A case of hypokalemic myopathy associated with transient hypothyroidism

A case of transient hypothyroidism in the course of hypokalemic myopathy is reported. A 69-year-old woman had severe muscle weakness and marked potassium deficiency associated with alkalosis during treatment with thiazide diuretics. The cause of muscle weakness proved to be hypokalemic myopathy confirmed by clinical findings and muscle biopsy. After the episode of hypokalemic myopathy, serum levels of thyroid hormone were lowered (T4; 3.8 micrograms/dl, T3; 54 ng/dl) and that of TSH was elevated (25.1 microU/ml). Antithyroid microsomal antibody was positive (1:25600) and anti-thyroglobulin antibody was negative. About one month after potassium supplement, her thyroid functions returned to normal, along with normalization of serum potassium level. This is the first documented case report of hypokalemic myopathy accompanied by transient hypothyroidism in a patient with autoimmune thyroiditis. We suggest that this transient hypothyroidism might be induced by hypokalemia during the course of autoimmune thyroiditis.