Myopathy in hyperthyroidism as a consequence of rapid reduction of thyroid hormone: A case report

RATIONALE: Myalgia and elevated creatine kinase (CK) are occasionally observed during the treatment of hyperthyroid patients. Relative hypothyroidism resulted from rapid thyroid hormone reduction had been promoted as a plausible cause of these myopathic changes, however rarely reported. PATIENT CONCERNS: We hereby presented a 20-year-old female with Grave's disease, who developed myopathy and elevated CK during rapid correction of thyroid hormone. DIAGNOSES: Relative hypothyroidism-induced myopathy. INTERVENTIONS: Antithyroid drug (ATD) dosage was reduced without levothyroxine replacement. OUTCOMES: The muscular symptoms were recovered with CK level returned to normal after adoption of the euthyroid status. LESSONS: Differentiation of relative hypothyroidism from other causes of myopathy, especially with the effect of ATD, is important for clinical practice, although difficult in many cases.