Two cases of thyrotoxicosis with severe myalgia as early presentation

Myalgia is rare in acquired muscle diseases other than inflammatory myopathies. Thyrotoxic myopathy is usually painless. We reported here two patients with acute onset of thyrotoxicosis presenting with severe myalgia and mild proximal weakness. No other etiologies responsible for the myalgia was identified. The symptoms resolved in parallel with the achievement of euthyroidism, supporting hyperthyroidism as the cause of myalgia. Painless myopathy was well known to be related to hyperthyroidism, but the myalgia is scarcely reported. We summarized the previous literatures to elucidate the thyroid hormone effect on the muscle, such as increased energy expenditure in hyperthyroidism. We hypothesized that the myalgia is related to the muscle injury by the energy failure during an acute onset of thyrotoxicosis.