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Hypokalemic Periodic Paralysis.

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GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2014.
2002 Apr 30 [updated 2009 Apr 28].

Excerpt

DISEASE CHARACTERISTICS:

Hypokalemic periodic paralysis (HOKPP) is characterized by a paralytic form and a myopathic form. The paralytic form is characterized by attacks of reversible flaccid paralysis with concomitant hypokalemia, usually leading to paraparesis or tetraparesis but sparing the respiratory muscles and heart. Acute paralytic crises usually last at least several hours and sometimes days. Some individuals have only one episode in a lifetime; more commonly, crises occur repeatedly: daily, weekly, monthly, or less often. The major triggering factors are carbohydrate-rich meals and rest after exercise; rarely, cold-induced hypokalemic paralysis has been reported. The interval between crises may vary and may be prolonged by preventive treatment with potassium salts or acetazolamide. The age of onset of the first attack ranges from one to 20 years; the frequency of attacks is highest between ages 15 and 35 and then decreases with age. The myopathic form develops in approximately 25% of affected individuals and results in a progressive fixed muscle weakness that begins at variable ages as exercise intolerance predominantly in the lower limbs. It occurs independent of paralytic symptoms and may be the sole manifestation of HOKPP. Individuals with HOKPP are at increased risk for pre- or post-anesthetic weakness and have a risk for malignant hyperthermia that is increased but not as high as that for individuals with true autosomal dominant malignant hyperthermia susceptibility (MHS).

DIAGNOSIS/TESTING:

The diagnosis of HOKPP is based on a history of episodes of flaccid paralysis; low serum concentration of potassium (<0.9 to 3.0 mmol/L) during attacks, but not between attacks; the absence of myotonia clinically and on electromyography (EMG) (with the exception of one family with heat-induced myotonia and cold-induced HOKPP); the absence of hyperthyroidism; the absence of dysmorphic traits and cardiac arrhythmias; and a family history consistent with autosomal dominant inheritance. Of all individuals meeting diagnostic criteria for HOKPP, approximately 55%-70% have mutations in CACNA1S and approximately 8%-10% in SCN4A.

MANAGEMENT:

Treatment of manifestations: Paralytic crises are treated with oral or IV potassium to normalize the serum concentration of potassium and to shorten the paralytic episode. ECG and blood potassium concentration must be monitored during treatment. Prevention of primary manifestations: Diet low in sodium and carbohydrate and rich in potassium; oral intake of potassium salts; acetazolamide in some individuals. Prevention of secondary complications: Attention to risk factors for malignant hyperthermia. Surveillance: Varies by symptoms and response to preventive treatment; monitoring focuses on frequency, intensity, and duration of weakness attacks. Neurologic examination should focus on muscle strength in the legs to detect permanent weakness associated with myopathy. Agents/circumstances to avoid: Triggers of paralytic attacks including unusually strenuous effort, excess of carbohydrate-rich meals, sweets, alcohol, and glucose infusion. Corticosteroids should be used with care. Evaluation of relatives at risk: When the family-specific mutation is known, molecular genetic testing of at-risk, asymptomatic family members can identify those at risk for unexpected acute paralysis and/or malignant hyperthermia.

GENETIC COUNSELING:

HOKPP is inherited in an autosomal dominant manner. Most individuals diagnosed with HOKPP have an affected parent. The proportion of cases caused by a de novo gene mutation is unknown. Offspring of a proband have a 50% risk of inheriting the mutation. Penetrance is about 90% in males and may be as low as 50% in females depending on the causative mutation. Prenatal testing is possible if the disease-causing mutation has been identified in the family; however, requests for prenatal testing for conditions such as HOKPP that do not affect intellect and have some treatment available are not common.

Copyright © 1993-2014, University of Washington, Seattle. All rights reserved.

PMID:
20301512
[PubMed]
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