Each digital branch of the median nerve was stimulated in turn in 34 women (55 hands) with carpal tunnel syndrome (CTS). The amplitude and conduction velocity of the sensory nerve action potential (SNAP) recorded at the wrist, and the threshold for patient perception of the electrical stimuIus on the median innervated sides of each digit, were compared with the corresponding values in a group of asymptomatic, age-matched women. Sensory conduction velocity or SNAP amplitude were abnormal in more than 80% of all digital nerves studied apart from those in the index finger. Stimulation of digital nerves in the index finger proved the least sensitive means of detecting the electrophysiologicalabnormality. We conclude that selective digital nerve stimulation is a sensitive technique in the diagnosis of CTS. If ring electrodes are preferred, our results suggest that the middle rather than the index finger should be used. Key words: carpal tunnel syndrome digital nerve stimulation MUSCLE & NERVE 13:601-606 1990
CARPAL TUNNEL SYNDROME: WHICH FINGER SHOULD BE TESTED? AN ANALYSIS OF SENSORY CONDUCTION IN DIGITAL BRANCHES OF THE MEDIAN NERVE RICHARD A.L. MACDONELL, MBBS, FRACP, MARTIN S. SCHWARTZ, MD, and MICHAEL SWASH, MD, FRCP
Compression of the median nerve in the carpal tunnel causing carpal tunnel syndrome (CTS), is usually an idiopathic disorder, occurring especially in women.576Symptoms include arm pain, often worse at night, and paresthesias in median innervated digits. The nerve supply to these digits comes from the division of the median nerve into four sensory branches and a motor branch to thenar muscles shortly after it exits from the distal end of the carpal tunnel. The most lateral sensory branch becomes th2 digital nerve in the lateral side of the thumb. T h e remaining three subdivide into digital branches supplying adjacent sides of the thumb, index, middle and ring fingers.' CTS may be confirmed electrophysiologically. Characteristic findings are slowing of sensory conduction velocity
From the Department of Neurology, The London Hospital, Whitechapel E l 155. London, United Kingdom (Dr Macdonell. Dr. Swash), and the Department of Neurology, Atkinson Morley's Hospital, Wirnbledon, London, United Kingdom (Dr Schwartz)
and reduction in the amplitude of the sensory nerve action potential (SNAP) between digit and wrist in the median nerve.3*4,10,14*22 These abnormalities may be restricted to only one or two of the nerve's digital branches."." A common method of investigation is to use ring electrodes to stimulate or record from one digit while recording or stimulating, as appropriate, at the wrist. The sensitivity of such testing for CTS may be increased by usin an "inching" technique," by forced wrist or by producing ischemia' of the affected hand. Typically the index or middle fingers have been used, but recent studies suggest that using the thumb or ring finger may improve the sensitivity of electrophysiological d i a g n ~ s i s . " ~ ~ ' ~ ' ~ ~ The aim of this study was to determine the relative frequency of abnormal sensory conduction from the seven digital branches of the median nerve in a group of 34 women with idiopathic CTS.
Dr Macdonell is supported by a Commonwealth Medical Fellowship
MATERIALS AND METHODS
Address reprint requests to Dr. Swash, FRCP, at the Department of Neurology, The London Hospital, Whitechapel, London E l 165, United Kingdom.
Thirty-four consecutive women referred because of clinical symptoms consistent with CTS were studied. In each, the diagnosis was confirmed by routine electrophysiological testing. These women were compared with an age-matched control pop-
Accepted for publication August 7. 1989 CCC 0148-639x/90/070601-06$04.00 0 1990 John Wiley & Sons, Inc.
