Thyrotropin-secreting pituitary adenoma presenting as hypokalemic periodic paralysis

Thyrotropin (TSH)-secreting pituitary adenoma presenting with hypokalemic periodic paralysis is extraordinarily rare and may be misdiagnosed. We describe a 44-year-old man who suffered from acute muscle weakness and inability to ambulate upon awakening in the morning. Physical examination showed hypertension, tachycardia, and symmetrical flaccid paralysis of all extremities. The major biochemical abnormality was hypokalemia (K+, 2.0 mmol/L) with low urine K+ excretion. A thyroid function study revealed elevated thyroid hormone levels and inappropriately high TSH concentrations (2.10 microU/mL). Brain magnetic resonance imaging delineated a pituitary tumor with suprasellar extension. After trans-sphenoidal removal of tumor, he became clinically and biochemically euthyroid without any further attack of paralysis. Pathological findings confirmed a TSH-secreting adenoma with exclusive TSH immunostaining. TSH-secreting pituitary adenoma must be kept in the differential diagnosis in any thyrotoxic periodic paralysis patients with detectable TSH levels to avoid delaying diagnosis and management.