Central changes in hypothyroid myopathy: a case report.

A muscle biopsy from a patient with hypothyroid myopathy showed striking central changes. "Cores" were seen in most type 1 fibers with oxidative enzyme preparations. Electron microscopy of these areas revealed Z disc streaming, myofilament disruption, and absent mitochondria. The myopathy rapidly improved with thyroxine treatment. This biopsy is of interest, as numerous "cores" have not previously been reported in hypothyroid myopathy.