Digital Nerve Stimulation in CTS
MUSCLE & NERVE
July 1990
601
ulation of 12 women without clinical features of CTS. All patients and control subjects gave informed consent. CTS was bilateral in 22 patients and unilateral in 12. Each patient complained of hand or arm pain, often worse at night, and paresthesias affecting one or more digits. A generalized neuropathy was excluded, in each case, by normal ulnar nerve motor and sensory conduction velocities and normal radial nerve sensory studies in both arms. The electrophysiological criteria used to diagnose CTS were at least two of the following: (1) a distal motor latency from the wrist to thenar eminence > 4.2 msec, (2) SNAP amplitude < 10 pV, (3) SNAP conduction velocity < 40 m/ sec, (4)SNAP amplitude less than that of the ipsilateral ulnar nerve at the wrist, or (5) median motor or sensory latencies at the wrist more than 0.5 msec longer than its counterpart on the opposite hand (gain 500 pV/div). These values are routinely used in our laboratory for the diagnosis of CTS. The latency of the SNAP was measured from the onset of the response. Needle electromyographic studies of the abductor pollicis brevis muscle were not performed. All hands, patients and controls, were warmed prior to testing by seating the patient for 15 minutes in a room at 22"-24"C in which the studies were performed. After confirmation of the diagnosis, each of the seven digital branches of the median nerve on each hand, from the lateral side of the thumb to the lateral side of the ring finger, with the hand in its anatomical position, was stimulated using a Dantec surface stimulating electrode and a Dantec Neuromatic 2000M electromyograph. The stimulating electrodes were placed along each side of the thumb, index and middle finger and lateral side of the ring finger in turn, with the cathode over the proximal phalanx and the anode over the middle phalanx or, in the case of the thumb, the terminal phalanx. The cathode and anode were 2 cm apart. Constant current stimuli of 0.2 msec duration were given at a frequency of llsec. A bipolar surface recording electrode consisting of silver/ silver chloride electrodes covered by saline-soaked pads mounted in Perspex, (interelectrode distance 2 cm), was placed on the wrist just proximal to the distal skin crease. This was fixed with a silicon rubber strap using minimal tension. Filter settings were 20-2000 Hz. Sensory threshold to the stimulus was obtained by asking the subject to report when the stimulus was first perceived. Each nerve was then stimulated supramaximally and the amplitude, latency (measured to the onset of the SNAP), and conduction ve-
602
Digital Nerve Stimulation in CTS
locity (CV) of the averaged SNAP to 10 consecutive stimuli were used in later analysis. Results were divided into those for dominant and nondominant hands. Hand dominance was defined as the hand preferentially used for writing and other everyday activities. Statistical analysis was performed using correlation coefficients. RESULTS
The patients' ages ranged from 29 to 67 years (mean: 44 years) and the age of controls ranged from 26 to 61 years (mean: 41 years). In 11 of the 12 control subjects both hands were studied and in one, only the dominant hand was studied (Table 1). Five controls had SNAP amplitudes less than 10 FV; these subjects tended to be older. Their mean age was 50.2 years (range: 40 to 61 years) whilst that of remaining controls was 35 years (range: 26 to 49 years). Increasing age was associated with a decrease SNAP amplitude from both sides of the thumb and index finger on the dominant hand (correlation coefficients 0.85, 0.85, 0.81 and 0.73 respectively), and for the lateral side of the ring finger on the nondominant hand (correlation coefficient 0.78). There was a positive correlation between increasing age and an increase in sensory threshold for the medial side of the thumb, both sides of the index finger and lateral side of the middle finger (correlation coefficients 0.66, 0.72, 0.65 and 0.72 respectively) on the dominant hand. None of the controls had conduction velocities below 40 m/sec.
Control Subjects.
Patients. All five criteria for the electrophysiological diagnosis of CTS were present in 28 hands (51%). Four criteria were present in 18 hands (33%) and three in 8 hands (14.5%). In one patient the diagnosis of CTS was made on the basis of 2 abnormal findings alone (1.8%). Distal median nerve motor latency was prolonged in 45 hands (82%). Median nerve SNAP amplitude was less than 10 pV in 52 hands (94.5%), and its CV was less than 40 m/sec in 53 hands (96%). Median SNAP amplitude was less than that of the ipsilatera1 ulnar nerve after digital stimulation in 50 hands (91%). The difference between median motor and sensory latencies comparing hands was greater than 0.5 msec in 25 patients (73.5%). In the 12 patients with unilateral CTS, the dominant hand was affected in eight patients and the nondominant hand in four. In one hand a SNAP could not be obtained following stimulation of any
