Hyperkalemic Periodic Paralysis

Abstract

Hyperkalemic periodic paralysis (HyperPP) is characterized by episodic attacks of muscle weakness or paralysis associated with an increased potassium concentration in blood (sometimes very mild and fugitive), which begin in childhood and may vary in frequency, duration (few minutes to hours), and severity (focal paresis to total paralysis). The attacks usually involve the limb muscles, spare the facial and respiratory muscles, and are triggered by rest after exercise, fasting, cold exposure, ingestion of potassium-rich food, stress, infection, steroids, anesthesia, and pregnancy. Maintaining exercise alleviates symptoms. Some patients present clinical myotonia that frequently involves facial muscles (lid-lag sign, eye closure myotonia), while most patients present electrical myotonia (EMG may record myotonic discharges and myopathic features).

About 80 % of patients with hyperPP present one missense mutation (p.T704M, p.M1592V) in the SCN4A gene, encoding the alpha subunit of the skeletal muscle voltage-gated sodium channel (Table 42.1), leading to defective inactivation of the channel. Muscle biopsy may show fiber atrophy with vacuoles.