Hypothyroid myopathy with a strikingly elevated serum creatine kinase level

Although serum creatine kinase (CK) levels are frequently modestly elevated in patients with hypothyroid myopathy, elevations in serum CK to the levels usually seen in inflammatory myopathies or dystrophies are rare. We report a patient with progressive proximal weakness and a serum CK level of over 29,000 IU/L, in whom subsequent laboratory evaluation identified profound hypothyroidism. Thyroid hormone replacement therapy resulted in resolution of clinical symptoms and a marked reduction in the serum CK level. Such a high serum CK level in a patient with hypothyroidism underscores the importance of assessing thyroid function in patients with weakness, regardless of serum CK levels, even when systemic symptoms and signs of hypothyroidism are minimal or absent.