand surface anatomy and the distal and proximal palmar creases. The fingers were slightly flexed to better show the palmar creases.
lateral ring finger PaPDN (Fig. 3B), we checked the position of the stimulated nerve (i.e., the second PDMN and/or the PaPDNs branching from it), that of the nerve not intended to be stimulated (i.e., the third PDMN and/or the corresponding PaPDNs), and that of the needle cathode on an ultrasound machine (Xario 200; Toshiba Medical Systems Europe, Zoetermeer, Holland) equipped with a high-frequency bandwidth (13–18 MHZ) PLU1204BT linear-array transducer (refer to video in Supplementary Material, available online). 974
NCS of Palmar Proper Digital Nerves
Effect of Recording Electrode Position. We examined the effect of the position of surface electrode on the amplitude of the PaPDN SNAPs. The second web space was stimulated, and the amplitude of the medial index finger PaPDN SNAPs was recorded from 2 pairs of 15 3 12-mm Ag–AgCl surface electrodes placed on the medial (test response) and lateral (control response) sides of the index finger.
All tests were performed using (version 20.0) statistical software.
Statistical Analysis.
IBM
SPSS
MUSCLE & NERVE
December 2015
FIGURE 3. (A) The setting for studying the selectivity of palmar proper digital nerve (PaPDN) stimulation. The second web space was stimulated in Condition A (䊊), and SNAPs were recorded from the medial index finger PaPDN (test response, ‘) and the lateral ring finger PaPDN (control response, ). In Condition B, the third web space was stimulated (•), and SNAPs were recorded from the lateral ring finger PaPDN (test response, ) and the medial index finger PaPDN (control response, ‘). (B) SNAPs recorded from the medial index finger and lateral ring finger PaPDNs in Conditions A and B in the left hand of a normal subject.
Continuous variables were reported as mean 6 SD, except when otherwise stated. The normality of SNAP distribution was examined with the skewness kurtosis test. SNAP skewed distributions were logarithmically transformed before calculating mean and SD, and data were transformed back to original units by antilog transformation.8 The effect of gender, age group (>45 or
