[A study of motor unit number estimation by multiple point stimulation in patients with Hirayama disease]

To explore the significance of motor unit number estimation (MUNE) by using multiple point stimulating technique to evaluate patients with Hirayama disease (HD).

Multiple point stimulating technique was used to estimate the motor unit number of abductor pollicis brevis and abductor digiti minimi in 35 normal subjects [14 - 33 years old, mean (20.9 ± 4.0) years old, 33 men and 2 women] without nerve and muscle disease and 69 patients definitely diagnosed as HD [16 - 35 years old, mean (21.46 ± 6.61) years old, 67 men and 2 women]. The differences between the two groups were examined by Fisher's exact test and t test.

There were 42 patients with atrophy and 27 patients with normal clinical manifestation of left hand. For right hand there were 54 patients with atrophy and 15 normal. For controls, the MUNE value of left abductor pollicis brevis was 226.97 ± 30.59, while that of right side was 228.31 ± 25.35. The MUNE value of left abductor digiti minimi was 237.43 ± 30.78, while that of right side was 240.20 ± 37.73. For HD patients, the MUNE of left abductor pollicis brevis and abductor digiti minimi was 145.66 ± 126.10 (t = 5.07, P < 0.01) and 102.20 ± 112.67 (t = 9.31, P < 0.01) respectively, while those of right hand was 149.72 ± 117.80 (t = 5.31, P < 0.01) and 64.23 ± 69.27 (t = 16.76, P < 0.01) respectively. MUNE of left abductor digiti minimi in 17 patients that was below 200 among 27 patients with normal clinical manifestation (χ(2) = 9.57, P = 0.002). MUNE of right abductor digiti minimi in 12 patients that was below 200 among 15 patients with normal clinical manifestation (χ(2) = 4.64, P = 0.03).

The differences of MUNE values by multiple point stimulating technique between the normal subjects and the HD patients is significant, which suggests this method is very useful to evaluate HD in the early state.