Wrist – Digit I | Neupsy Key

and Mario Di Napoli¹

(1)

Neurological Service, S. Camillo de’ Lellis General Hospital, Rieti, Italy

Original Settings

Sensitivity, low-frequency filter, high-frequency filter, sweep speed, duration of pulse, rate of pulse, and the machine used were not specified.

Position

This study was performed in the supine position.

Recording

Following the antidromic method [1], ring electrodes were placed over the digit I (thumb) to record median (R1) and radial (R2) sensory nerve action potentials (SNAPs). The active electrode (A) was placed at the base of the digit I, 10 cm from the stimulation points for the median (S1) and radial (S2) nerves at the wrist. The reference (R) was placed on the distal junction between the proximal phalanx and the distal phalanx. Ground (G) electrode position was not specified in the report; the figure shows the ground electrode placed on the palm. Median (R1) and radial (R2) nerve recordings were made separately (Fig. 1).

Fig. 1

Antidromic sensory nerve action potentials (SNAPs) recorded to the digit I, stimulation at the wrist: median nerve (upper trace) and radial nerve (lower trace)

Stimulation

Stimulation was applied at the wrist (S1, S2), 10 cm proximally to the recording electrode (A) on the median (R1) and radial (R2) nerves. On the median nerve (S1), stimulation was applied proximally to the center of the distal wrist crease and between the tendons of the flexor carpi radialis (FCR) and the palmaris longus (PL) muscles. On the radial nerve (S2), the stimulator was placed on the dorsolateral surface of the wrist. Authors used the monopolar pin for stimulating both the median and radial nerves; they used the same technique well described in a previous work [2]. Standard surface stimulation can be used. Median and radial nerves were stimulated separately.

Measurements

Peak latency (ms) was measured from the onset of the stimulus to the peak of the negative deflection of the sensory nerve action potential (SNAP). Negative peak amplitude (μV) was measured from the isoelectric line to the peak of the negative deflection of the SNAP. Proximal palm skin temperature was between 33.5 and 34.5 °C in all individuals. Normal values (Table 1) were recorded in 78 healthy subjects (23 women and 55 men, age range 20–79 years).

Table 1

Normal values [1]

Peak latency (ms)	Mean ± SD	Range
Median nerve	2.5 ± 0.2	2.0–2.9
Radial nerve	2.4 ± 0.2	1.9–2.8

Amplitude (μV)	Mean ± SD
Median nerve	30 ± 2.0
Radial nerve	12 ± 1.0

Peak latency difference (ms)	Mean ± SD
Median–radial nerves	<0.5

Comment

Johnson et al. [1] chose a 10 cm measurement because the radial nerve becomes superficial and at this point, courses from the volar lateral wrist surface to the dorsolateral aspect. They performed a test on 78 normal subjects (55 men and 23 women, age range 20–79 years) and on a group of 20 patients with symptoms of CTS and the antidromic median sensory latencies to digit III at 14 cm of greater than 4 ms and median motor latencies of greater than 4.3 ms. The median–radial latency difference (MRLD) was calculated subtracting the radial to median peak latencies (ms). Johnson et al. [1] determined that 93 % of the healthy individuals had a latency of less than 0.5 ms difference between the median and the radial nerves, while all individuals with carpal tunnel syndrome (CTS) had differences in radial and median antidromic latencies of 1 ms or greater to digit I (10 cm). A transcription error probably occurred for the mean median latency SD value reported in the abstract of the article; 2.5 ± 0.3 was the value reported, while in the text, 2.5 ± 0.2 was reported.

Jackson and Clifford [3] using a TECA model TD10A electromyograph (factory-set filters combination: 20 Hz–2 kHz for surface sensory recordings and 2 Hz–10 kHz for surface motor recordings) performed five different tests on 38 hands (Table 2) of 38 normal volunteers (Group A – 76 % women, mean age 42.2 ± 12.1 years, age range 21–69 years) and 123 patients having symptoms of CTS (Table 3). After the electrodiagnostic examination that included both nerve conduction studies (NCS) and electromyography (EMG), the patients were subdivided into three groups: Group B (43 hands from 40 subjects, 90 % women, mean age 43.5 ± 11.8 years, age range 21–66 years), the mildest cases of median compression at the wrist, having normal findings on conventional NCS and EMG; Group C (55 hands from 53 subjects, 75 % women, mean age 53.8 ± 12.8 years, age range 31–82 years), more severe cases of median compression at the wrist, demonstrating abnormal conventional NCS, but normal EMG; and Group D (33 hands from 30 subjects, 83 % women, mean age 62.7 ± 17.3 years, age range 23–85 years), most severe cases of median nerve compression at the wrist, demonstrating abnormal NCS and abnormal EMG.

Table 2

Normal values [3]

Median–radial nerves	Mean ± SD	Range	Limit of normal (−2SD)
Distal latency difference (ms)	Mean ± SD	Range	Limit of normal (−2SD)
Onset latency	0.08 ± 0.12	−0.16 to 0.28	≤0.32
Peak latency	0.13 ± 0.12	−0.24 to 0.28	≤0.37

Table 3

Pathological values [3]

Median–radial nerves – peak latency (ms)	Mean ± SD	Range	Limit of normal (−2SD)
Group B	0.33 ± 0.26	−0.20 to 0.80	≤0.37
Group C	1.17 ± 0.69	0.16–2.80	≤0.37
Group D	1.64 ± 1.14	0.40–3.90	≤0.37

Sheu et al. [4] performed a median–radial digit I comparative study (D1M–D1R) in 136 control hands (Table 4) from 136 healthy subjects (82.4 % were women, age range 21–79 years, mean age 49.67 years) and in 235 hands from 153 patients with different severity of CTS (131 hands from 104 patients with mild CTS were also studied, 84.6 % were women, age range 28–74 years, mean age 49.25 years). Authors used a Medelec Synergy electromyograph (sensitivity was 10 μV/division, low-frequency filter was 20 Hz, high-frequency filter was 2 kHz, sweep speed was 1 ms/division, and duration of pulse was 0.05–0.1 ms), the sensory potentials were recorded by averaging 16 responses, and skin temperatures were maintained at 32–34 °C during the conduction studies. They used a 10 cm fixed distance between recording (to the digit I) and stimulating electrodes (at the wrist) for both median and radial nerves.

Table 4

Normal values [4]

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