Thyrotoxic Periodic Paralysis

Thyrotoxic periodic paralysis (TPP) is a rare complication of thyrotoxicosis characterized by acute, reversible episodes of muscle weakness and hypokalemia. It is often precipitated by heavy exercise or high-carbohydrate meals and is most commonly described in Asian men. Although the pathogenesis remains unclear, the recurrent paralytic muscle weakness is caused by hypokalemia resulting from a shift of potassium (K+) into the intracellular space without a total K+ deficit. The clinical features of TPP and the factors precipitating the acute paralysis episodes are similar to those of familial periodic paralysis associated with hypokalemia which is an autosomal dominant channelopathy more common in Caucasians. Although rare, early treatment of TPP is necessary to avoid reversible but potentially life-threatening complications, such as cardiac arrhythmias and respiratory failure. Symptoms and signs of thyrotoxicosis may be subtle in TPP so the diagnosis requires an awareness of precipitants and clinical features with recognition of biochemical and electrocardiography abnormalities. Treatment doses of potassium chloride required to recover from paralysis need to be minimized to avoid rebound hyperkalemia. Non-selective β-blockers can prevent paradoxical hypokalemia associated with hyperadrenergic activity. Treatment of the underlying cause of thyrotoxicosis (usually Graves' disease) should completely abolish further attacks of TPP.