Acta nenrol. scandinav. 54, 192-199, 1976
Department of Clinical Neurophysiology, University Central Hospital, Turku, and the Department of Neurology, University of Turku, Finland.
DIAGNOSTIC POSSIBILITIES FOR THE NUCHAL EVOKED POTENTIAL
M. J. KOIVIKKO, A. H. LANGand B. FALCK ABSTRACT As a response to stimulation of the arm nerves an evoked potential can be recorded i n the posterior neck region i n man. This nuchal evoked potential (NEP) was recorded in three selected patients with A ) cervical rib, B) syringomyelia, and C) prolapse of cervical intervertebral disc. Patients A and C had low-amplitudic NEPs with increased latencies when the affected side was stimulated and “normal” NEPs when the unaffected side was stimulated. Patient B had grossly abnormal, polyphasic NEPs (regardless of the side stimulated) but the simultaneously recorded somatosensory evoked potential was “normal”. No systematic differences in the parameters of the NEP due to different recording locations on the neck could be observed.
The possibilities of making direct, but non-invasive measurements of the function of the spinal cord and its roots in man are at present limited. However, by using the averaging method (Dawson 1947), it is possible with surface electrodes to record on the posterior neck region a potential as a response to stimulation of the arm nerves (Cracco 1973, Liberson & Kim 1963). This potential, also called the nuchal evoked potential (NEP) (Koiuikko 1975 a ) , probably originates in the spinal cord. It consists of three phases ( positive-negative-positive) , the negative phase being a rather conspicuous peak. In adults the latency of the NEP depends on the length of the arm (Koiuikko 1975 b, Matthews e f al. 1974). A corresponding potential can be recorded over the lumbar, thoracic and cervical spine as a response to the stimulation of the leg nerves (Cracco & Cracco 1975, Cracco 1973). In the literature on the subject, up to now there have been only a few observations concerning the clinical use of the NEP (Cracco & Cracco 1975, Cracco 1973, Mortillaro & Emser 1974). The parameters of the NEP (Koiuikko 1975 a ) have not been tested in clinical practice and it is thus im-
possible to know whether the NEPs recorded in patients deviate significantly from the normal. However, as will be shown in the present study, the examination of three selected patients demonstrate the definite diagnostic value of recording the IVEP. METHODS Square wave electrical pulses werc used as stimuli. They were delivered through bipolar surface electrodes (DISA 13 K 62) b y a constant voltage stimulator (DISA 13 G 04) to the arm nerves a t the wrist o r sometimes a t the elbow. The stimulation frequency was usually 3 c/sec and the pulse duration 0.1 msec. The intensity of the stimuli was so adjusted that a slight muscle twitch of t h e corresponding muscle was ohserved. The electrical activity of t h e posterior neck region was recorded monopolarly with three ehlorided silver disc electrodes. They were placed i n t h e mid-line a t the levels indicated i n Figure 1 ; hereinafter these 1 as I, 11 and 111. The electrodes were fixed to t h e skin with adhesive tape. Two silver pad electrodes were placed a t C4 and C3 (International 10-20 System) to record the somatosensory evoked potential ( S E P ) . A l l these electrodes were referred to a silver-disc electrode a t the bridge of the nose. The electrical activity was amplified w i t h a Nikon Kohden EEG-apparatus, bandpass 0.5-60 c/sec ( a t - 3 dB down) and was then fed into a DIDAC 4000 (Intcrtechnique) multichannel analogue/digital analyser. Using the triggering pre-pulse from the stimulator, either 250, 500 or 2,000 potentials, event-related to the stimulus, were summated. LJsing t h e address selector of t h e analyser, each address could be separately identified and t h e latencies were t h u s determined digitally, usually with an accuracy of 200 p s ( = address time). The signals could also be photographed from the calibrated screen of the analyser.
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Department of Clinical Neurophysiology, University Central Hospital, Turku, and the Department of Neurology, University of Turku, Finland.
DIAGNOSTIC POSSIBILITIES FOR THE NUCHAL EVOKED POTENTIAL
M. J. KOIVIKKO, A. H. LANGand B. FALCK ABSTRACT As a response to stimulation of the arm nerves an evoked potential can be recorded i n the posterior neck region i n man. This nuchal evoked potential (NEP) was recorded in three selected patients with A ) cervical rib, B) syringomyelia, and C) prolapse of cervical intervertebral disc. Patients A and C had low-amplitudic NEPs with increased latencies when the affected side was stimulated and “normal” NEPs when the unaffected side was stimulated. Patient B had grossly abnormal, polyphasic NEPs (regardless of the side stimulated) but the simultaneously recorded somatosensory evoked potential was “normal”. No systematic differences in the parameters of the NEP due to different recording locations on the neck could be observed.
The possibilities of making direct, but non-invasive measurements of the function of the spinal cord and its roots in man are at present limited. However, by using the averaging method (Dawson 1947), it is possible with surface electrodes to record on the posterior neck region a potential as a response to stimulation of the arm nerves (Cracco 1973, Liberson & Kim 1963). This potential, also called the nuchal evoked potential (NEP) (Koiuikko 1975 a ) , probably originates in the spinal cord. It consists of three phases ( positive-negative-positive) , the negative phase being a rather conspicuous peak. In adults the latency of the NEP depends on the length of the arm (Koiuikko 1975 b, Matthews e f al. 1974). A corresponding potential can be recorded over the lumbar, thoracic and cervical spine as a response to the stimulation of the leg nerves (Cracco & Cracco 1975, Cracco 1973). In the literature on the subject, up to now there have been only a few observations concerning the clinical use of the NEP (Cracco & Cracco 1975, Cracco 1973, Mortillaro & Emser 1974). The parameters of the NEP (Koiuikko 1975 a ) have not been tested in clinical practice and it is thus im-
possible to know whether the NEPs recorded in patients deviate significantly from the normal. However, as will be shown in the present study, the examination of three selected patients demonstrate the definite diagnostic value of recording the IVEP. METHODS Square wave electrical pulses werc used as stimuli. They were delivered through bipolar surface electrodes (DISA 13 K 62) b y a constant voltage stimulator (DISA 13 G 04) to the arm nerves a t the wrist o r sometimes a t the elbow. The stimulation frequency was usually 3 c/sec and the pulse duration 0.1 msec. The intensity of the stimuli was so adjusted that a slight muscle twitch of t h e corresponding muscle was ohserved. The electrical activity of t h e posterior neck region was recorded monopolarly with three ehlorided silver disc electrodes. They were placed i n t h e mid-line a t the levels indicated i n Figure 1 ; hereinafter these 1 as I, 11 and 111. The electrodes were fixed to t h e skin with adhesive tape. Two silver pad electrodes were placed a t C4 and C3 (International 10-20 System) to record the somatosensory evoked potential ( S E P ) . A l l these electrodes were referred to a silver-disc electrode a t the bridge of the nose. The electrical activity was amplified w i t h a Nikon Kohden EEG-apparatus, bandpass 0.5-60 c/sec ( a t - 3 dB down) and was then fed into a DIDAC 4000 (Intcrtechnique) multichannel analogue/digital analyser. Using the triggering pre-pulse from the stimulator, either 250, 500 or 2,000 potentials, event-related to the stimulus, were summated. LJsing t h e address selector of t h e analyser, each address could be separately identified and t h e latencies were t h u s determined digitally, usually with an accuracy of 200 p s ( = address time). The signals could also be photographed from the calibrated screen of the analyser.
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