MUSCLE & NERVE
July 1990
Table 1. Normal values for sensory threshold perception, SNAP amplitude and conduction velocity.' Digital nerve IL
Threshold (mA) Dominant hand Mean f SD Range Nondominant hand Mean f SD Range Amplitude (pV) Dominant hand Mean f SD Range Nondominant hand Mean f SD Range Conduction velocity (m/sec) Dominant hand Mean f SD Range Nondominant hand Mean t SD Range
IM
*
11,
1h.A
IllL
IllM
IVL
2.0 0.2 1.7-2.3
3.1 f 1.2 1.9-6.7
3.0 f 0.8 2.0-5.3
2.4 f 0.5 1.6-3.5
2.6 t 0.4 2.1-3.5
2.5 2 9.2 1.9-3.1
2.4 t 0.3 2.0-2.9
2.0 f 0.2 1.6-2.2
2.8 f 0.3 2.4-3.4
2.8 f 0.6 2.2-4.3
2.5 t 0.3 1.9-2.7
2.6 % 0.2 2.4-3.0
2.4 f 0.3 1.7-2.9
2.4 f 0.5 1.7-3.4
13.7 t 5.1 8-23
12.2 f 5.9 5-22
14.2 rt 6.0 7-23
11.3 2 3.6 6-19
15.2 5 5.5 9-25
12.2 f 5.5 7-28
11.6 f 6.2 5- 29
22.3 k 10.2 11-40
20.7 f 8.0 8-35
18.3 t 5.7 8-25
14.8 2 4.6 9-25
17.1 2 5.8 12-30
14.3 f 3.4 9-22
12.0 f 2.4 7-15
50.0 f 6.7 40.7-63.2
47.8 t 5.7 40.7-60.0
54.9 f 6.8 42.2-65.2
53.2 f 6.2 45.0-62.5
51.5 ~ t _5.9 42.2-62.5
50.4 % 6.1 42.2-62.5
51.2 f 5.6 40.9-60.0
48.7 f 4.943.5-60.0
48.4 t 4.2 43.5-55.0
52.8 f 3.6 48.3-58.0
53.5 2 4.1 50.0-62.5
49.7 f 4.0 45.2-57.7
49.6 2 3.4 45.2-55.6
50.7 t 3.7 45.2-56.0
Digital nerves; lL = digital nerve of the lateral side of the first digit, I, = digital nerve of the medial side of the first digit, etc. *From a group of 72 asymptomatic, age-matched women following individual digital nerve stimulation (72 dominant hands; I 1 nondominant hands).
of the digital branches of the median nerve; thus this hand was not included in the study. T h e results of digital nerve stimulation were analyzed with respect to the frequency of abnormalities of threshold, amplitude and CV in CTS (Tables 2 and 3). The upper limit of normal for threshold was taken as 2.5 standard deviations (SD) from the mean in the control population. Sensory threshold measurements proved not to be as sensitive as other means of detecting CTS. A normal threshold was associated with abnormali-
Sensory Threshold.
Table 2. Percentage of digital nerves with at least one abnormal finding, sensory conduction velocity, or amplitude, in 34 women (55 hands) with CTS Digital nerve
Dominant hand (29 hands) Nondominant hand (26 hands)
IL
lM
IIL
IIM
lllL
111M
IvL
98
98
89
85
95
98
92
100
100
77
85
92
96
96
~~
Digital nerves I, = digital nerve of the lateral side of the first digit, I, = digital nerve of the medial side of the first digit, etc
Digital Nerve Stimulation in CTS
ties of sensory conduction velocity or SNAP amplitude in a number of digital nerves (Table 3). Threshold was most commonly affected on the lateral side of the middle finger, where it was abnormal in 71% (dominant) and 65% (nondominant) hands. Threshold was increased in the presence of normal SNAP in only one patient and this for one side of one digit only. Sensory threshold was rarely elevated, in patients with CTS, on the medial side of the thumb or lateral side of the index finger. SNAP Amplitude. Reduction of SNAP amplitude below 10 PV varied from 58% to 78% in digital branches of the median nerve in the dominant hand and from 42% to 85% of nerves in the nondominant hand. If absent responses are included, these figures are raised to 77% to 92% and 42% to 97%, respectively. T h e digital nerve most likely to yield a small amplitude or absent response was that in the lateral side of the ring finger on either hand (92% and 97%; dominant and nondominant hands respectively) and the least likely was that in the lateral side of the index finger (78% and 46%; dominant and nondominant hands respectively). In 9 hands the amplitude of the SNAP evoked from the middle finger was < 10 IJ.V while that
MUSCLE & NERVE
July 1990
603
Table 3. Distribution of abnormal findings foilowing digital nerve stimulation in 34 women (55 hands) with CTS (%) Digital nerve
1,
11,
JIM
IllL
IllM
IVL
54 68 17 86
7 78 10 95
17 68 10 60
23 74 3 57
71 78 10 83
61 74 7 83
27 58 34 61
35 42 0 96
31 69 0 92
19 46 0 62
27 62 4 72
65 54 4 92
35 85 4 92
15 85 12 83
JL
Dominant hand (29 hands) Threshold Amplitude Absent Conduction velocity of SNAP Nondominant hand (26 hands) Threshold Amplitude Absent *Conduction velocity of SNAP
‘Absent responses wefe excluded for the purposes of calculatrng % abnormal conductron velocrbes Digrtal nerves I, = d/g/talnerve of the lateral s/de of the hrst dtgrt, I , = drgrtal nerve of the medral srde of the first digit etc
