Motor Involvement in Zoster is Often Clinically Silent
March 1, 1998
Motor Involvement in Zoster is Often Clinically Silent
Source: Haanpaa M, et al. Motor involvement in acute herpes zoster. Muscle Nerve 1997;20:1433-1438.
Herpes zoster typically erupts unilaterally in a single dermatome, with thoracic (50%) and trigeminal (18%) regions affected most commonly (Thomas JE, Howard FM. Neurology 1972;22:459-466). Weakness affecting the corresponding myotomal muscles is reported in up to 30%, but its extent and relationship to the rash are uncertain. In a sample of 40 patients with acute herpes zoster without clinical weakness, 21 (53%) demonstrated motor involvement, documented by abnormal needle electromyography (EMG) showing positive sharp waves and high frequency discharges. Findings were confined to the affected segmental level in 43%, whereas 57% demonstrated widespread findings, including bilateral involvement, in six, of paraspinal or segmental limb muscles, or both. Follow-up EMG, 10-20 weeks later, showed worsening of the findings in five (13%) despite good clinical recovery. No correlation was seen between the extent of EMG findings and the severity of the eruption, pain, or development of postherpetic neuralgia. Subclinical motor involvement is common in herpes zoster, but documenting its presence is irrelevant to the patient. For better or worse, assume it is there. EMG studies, as a rule, remain unnecessary. -mr
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