[Varicella-zoster virus-associated spinal myoclonus without skin lesions]

A 50-year-old woman was admitted to our hospital because of abnormal involuntary movement of upper abdomen. Three months before admission, she had suffered from left lateral chest pain without skin lesions for one week. The neurological examination on admission revealed myoclonus of upper abdomen, and hyperalgesia and thermohyperesthesia from T4 to T9. There was no weakness, the tendon reflexes were symmetrical and the plantar responses were flexor. The surface EMG disclosed the symmetrical, synchronous contractions of m. rectus abdominis and m. obliques externus abdominis. This spinal myoclonus reduced during sleep. The EEG, CT and MRI showed no abnormalities. Serum varicella-zoster virus (VZV) titers increased significantly on follow-up examinations. Clonazepam, 1.5 mg daily was effective in this patient. The myoclonus spontaneously disappeared without clonazepam in six weeks after onset, and at the same time the sensory disturbance also improved. From the neurological findings and clinical course, we consider this spinal myoclonus was probably elicited by involvement of the inhibitory interneurons of the dorsal horns, due to immune response to latent VZV infection but not to direct neuronal destruction by VZV. Spinal myoclonus should be recognized as the spectrum of neurological disease associated with VZV even in the absence of skin lesions.