Images of Hyperthyroidism: Thyrotoxic Periodic Paralysis

A 17-year-old adolescent experienced an episode of generalized paralysis ofacute onset after physical exertion and consumption of a high-carbohydratemeal. Despite a good appetite, the patient had lost between 2 and 3 lb duringthe past month. He complained of heat intolerance and palpitations and reportedlosing his temper easily.Tremor in both hands, lid lag, and slight exophthalmos were noted; pulserate was 88 beats per minute. The thyroid gland was 2 1/2 times the normal size.Potassium level was 1.8 mmol/L (normal, 3.5 to 5 mmol/L); bicarbonate, 19mmol/L (normal, 21 to 31 mmol/L); free thyroxine, 49.4 pmol/L (normal,8 to 22 pmol/L); and thyroid-stimulating hormone, less than 0.05 mU/L (normal,0.2 to 6 mU/L).Thyrotoxic periodic paralysis was diagnosed. Periodic paralysis is a raremyopathic disorder that is characterized by episodic attacks of symmetric flaccidparalysis that are typically precipitated by exposure to cold, high-carbohydratemeals, rest after exercise, alcohol, infection, trauma, menstruation, oremotional excitement. The serum potassium level may be normal, low, or highduring paralytic attacks.Although periodic paralysis is usually familial, sporadic cases may be associatedwith hyperthyroidism. It has been suggested that excessive amountsof thyroid hormone increase the permeability of the muscle membranes toelectrolytes, which results in an influx of potassium into the cells.This patient was given methimazole, 25 mg/d. His thyroid function testresults and serum potassium level normalized; the periodic paralysis did notrecur.