Chronic Myopathy as the Initial Manifestation of Thyrotoxicosis: A Report of 2 Cases

Abstract Introduction: Rarely, hyperthyroidism will initially present with chronic myopathy characterized by progressive and sometimes fluctuating proximal muscle weakness, along with elevated creatine kinase and myopathic pattern in the electromyogram, mimicking other muscle and neuromuscular junction disorders with poorer prognosis. Cases: Here, we present 2 young patients who complained of 1–4 months duration of chronic proximal muscle lower extremity weakness, supported by elevated creatine kinase and myopathic pattern in electromyogram, who later found to have markedly low thyroid-stimulating hormone, high free T3 and free T4, enlarged thyroid gland on ultrasound, and elevated anti–thyroid-stimulating hormone receptor antibody, characteristic of Grave disease. Conclusions: Although rare, thyrotoxicosis should always be ruled out in a patient with chronic myopathy because this has better prognosis than other primary muscle conditions presenting similarly.