Periodic Paralysis
Periodic paralysis is an autosomal dominant inherited disorder that causes sudden attacks of weakness and paralysis; there are several variants.
During an attack of periodic paralysis, muscles do not respond to normal nerve impulses or even to artificial stimulation with an electronic instrument. The person remains completely awake and alert. The precise form that the disorder takes varies in different families. In some families, the paralysis is related to high levels of potassium in the blood (hyperkalemia); in others, the paralysis is related to low levels of potassium in the blood (hypokalemia) or, rarely, to normal levels.
Symptoms and Diagnosis
In the hyperkalemic form of the disorder, attacks often begin by age 10. The attacks last 15 minutes to 1 hour. In the hypokalemic form, attacks generally first appear before age 16 but may appear during the 20s and always by age 30. The attacks last longer (occasionally for 2 to 3 days) and are more severe. Fasting, strenuous work, and exposure to cold may precipitate attacks in people who have the hyperkalemic form. Some people with the hypokalemic form are prone to attacks of paralysis after eating meals rich in carbohydrates (sometimes hours or even the day after), but exercise also precipitates attacks. Eating carbohydrates and exercising vigorously drive sugar into cells; potassium moves with the sugar and the result is lowered potassium levels in the blood. On awakening the day after engaging in vigorous exercise, a person with either the hyperkalemic form or the hypokalemic form may feel some weakness or even paralysis in certain muscle groups or in the arms and legs. The weakness generally lasts 1 or 2 days.
A doctor's best clue to the diagnosis is a person's description of a typical attack. If possible, the doctor draws blood while an attack is in progress to check the level of potassium. Doctors usually perform additional tests to be sure abnormal potassium levels in the blood are not from other causes.
Prevention and Treatment
Acetazolamide, a drug that alters the blood's acidity, may prevent attacks in all types of periodic paralysis. People with the hypokalemic form can take potassium chloride in an unsweetened solution while the attack is in progress. Usually symptoms improve considerably within an hour. People with the hypokalemic form should also avoid meals rich in carbohydrates and strenuous exercise. People with the hyperkalemic form can prevent attacks by eating frequent meals rich in carbohydrates and low in potassium.
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