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Thyrotoxic Periodic Paralysis — ESENeph MCQ

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HardElectrolyte DisordersThyrotoxic Periodic ParalysisESENeph

A 35-year-old man presents with hypokalaemic periodic paralysis (K+ 2.0 mmol/L, muscle weakness). He has thyrotoxicosis (suppressed TSH, elevated free T4). Urine potassium is low. What is the mechanism?

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Correct answer: D — Thyrotoxicosis activates Na+/K+-ATPase causing intracellular potassium shift (redistributive hypokalaemia); urine K is low because renal excretion is normal

Thyrotoxic periodic paralysis is caused by excessive thyroid hormone-mediated activation of Na+/K+-ATPase, driving potassium intracellularly. This is redistributive (shift) hypokalaemia, not renal wasting – hence urine potassium is appropriately low. It is more common in Asian men. Acute treatment is cautious potassium replacement (risk of rebound hyperkalaemia as the shift reverses). Definitive treatment is correction of thyrotoxicosis. Beta-blockers (Propranolol) can also help acutely by reducing Na+/K+-ATPase activity.

Reference: Lin and Bhatt 2019 – Thyrotoxic Periodic Paralysis Review