Periodic paralysis

Periodic paralysis is a group of rare neuromuscular disorders characterized by episodes of muscle weakness or paralysis that occur intermittently, with normal or near-normal muscle function between attacks. The condition primarily affects skeletal muscles and is caused by dysfunction of ion channels (channelopathies) in muscle cell membranes, most commonly involving sodium, calcium, or potassium channels. The major subtypes include hypokalemic periodic paralysis (HypoPP), hyperkalemic periodic paralysis (HyperPP), and Andersen-Tawil syndrome. Attacks can be triggered by factors such as carbohydrate-rich meals, rest after exercise, stress, cold exposure, or changes in serum potassium levels. During episodes, patients experience flaccid weakness that can range from mild focal weakness to severe generalized paralysis, typically sparing respiratory and cardiac muscles. Episodes may last from minutes to hours or even days depending on the subtype. Between attacks, patients may initially have normal strength, but over time many individuals develop a progressive fixed myopathy (permanent muscle weakness) that can significantly impact mobility and quality of life. In Andersen-Tawil syndrome, cardiac arrhythmias and distinctive facial and skeletal features may also be present. Diagnosis is based on clinical history, electromyography (including the long exercise test), genetic testing, and provocative testing in specialized centers. Treatment focuses on preventing attacks and managing acute episodes. Carbonic anhydrase inhibitors such as acetazolamide and dichlorphenamide are commonly used as preventive therapies. Potassium supplementation is used in hypokalemic forms, while dietary modifications and avoidance of known triggers are important management strategies. Dichlorphenamide (Keveyis) is the only FDA-approved medication specifically indicated for primary periodic paralysis. Long-term monitoring for progressive myopathy and, in Andersen-Tawil syndrome, cardiac surveillance are essential components of care.

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