An Unusual myopathy: speckled muscle fibers due to enlarged mitochondria

We report a 52-year-old woman who presented with a 6-month history of proximal muscle weakness, elevated serum creatine kinase, and myopathic pattern on electromyography (EMG). Histology of the muscle shows a speckled pattern due to clustering of enlarged mitochondria. The pathology resembles that of selenium deficiency. The patient was found to have borderline low serum selenium and also low vitamin D and thyroid-stimulating hormone. The cause of this unusual myopathy is probably multifactorial. This case is important because the unusual pathological picture represents a potentially treatable myopathy. In addition, we hope that publication of the complex clinical and biochemical abnormalities of this case, in conjunction with other case reports, may facilitate future elucidation of muscle mitochondrial function and dysfunction. Muscle Nerve, 2007 Most muscle diseases produce one of a limited range of stereotypic pathological responses in the muscle fibers. We report a case of myopathy with a clinical picture similar to polymyositis but with distinct and unusual features on light and electron microscopy. The histopathological features are similar to a previously reported patient with selenium deficiency after long-term total parenteral nutrition. Although the present patient did have slightly reduced serum selenium this is unlikely to have been the sole cause of the myopathy. The complex and multiple influences on selenium metabolism and mitochondrial pathology are discussed with particular reference to dietary and endocrine factors.