and Mario Di Napoli1
(1)
Neurological Service, S. Camillo de’ Lellis General Hospital, Rieti, Italy
Original Settings
Sensitivity was 15 μV/division, sweep speed was 2 ms/division, duration of pulse was 0.1–0.4 ms, and the machines used were a Tektronix type 122 preamplifier and a Tektronix type 564 B storage oscilloscope; low frequency filter, high-frequency filter and rate of pulse were not specified.
Position
This study was performed in the supine position.
Recording
Following the orthodromic method [1], signals were recorded using surface electrodes (10-mm disks or standard rings) from the median and ulnar nerves separately (Fig. 1). For the median nerve (R1) and ulnar nerve (R2), the active recording electrodes (A) were placed proximal to the distal crease at the wrist, on the median and ulnar trunks, respectively. No fixed distances were mentioned in the text. The cathodes were placed proximally. Great care was taken to prevent the spread of stimulus to the adjacent digits by covering them with a nonconducting adhesive plaster, as it was found that a spread of stimulus through contact of stimulating electrodes with the adjacent digits could significantly increase the size of the sensory potential. Ground (G) electrode position was not specified in the report; the figure shows the ground electrode placed on the palm.
Fig. 1
Orthodromic sensory nerve action potentials (SNAPs) recorded at the wrist, stimulation of digit II (upper trace) and digit V (lower trace)
Stimulation
Stimulation was applied over the median and ulnar nerves to the base of digit II (index finger) and digit V (little finger), respectively. The cathodes were placed distally on the proximal interphalangeal joint of digit II and digit V for median (S1) and ulnar (S2) stimulations, respectively. The authors used only supramaximal stimulation with a duration of 0.1–0.4 ms.
Measurements
Onset latency (ms) was measured from the stimulus onset to the onset of the negative deflection of the evoked sensory nerve action potential (SNAP); peak latency (ms) was measured from the stimulus onset to the peak of the negative deflection of SNAP. The onset latency was used for the purpose of estimation of sensory nerve conduction velocity (NCV). The amplitudes (μV) of the sensory potentials were measured from the negative peak to the positive peak of the SNAP (peak to peak amplitude). All examinations were performed in a room with a constant ambient temperature of 23–25 °C. Median to ulnar amplitude ratio (Amp Rat) was determined by dividing the median digital sensory amplitude (digit II stimulation) by the ulnar digital sensory amplitude (digit V stimulation). Normal values (Table 1) were obtained from 50 healthy women (age range 30–60 years). The authors also studied 15 patients (Table 2) with a clinical diagnosis of carpal tunnel syndrome (CTS) – 7 bilateral, 22 affected hands (all women, age range 31–60 years).
Median – SNCV (m/s) | Mean ± SD | Range |
|---|---|---|
Digit II–wrist | 52.3 ± 4.1 | 44–59 |
Median – peak to peak amplitude (μV) | Range |
|---|---|
Wrist–digit II | 9–48 |
Ulnar – peak to peak amplitude (μV) | Range |
|---|---|
Wrist–digit V | 7.5–33 |
Median–ulnar – amplitude ratio | Limit of normal | Range |
|---|---|---|
– All subjects – | ≥1.1 | 1.1–2.4 |
Median onset latency (ms) – digit II–wrist | Right hand | Left hand |
|---|---|---|
Patient (40 years) | 2.9 | 2.5 |
Patient (42 years) | 3.2 | 2.9 |
Patient (50 years) | 2.4 | 2.5 |
Patient (59 years) | 4.6 | – |
Patient (45 years) | 2.9 | – |
Patient (37 years) | 1.8 | – |
Patient (37 years) | 2.3 | – |
Patient (60 years) | 3.3 | – |
Patient (35 years) | 3.2 | 2.8 |
Patient (37 years) | 3.0 | – |
Patient (37 years) | – | – |
Patient (31 years) | – | – |
Patient (42 years) | 2.8 | 3.4 |
Patient (45 years) | 3.2 | – |
Patient (43 years) | 3.5 | 3.3 |
Median peak latency (ms) – digit II–wrist | Right hand | Left hand |
|---|---|---|
Patient (40 years) | 4.0 | 3.1 |
Patient (42 years) | 4.2 | 3.8 |
Patient (50 years) | 3.0 | 3.4 |
Patient (59 years) | 5.5 | – |
Patient (45 years) | 3.7 | – |
Patient (37 years) | 2.4 | – |
Patient (37 years) | 2.8 | – |
Patient (60 years) | 4.5 | – |
Patient (35 years) | 4.4 | 3.2 |
Patient (37 years) | 3.9 | – |
Patient (37 years) | – | – |
Patient (31 years) | – | – |
Patient (42 years) | 3.3 | 4.1 |
Patient (45 years) | 3.9 | – |
Patient (43 years) | 4.4 | 4.2 |
Median peak amplitude (μV) – digit II–wrist | Right hand | Left hand |
|---|---|---|
Patient (40 years) | 6.0 | 10.5 |
Patient (42 years) | 8.0 | 18.0 |
Patient (50 years) | 10.5 | 16.5 |
Patient (59 years) | 3.8 | – |
Patient (45 years) | 16.5 | – |
Patient (37 years) | 13.5 | – |
Patient (37 years) | 16.5 | – |
Patient (60 years) | 4.0 | – |
Patient (35 years) | 8.0 | 18.0 |
Patient (37 years)
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