from the index finger was >10 pV. We did not observe a case where the converse occurred. The CV of the median nerve SNAP at the wrist was preferred to latency because this measure compensates for different hand sizes. Sensory CV was
CARPAL TUNNEL SYNDROME: WHICH FINGER SHOULD BE TESTED? AN ANALYSIS OF SENSORY CONDUCTION IN DIGITAL BRANCHES OF THE MEDIAN NERVE RICHARD A.L. MACDONELL, MBBS, FRACP, MARTIN S. SCHWARTZ, MD, and MICHAEL SWASH, MD, FRCP
Compression of the median nerve in the carpal tunnel causing carpal tunnel syndrome (CTS), is usually an idiopathic disorder, occurring especially in women.576Symptoms include arm pain, often worse at night, and paresthesias in median innervated digits. The nerve supply to these digits comes from the division of the median nerve into four sensory branches and a motor branch to thenar muscles shortly after it exits from the distal end of the carpal tunnel. The most lateral sensory branch becomes th2 digital nerve in the lateral side of the thumb. T h e remaining three subdivide into digital branches supplying adjacent sides of the thumb, index, middle and ring fingers.' CTS may be confirmed electrophysiologically. Characteristic findings are slowing of sensory conduction velocity
From the Department of Neurology, The London Hospital, Whitechapel E l 155. London, United Kingdom (Dr Macdonell. Dr. Swash), and the Department of Neurology, Atkinson Morley's Hospital, Wirnbledon, London, United Kingdom (Dr Schwartz)
and reduction in the amplitude of the sensory nerve action potential (SNAP) between digit and wrist in the median nerve.3*4,10,14*22 These abnormalities may be restricted to only one or two of the nerve's digital branches."." A common method of investigation is to use ring electrodes to stimulate or record from one digit while recording or stimulating, as appropriate, at the wrist. The sensitivity of such testing for CTS may be increased by usin an "inching" technique," by forced wrist or by producing ischemia' of the affected hand. Typically the index or middle fingers have been used, but recent studies suggest that using the thumb or ring finger may improve the sensitivity of electrophysiological d i a g n ~ s i s . " ~ ~ ' ~ ' ~ ~ The aim of this study was to determine the relative frequency of abnormal sensory conduction from the seven digital branches of the median nerve in a group of 34 women with idiopathic CTS.
Dr Macdonell is supported by a Commonwealth Medical Fellowship
MATERIALS AND METHODS
Address reprint requests to Dr. Swash, FRCP, at the Department of Neurology, The London Hospital, Whitechapel, London E l 165, United Kingdom.
Thirty-four consecutive women referred because of clinical symptoms consistent with CTS were studied. In each, the diagnosis was confirmed by routine electrophysiological testing. These women were compared with an age-matched control pop-
Accepted for publication August 7. 1989 CCC 0148-639x/90/070601-06$04.00 0 1990 John Wiley & Sons, Inc.
Digital Nerve Stimulation in CTS
MUSCLE & NERVE
July 1990
601
ulation of 12 women without clinical features of CTS. All patients and control subjects gave informed consent. CTS was bilateral in 22 patients and unilateral in 12. Each patient complained of hand or arm pain, often worse at night, and paresthesias affecting one or more digits. A generalized neuropathy was excluded, in each case, by normal ulnar nerve motor and sensory conduction velocities and normal radial nerve sensory studies in both arms. The electrophysiological criteria used to diagnose CTS were at least two of the following: (1) a distal motor latency from the wrist to thenar eminence > 4.2 msec, (2) SNAP amplitude < 10 pV, (3) SNAP conduction velocity < 40 m/ sec, (4)SNAP amplitude less than that of the ipsilateral ulnar nerve at the wrist, or (5) median motor or sensory latencies at the wrist more than 0.5 msec longer than its counterpart on the opposite hand (gain 500 pV/div). These values are routinely used in our laboratory for the diagnosis of CTS. The latency of the SNAP was measured from the onset of the response. Needle electromyographic studies of the abductor pollicis brevis muscle were not performed. All hands, patients and controls, were warmed prior to testing by seating the patient for 15 minutes in a room at 22"-24"C in which the studies were performed. After confirmation of the diagnosis, each of the seven digital branches of the median nerve on each hand, from the lateral side of the thumb to the lateral side of the ring finger, with the hand in its anatomical position, was stimulated using a Dantec surface stimulating electrode and a Dantec Neuromatic 2000M electromyograph. The stimulating electrodes were placed along each side of the thumb, index and middle