Periodic Paralyses

Periodic paralyses are rare disorders of voluntary muscles. They are characterized by episodes or attacks of muscle weakness. However, between these attacks, affected muscles usually work normally.

The two most common types are hypokalemic (low potassium) and hyperkalemic (high potassium) periodic paralyses. Both forms may be inherited, or occur without a family history. If inherited, they often occur in an autosomal dominant fashion, meaning that children of affected parents have a 50 percent chance of getting the disease.

Hypokalemic periodic paralysis
Often referred to as familial paralysis, hypokalemic periodic paralysis is characterized by a decrease in potassium levels in the blood.

Attacks of hypokalemic periodic paralysis are usually triggered by exercising too strenuously, eating high carbohydrate or high salt meals, or taking drugs such as insulin. Attacks generally begin in adolescence and may last from four to 24 hours. The frequency of attacks vary, but are usually more severe than those occurring in hyperkalemic periodic paralysis.

During an attack of muscle weakness, otherwise normal potassium levels in the bloodstream are low. The muscle weakness is a result of less potassium flowing from the bloodstream and into the muscle cells. The most common muscle groups affected are the arms and legs; however, the disorder may also affect the swallowing and respiratory muscles, which can be fatal in severe cases.

Between attacks, patients often experience normal muscle strength, but after repeated attacks (over many years), persistent muscle weakness may occur.

Hyperkalemic periodic paralysis
Unlike hypokalemic attacks, hyperkalemic periodic paralysis is not associated with low potassium levels in the bloodstream. In fact, during an attack, the potassium levels may be normal or even high. Instead, the muscle weakness is thought to be the result of an abnormality in the muscle cell walls and the bodyís inability to control electrolyte levels.

Attacks typical of hyperkalemic periodic paralysis are frequent and brief, usually lasting one to two hours. They often occur upon awakening and can be triggered by strenuous exercise or stress. Attacks generally begin in very young patients, often before age one. Muscle weakness generally affects the arms and legs, although it may eventually affect the heart muscle, causing abnormal heart rhythms. Like hypokalemic paralysis, strength is normal between attacks, but eventually persistent weakness may occur.

Patients with this type of periodic paralysis often experience difficulty relaxing their muscles, a condition called myotonia. For instance, they may not be able to release their grip after shaking somebodyís hand. This muscle stiffness or myotonia persists between attacks.

The doctor will obtain a detailed medical history and review a patientís family medical history. The medical history is often the biggest clue to the diagnosis. A thorough physical examination is then performed.

Between attacks, the only abnormality on physical examination may be clinical myotonia (in hyperkalemic periodic paralysis), or poor muscle relaxation. Other tests include:

Since attacks usually donít occur during an office visit, the doctor may give the patient a prescription to have blood potassium checked during an attack. This can be performed in a variety of emergency rooms and laboratories. Occasionally, attacks can be brought on in the office by changing the potassium level with medications such as insulin. However, this practice should only be performed under careful monitoring of experienced neurologists.

Treatment and management
There is no cure for periodic paralyses. As a result, the treatment focuses on preventing further attacks and relieving symptoms like myotonia. Attacks of periodic paralysis are rarely life threatening, and some attacks can be so brief that they do not require treatment. However, over time these attacks can eventually lead to permanent muscle weakness, so treatment should be sought as soon as possible.

For patients with hypokalemic periodic paralysis, administering potassium may stop an attack. Still, taking regular doses of potassium will not prevent future attacks. Potassium is generally taken by mouth, but in a case of severe muscle weakness, the patient would need to receive it intravenously in a hospital. Another management tool for hypokalemic attacks is to eat a low-carbohydrate and low-salt diet. Medications such as acetazolamide have also been effective in preventing some attacks and have been effective in patients with hyperkalemic periodic paralysis.

For patients with hyperkalemic periodic paralysis, a high-carbohydrate diet may be recommended. When a patient is experiencing an attack, glucose or other forms of carbohydrates may be given in an effort to reduce the severity of the attack. In severe cases, glucose may need to be given intravenously.

While the prognosis for patients with periodic paralyses varies, in general most patients respond well to treatment and can lead active, productive lives. For more information on periodic paralyses, contact the following organizations:

Muscular Dystrophy Association
3300 East Sunrise Drive
Tucson, AZ 85718-3208
(800) 344-4863

National Organization for Rare Disorders (NORD)
55 Kenosia Avenue
P.O. Box 1968
Danbury, CT 06813-1968
(203) 744-0100
(800) 999-6673 (voicemail only)
TDD Number: (203) 797-9590

© Copyright 1995-2005 The Cleveland Clinic Foundation. All rights reserved


This information is provided by the Cleveland Clinic and is not intended to replace the medical advice of your doctor or health care provider. Please consult your health care provider for advice about a specific medical condition. For additional health information, please contact the Center for Consumer Health Information at the Cleveland Clinic (216) 444-3771 or toll-free (800) 223-2273 extension 43771. If you prefer, you may visit or This document was last reviewed on: 1/9/2002