Typical herpes zoster(HZ) presents as a vesicular eruption along sensory dermatomes. It is less well known that HZ cause motor paralysis. The occurrence of motor deficit complicated with HZ has been reported since 1866, but the frequency of motor
involvement is very variable, ranging 0.5 to 31.0%. There are few electromyographic studies in HZ patients who ae not complicated with motor symptom. The purpose of this study is to investigate the extent of motor involvement in thoracic HZ, by
means of
electromyography(EMG). We performed EMG of paraspinal muscles of several segments around involved dermatomal level, ipsilateral to skin lesions. A total of 81 patients(31 men, 50 women ; mean age : 53.4 ranging 14 to 85 years) were subjected, who
had no
clinical weakness. Mean interval was 9.7 days between skin eruption and EMG studies. The motor involvement revealed by denervation potentials on EMG study was seen in 44(54.3%) of 81 patients. There was no significant difference between both
sexes,
although the rate of motor involvement was slightly higher in men than in women. There was no statistical relationship between age and motor involvement. In 44 cases with motor involvement on EMG, denervation potentials were observed more widely
beyond
the involved dermatomes.
In conclusion, subclinical motor involvement is rather frequent accompaniment with thoracic HZ, although clinical motor symptom is very rare. This study also suggests that motor involvement, when occurs, tend to be wider in distribution than
dermatomal
involvement and could develop at the same time as the onset to skin lesion or even earlier.
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