Wrist – Digit IV | Neupsy Key

and Mario Di Napoli¹

(1)

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

Original Settings

Sensitivity was 20 μV/division, sweep speed was 1 ms/division, duration of pulse was 0.05 ms, and the machines used were a TECA TE-4 (34 subjects), a TECA model M (1 subject), and neurodiagnostic (2 subjects). 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 antidromic method [1], signals were recorded using ring electrodes, 14 cm distally from the wrist to digit IV (Fig. 1). The active electrode (A) was placed at the base of digit IV. The reference (R) was placed on the junction between the middle phalanx and the distal phalanx, 4 cm distal to the active electrode. Ground (G) was placed on the palm of the hand. Median (R1) and ulnar (R2) nerve recordings were made separately.

Fig. 1

Antidromic sensory nerve action potentials (SNAPs) recorded to digit IV, stimulation of the wrist: median nerve (upper trace) and ulnar nerve (lower trace)

Stimulation

Stimulation was applied proximally to the distal wrist crease, at the wrist 14 cm proximally to the recording electrode (A), on two different points: on the median nerve (S1), between the tendons of the flexor carpi radialis (FCR) and the palmaris longus (PL) muscles (ideally proximal to the distal wrist crease), and on the ulnar nerve (S2), just lateral to the tendon of the flexor carpi ulnaris (FCU) muscle. A monopolar pin was used for stimulation; the authors compared the needle electrode stimulation (used for 34 subjects) with the surface stimulation for 3 subjects. There was no difference in the results whether surface or needle stimulation was used.

Median and ulnar nerve stimulations were made separately. The stimulus was gradually increased until the response was a maximum using 0.05 ms of duration of the current pulse.

Measurements

Distal onset latency (ms) was measured from the onset of the stimulus to the onset of the negative deflection of the evoked sensory nerve action potential (SNAP). Differences between the median and ulnar distal latencies at various ages and comparing the dominant to nondominant hands were reported. Hand temperature, determined using a surface thermistor over the midpalm, was found to be 30 °C or greater in all subjects. The authors studied 37 normal subjects (Table 1), divided into 4 groups according to age (18 women, 19 men).

Table 1

Normal values [1]

Median–ulnar nerves Distal latency difference (ms)	Limit of normal
All subjects	≤0.6

Median nerve–distal latency (ms) in the dominant hand	Mean ± SD	Mean ± 2 SD
Age range 20–29 (10 subjects)	3.1 ± 0.18	3.5
Age range 30–39 (10 subjects)	2.96 ± 0.15	3.3
Age range 40–49 (7 subjects)	3.19 ± 0.27	3.7
Age range 50–59 (10 subjects)	3.30 ± 0.23	3.8
All subjects	3.14 ± 0.24	3.6

Median nerve–distal latency (ms) in the nondominant hand	Mean ± SD	Mean ± 2 SD
Age range 20–29 (10 subjects)	3.15 ± 0.18	3.5
Age range 30–39 (10 subjects)	2.96 ± 0.22	3.4
Age range 40–49 (7 subjects)	3.19 ± 0.30	3.8
Age range 50–59 (10 subjects)	3.28 ± 0.24	3.8
All subjects	3.11 ± 0.32	3.7

Ulnar nerve–distal latency (ms) in the dominant hand	Mean ± SD	Mean ± 2 SD
Age range 20–29 (10 subjects)	3.11 ± 0.15	3.4
Age range 30–39 (10 subjects)	2.89 ± 0.20	3.3
Age range 40–49 (7 subjects)	3.04 ± 0.20	3.4
Age range 50–59 (10 subjects)	3.08 ± 0.23	3.5
All subjects	3.03 ± 0.21	3.5

Ulnar nerve–distal latency (ms) in the nondominant hand	Mean ± SD	Mean ± 2 SD
Age range 20–29 (10 subjects)	3.06 ± 0.16	3.4
Age range 30–39 (10 subjects)	2.91 ± 0.20	3.3
Age range 40–49 (7 subjects)	3.19 ± 0.29	3.8
Age range 50–59 (10 subjects)	3.12 ± 0.24	3.6
All subjects	3.01 ± 0.32	3.6

Comment

For Johnson et al. [1] the difference between the median and the ulnar sensory latency to digit IV was, in all instances, less than 0.6 ms, and 93 % of all the hands studied had a difference between the median and ulnar latencies of 0.3 ms or less. Comparison of the median and the ulnar latencies in the dominant versus nondominant hands revealed no significant differences.

Jackson and Clifford [2] using a TECA model TD10A electromyograph (factory-set filter combination: 20 Hz–2 kHzfor surface sensory recordings and 2 Hz–10 kHz for surface motor recordings) performed five different tests on 38 healthy (Table 2) volunteers (Group A, 38 hands, 76 % women, mean age 42.2 ± 12.1 years, age range 21–69 years) and 123 patients (Table 3) having symptoms of carpal tunnel syndrome (CTS). 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), the most severe cases of median nerve compression at the wrist, demonstrating abnormal NCS and abnormal EMG.

Table 2

Normal values [2]

Median–ulnar nerves Distal latency difference (ms)	Mean ± SD	Range	Limit of normal (−2 SD)
Onset latency – all subjects	0.13 ± 0.15	−0.08 to 0.46	≤0.43
Peak latency – all subjects	0.09 ± 0.13	−0.14 to 0.52	≤0.35

Table 3

Pathological values [2]

Median–ulnar nerves Distal latency difference (ms)	Mean ± SD	Range	Limit of normal (−2 SD)
Group B	0.41 ± 0.36	0.0–2.90	≤0.35
Group C	1.72 ± 1.10	0.30–5.30	≤0.35
Group D	2.39 ± 1.77	0.40–6.30	≤0.35

In 1990, Charles et al. [3] confirmed the specificity of the antidromic stimulation of the ring finger (digit IV) in early electrodiagnosis of mild CTS and compared its sensitivity to that of standard parameters, such as distal motor latency, or orthodromic sensory nerve conduction to the index finger (digit II). They performed nerve conduction studies using a 21P electromyograph (sensory filter was set at 2 Hz–2.5 kHz) on 60 healthy (Table 4) subjects (100 hands, 20 hands from 12 men, age range 31–61 years and mean age 43.2 years; 80 hands from 48 women, age range 23–76 years and mean age 45.5 years). They studied also 158 consecutive patients (Table 5) referred to their department for CTS (224 symptomatic hands, 37 hands from 26 men, age range 20–60 years and mean age 43.2 years; 187 hands from 132 women, age range 24–64 years and mean age 47.9 years).

Table 4

Normal values [3]

Only gold members can continue reading. Log In or Register to continue