finger and lateral side of the ring finger in turn, with the cathode over the proximal phalanx and the anode over the middle phalanx or, in the case of the thumb, the terminal phalanx. The cathode and anode were 2 cm apart. Constant current stimuli of 0.2 msec duration were given at a frequency of llsec. A bipolar surface recording electrode consisting of silver/ silver chloride electrodes covered by saline-soaked pads mounted in Perspex, (interelectrode distance 2 cm), was placed on the wrist just proximal to the distal skin crease. This was fixed with a silicon rubber strap using minimal tension. Filter settings were 20-2000 Hz. Sensory threshold to the stimulus was obtained by asking the subject to report when the stimulus was first perceived. Each nerve was then stimulated supramaximally and the amplitude, latency (measured to the onset of the SNAP), and conduction ve-
602
Digital Nerve Stimulation in CTS
locity (CV) of the averaged SNAP to 10 consecutive stimuli were used in later analysis. Results were divided into those for dominant and nondominant hands. Hand dominance was defined as the hand preferentially used for writing and other everyday activities. Statistical analysis was performed using correlation coefficients. RESULTS
The patients' ages ranged from 29 to 67 years (mean: 44 years) and the age of controls ranged from 26 to 61 years (mean: 41 years). In 11 of the 12 control subjects both hands were studied and in one, only the dominant hand was studied (Table 1). Five controls had SNAP amplitudes less than 10 FV; these subjects tended to be older. Their mean age was 50.2 years (range: 40 to 61 years) whilst that of remaining controls was 35 years (range: 26 to 49 years). Increasing age was associated with a decrease SNAP amplitude from both sides of the thumb and index finger on the dominant hand (correlation coefficients 0.85, 0.85, 0.81 and 0.73 respectively), and for the lateral side of the ring finger on the nondominant hand (correlation coefficient 0.78). There was a positive correlation between increasing age and an increase in sensory threshold for the medial side of the thumb, both sides of the index finger and lateral side of the middle finger (correlation coefficients 0.66, 0.72, 0.65 and 0.72 respectively) on the dominant hand. None of the controls had conduction velocities below 40 m/sec.
Control Subjects.
Patients. All five criteria for the electrophysiological diagnosis of CTS were present in 28 hands (51%). Four criteria were present in 18 hands (33%) and three in 8 hands (14.5%). In one patient the diagnosis of CTS was made on the basis of 2 abnormal findings alone (1.8%). Distal median nerve motor latency was prolonged in 45 hands (82%). Median nerve SNAP amplitude was less than 10 pV in 52 hands (94.5%), and its CV was less than 40 m/sec in 53 hands (96%). Median SNAP amplitude was less than that of the ipsilatera1 ulnar nerve after digital stimulation in 50 hands (91%). The difference between median motor and sensory latencies comparing hands was greater than 0.5 msec in 25 patients (73.5%). In the 12 patients with unilateral CTS, the dominant hand was affected in eight patients and the nondominant hand in four. In one hand a SNAP could not be obtained following stimulation of any
MUSCLE & NERVE
July 1990
Table 1. Normal values for sensory threshold perception, SNAP amplitude and conduction velocity.' Digital nerve IL
Threshold (mA) Dominant hand Mean f SD Range Nondominant hand Mean f SD Range Amplitude (pV) Dominant hand Mean f SD Range Nondominant hand Mean f SD Range Conduction velocity (m/sec) Dominant hand Mean f SD Range Nondominant hand Mean t SD Range
IM
*
11,
1h.A
IllL
IllM
IVL
2.0 0.2 1.7-2.3
3.1 f 1.2 1.9-6.7
3.0 f 0.8 2.0-5.3
2.4 f 0.5 1.6-3.5
2.6 t 0.4 2.1-3.5
2.5 2 9.2 1.9-3.1
2.4 t 0.3 2.0-2.9
2.0 f 0.2 1.6-2.2
2.8 f 0.3 2.4-3.4
2.8 f 0.6 2.2-4.3
2.5 t 0.3 1.9-2.7
2.6 % 0.2 2.4-3.0
2.4 f 0.3 1.7-2.9
2.4 f 0.5 1.7-3.4
13.7 t 5.1 8-23
12.2 f 5.9 5-22
14.2 rt 6.0 7-23
11.3 2 3.6 6-19
15.2 5 5.5 9-25
12.2 f 5.5 7-28
11.6 f 6.2 5- 29
22.3 k 10.2 11-40
20.7 f 8.0 8-35
18.3 t 5.7 8-25
14.8 2 4.6 9-25
17.1 2 5.8 12-30
14.3 f 3.4 9-22
12.0 f 2.4 7-15
50.0 f 6.7 40.7-63.2
47.8 t 5.7 40.7-60.0
54.9 f 6.8 42.2-65.2
53.2 f 6.2 45.0-62.5
51.5 ~ t _5.9 42.2-62.5
50.4 % 6.1 42.2-62.5
51.2 f 5.6 40.9-60.0
48.7 f 4.943.5-60.0
48.4 t 4.2 43.5-55.0
52.8 f 3.6 48.3-58.0
53.5 2 4.1 50.0-62.5
49.7 f 4.0 45.2-57.7
49.6 2 3.4 45.2-55.6
50.7 t 3.7 45.2-56.0
Digital nerves; lL = digital nerve of the lateral side of the first digit, I, = digital nerve of the medial side of the first digit, etc. *From a group of 72 asymptomatic, age-matched women following individual digital nerve stimulation (72 dominant hands; I 1 nondominant hands).
