Abstracts of the 8th Meeting of the Italian Peripheral Nerve Study Group: 67

Abstract

Sporadic inclusion body myositis (IBM) is a late onset idiopathic inflammatory myopathy, characterized by rimmed vacuoles and cytoplasmic or nuclear tubulofilamentous inclusions. Clinical features are proximal and/or distal weakness, frequent muscle atrophy, hyporeflexia and poor responsiveness to steroid treatment. The involvement of peripheral nerve in both sporadic and familial IBM is a debated issue. Among six cases (five men; age range: 65–82 yrs.) of muscle biopsy proven sporadic IBM, we found variable neuropathic changes. Myogenic/neurogenic mixed EMG pattern was detected in four patients. Sensory and motor nerve conduction studies showed abnormalities consistent with axonal multiple mononeuropathy in three and with axonal polyneuropathy in two patients, whereas one subject had no neurogenic findings. However, the degree of peripheral nerve impairment was usually mild and not related to severity of myopathy. Sural nerve biopsy was performed in the case with more prominent clinical and electrophysiological polyneuropathy. Moderate homogeneous loss of myelinated fibers, with recurrent regeneration clusters and atrophic/degenerating axons were observed. No segmental demyelination was present. In spite of marked inflammatory changes in muscle, neither mononuclear cell infiltrates nor filamentous inclusions were detected in nerve. Similarly, whereas paracrystalline mitochondrial inclusions were observed in muscle, minor but recurrent mitochondrial changes were detected in nerve. Muscle mitochondrial abnormalities have been reported about twice in IBM compared with other inflammatory myopathies. A relation of this finding with high incidence of associated peripheral neuropathy in IBM and mitochondrial myopathies has been hypothesized. On the other hand, the follow‐up of our patients shows improvement of nerve conduction values in clinically responders to intravenous immunoglobulin treatment, suggesting a significant role of immune processes for the pathogenesis of nerve damage in IBM.