Hypokalaemic periodic paralysis (HypoKPP)
A rare, usually autosomal‑dominant channelopathy causing episodic flaccid weakness due to acute hypokalaemia. Presentations range from mild proximal weakness to profound paralysis with respiratory compromise or cardiac arrhythmia.
In the emergency setting, recognise HypoKPP as a reversible metabolic cause of acute flaccid weakness, treat life‑threatening hypokalaemia and its complications promptly, and arrange specialist follow‑up for definitive diagnosis and prevention.
Pathophysiology and genetics
Mutations in skeletal muscle ion‑channel genes alter membrane excitability and potassium handling, producing attacks when potassium shifts intracellularly. The common genes are:
- CACNA1S - skeletal muscle L‑type calcium channel (most frequent).
- SCN4A - skeletal muscle voltage‑gated sodium channel.
These mutations cause aberrant ionic currents and impaired action potential propagation. Triggers that drive potassium into cells (insulin surge, β‑adrenergic stimulation, post‑exercise recovery) precipitate marked serum hypokalaemia and weakness. Genetic testing can confirm the diagnosis but is not always positive; a characteristic history and electrophysiology (long‑exercise EMG) support diagnosis.
Typical clinical features
- Sudden, often bilateral flaccid weakness, classically proximal
distal in limbs.