of the digital branches of the median nerve; thus this hand was not included in the study. T h e results of digital nerve stimulation were analyzed with respect to the frequency of abnormalities of threshold, amplitude and CV in CTS (Tables 2 and 3). The upper limit of normal for threshold was taken as 2.5 standard deviations (SD) from the mean in the control population. Sensory threshold measurements proved not to be as sensitive as other means of detecting CTS. A normal threshold was associated with abnormali-
Sensory Threshold.
Table 2. Percentage of digital nerves with at least one abnormal finding, sensory conduction velocity, or amplitude, in 34 women (55 hands) with CTS Digital nerve
Dominant hand (29 hands) Nondominant hand (26 hands)
IL
lM
IIL
IIM
lllL
111M
IvL
98
98
89
85
95
98
92
100
100
77
85
92
96
96
~~
Digital nerves I, = digital nerve of the lateral side of the first digit, I, = digital nerve of the medial side of the first digit, etc
Digital Nerve Stimulation in CTS
ties of sensory conduction velocity or SNAP amplitude in a number of digital nerves (Table 3). Threshold was most commonly affected on the lateral side of the middle finger, where it was abnormal in 71% (dominant) and 65% (nondominant) hands. Threshold was increased in the presence of normal SNAP in only one patient and this for one side of one digit only. Sensory threshold was rarely elevated, in patients with CTS, on the medial side of the thumb or lateral side of the index finger. SNAP Amplitude. Reduction of SNAP amplitude below 10 PV varied from 58% to 78% in digital branches of the median nerve in the dominant hand and from 42% to 85% of nerves in the nondominant hand. If absent responses are included, these figures are raised to 77% to 92% and 42% to 97%, respectively. T h e digital nerve most likely to yield a small amplitude or absent response was that in the lateral side of the ring finger on either hand (92% and 97%; dominant and nondominant hands respectively) and the least likely was that in the lateral side of the index finger (78% and 46%; dominant and nondominant hands respectively). In 9 hands the amplitude of the SNAP evoked from the middle finger was < 10 IJ.V while that
MUSCLE & NERVE
July 1990
603
Table 3. Distribution of abnormal findings foilowing digital nerve stimulation in 34 women (55 hands) with CTS (%) Digital nerve
1,
11,
JIM
IllL
IllM
IVL
54 68 17 86
7 78 10 95
17 68 10 60
23 74 3 57
71 78 10 83
61 74 7 83
27 58 34 61
35 42 0 96
31 69 0 92
19 46 0 62
27 62 4 72
65 54 4 92
35 85 4 92
15 85 12 83
JL
Dominant hand (29 hands) Threshold Amplitude Absent Conduction velocity of SNAP Nondominant hand (26 hands) Threshold Amplitude Absent *Conduction velocity of SNAP
‘Absent responses wefe excluded for the purposes of calculatrng % abnormal conductron velocrbes Digrtal nerves I, = d/g/talnerve of the lateral s/de of the hrst dtgrt, I , = drgrtal nerve of the medral srde of the first digit etc
from the index finger was >10 pV. We did not observe a case where the converse occurred. The CV of the median nerve SNAP at the wrist was preferred to latency because this measure compensates for different hand sizes. Sensory CV was
