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What are the periodic paralysis disorders?
Periodic paralysis disorders are muscle channelopathies that consist of hyperkalemic (potassium sensitive) PP, hypokalemic PP, and Andersen–Tawil syndrome (ATS).
All are inherited in an autosomal dominant fashion. All present with recurrent attacks of weakness, ranging from mild and focal to severe generalized weakness.
Over time, patients might develop fixed weakness. ATS patients have dysmorphic features (e.g., hypertelorism, mandibular hypoplasia, clinodactyly, syndactyly, scoliosis, short stature, high-arched palate) and cardiac arrhythmias (commonly long QT syndrome).
During attacks, serum CK is usually elevated with serum potassium levels being variable (high, low, or normal).
Between attacks, EMG may show myotonia in hyperkalemic PP patients, while muscles are electrically silent in all types during an episode of weakness.
Differentiating Periodic Paralysis Disorders
Hyper PP | Hypo PP | ATS | |
---|---|---|---|
Gene | SCN4A | CACNA1S > SCN4A | KCNJ2 |
Triggers of weakness | Rest after exercise | Stress | Rest after exercise |
Fasting | EtOH | Carbohydrates | |
High K + food | Carb-rich food | Potassium | |
Rest after exercise | |||
Duration of weakness | Minutes to hours | Hours to days | Hours to days |
Associated features | Myotonia | Dysmorphic | |
Cardiac arrhythmias | |||
Number of episodes per month | 10-20 | <10 | Variable |
hypoPP = hypokalemic periodic paralysis, hyperPP = hyperkalemic periodic paralysis, ATS = Andersen Tawil Syndrome