Cores in hypothyroid myopathy: a clinical, histological and immunofluorescence study.

Fifteen patients with primary hypothyroidism were evaluated neurologically. Needle biopsies of skeletal muscle were obtained using a Bergstrom needle. In 73% of the patients, cores were identified histologically and by electron microscopy in the skeletal muscle of these patients. The presence of cores correlated with the severity of hypothyroidism, muscle hypertrophy, cramps and the duration of the hypothyroid state. There was no significant correlation with muscle weakness. Immunofluorescence studies with N-CAM antibodies demonstrated staining of the sarcolemma, cytoplasm and central regions (cores) in the hypothyroid muscle. These imply that the presence of cores in hypothyroid myopathy is due to reactivation of embryonic proteins that disrupt skeletal muscle architecture.