Periodic paralysis is a rare inherited condition that causes occasional episodes of severe muscle weakness. The two most common types of periodic paralysis are hypokalemic and hyperkalemic.

Causes

Periodic paralysis is a congenital condition—that is, it is present from birth. Familial periodic paralysis is inherited but may occur without a known family history.

The inherited form of the disorder is autosomal dominant, which means that only one affected parent is needed to transmit the gene to the baby. When one parent is affected, the child has a 50% chance of getting the disease. Rarely, the condition occurs as a result of a non-inherited genetic defect.

Risk Factors

A risk factor is something that increases your chances of getting a disease or condition. Those at increased risk of having periodic paralysis are:

• Children and adolescents

• Asian

• Male

• Those with a family history of periodic paralysis

• Those with thyroid disorders (particularly in Asian males)

Symptoms

While muscle strength returns to normal between attacks, repeated bouts of weakness may lead to chronic muscle weakness later in life. The person remains alert and aware during attacks, and there is no accompanying loss of sensation.

Episodic bouts of severe weakness in the arms and legs are the most prominent symptom. Typically these bouts occur during sleep, especially after strenuous activity. Cold, stress, and alcohol may also produce attacks. Other, less common, symptoms may include:

• Weakness in the eyelids and face muscles

• Muscle pain

• Irregular heartbeats

• Difficulty breathing or swallowing (if this occurs, proceed immediately to the nearest emergency room)

Some features are specific to the type of periodic paralysis.

• Hypokalemic:

• • Potassium levels are low during attacks

• • Frequency of attacks varies from daily to yearly

• • Attacks usually last between 4-24 hours, but can last for several days

• • Attacks usually begin in adolescence, but they can occur before age 10

• Hyperkalemic:

• • Potassium levels are high during attacks

• • Attacks are usually shorter (lasting 1-2 hours), more frequent , and less severe than the hypokalemic form; breathing and swallowing difficulties are extremely rare

• • Between attacks, patients often experience muscle spasms or difficulty relaxing their muscles, a condition known as myotonia

• • Attacks usually begin in early childhood

Diagnosis

Because this primarily is an inherited condition, the most important aspect of diagnosis is obtaining a family history. In addition to asking about symptoms and your medical history, your doctor will perform a physical exam.

Attacks don’t usually occur during an office visit, so your doctor may prescribe several blood tests to check potassium levels during an attack. These tests can be performed in an emergency room or laboratory.

Your doctor may wish to bring on an attack during an office visit. This should only be done under careful monitoring by an experienced neurologist.

Giving oral glucose or glucose and subcutaneous insulin may trigger a hypokalemic attack, whereas giving potassium may trigger a hyperkalemic attack. If an attack is triggered, several tests may be administered. They include:

• Electrocardiogram (ECG) to test for abnormal activity of the heart

• Electromyography (EMC) to test the functioning of nerves and muscles

A muscle biopsy, in which a small piece of muscle tissue is removed and then sent to the lab for analysis, may be performed if the diagnosis is in question.

Treatment

Since there is no cure for periodic paralysis, lifelong treatment of periodic paralysis is usually required. Treatment focuses on preventing attacks and relieving symptoms.

Lifestyle Changes

There are a few behaviors you can adopt to reduce the frequency and severity of attacks:

• Hypokalemic:

• • Eat a low carbohydrate, low sodium diet

• • Avoid strenuous exercise

• Hyperkalemic:

• • Eat a low potassium diet

• • Stay warm

• • Avoid fasting, alcohol, and unaccustomed heavy exercise

Medications

• Both hypokalemic and hyperkalemic:

• • Acetozolamide (Diamox): may prevent an attack by reducing the flow of potassium from the bloodstream into the cells of the body

• Hypokalemic:

• • Potassium (pill or liquid form) may stop an attack; intravenous potassium may be prescribed for severe weakness

• • Avoiding certain commonly prescribed medications may help reduce the onset of attacks

• • Treat thyroid disorder if present

• Hyperkalemic:

• • Thiazide diuretics, or ‘water pills,’ may be prescribed to prevent an attack

• • Glucose, glucose and insulin, or calcium carbonate may be prescribed to slow or stop an attack

Prevention

Familial periodic paralysis cannot be prevented. Because it can be inherited, genetic counseling may be advised for couples at risk of passing on the disorder.

RESOURCES:

Muscular Dystrophy Association
http://www.mdausa.org

National Organization for Rare Disorders (NORD)
http://www.rarediseases.org

Periodic Paralysis Resource Center
http://www.periodicparalysis.org

CANADIAN RESOURCES:

Muscular Dystrophy Canada
http://www.mdac.ca

References:

Miller TM. Correlating phenotype and genotype in the periodic paralyses. Neurology. 2004;63(9):1647-55

National Institute of Neurological Disorders and Stroke website. Available at: http://www.ninds.nih.gov. Accessed August 2005.

Patient page: attacks of immobility caused by diet or exercise? The mystery of periodic paralyses. Neurology. 2004;63(9):E17-8.

Periodic Paralysis Association website. Available at: http://www.periodicparaysis.org. Accessed August 2005.