Skeletal muscle microvascular alterations in euthyroid and hypothyroid patients with autoimmune thyroid disease.

An electron microscopic study of skeletal muscle biopsies from euthyroid and hypothyroid patients with autoimmune thyroid disease (ATD) showed the existence of capillary alterations and a mononuclear cell infiltrate. Microvascular abnormalities included thickening and lamination of basement membrane, endothelial proliferation with progressive lumen occlusion, and hypertrophied pericytes. Capillary degeneration was also observed. Macrophages, and scarce lymphocytes and mast cells formed the cell infiltrate. This pathological picture is similar to that found in the muscular compromise of other autoimmune diseases, particularly Graves' hyperthyroidism. This study shows that patients with ATD may have skeletal muscle capillary abnormalities that could probably be related to autoimmunity and are independent of thyroid functional status.