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.

Periodic paralysis is a congenital condition, meaning it is present from birth. Familial periodic paralysis is inherited, but may occur without a known family history. Periodic paralysis is caused by abnormalities of the electrolyte channels on muscles.

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 noninherited genetic defect.

These factors increase your chance of developing periodic paralysis. Tell your doctor if you have any of these risk factors:

• Family history of periodic paralysis
• Thyroid disorder (particularly in Asian males)

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 ( arrhythmias )
• Difficulty breathing or swallowing—This requires emergency care.

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 or normal 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

Persons with some types of periodic paralysis are at risk for a condition known as malignant hyperthermia. This can occur during the use of general anesthesia . Anyone with a family history of periodic paralysis needs to notify the anesthesiologist of this history prior to any surgery.

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.

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. If an attack is triggered, several tests may be done, including:

• Blood tests to look for the gene mutation or to look for antibodies that may cause these types of symptoms.
• Electrocardiogram (ECG, EKG)—a test that records the heart's activity by measuring electrical currents through the heart muscle
• Electromyography (EMG)—to test the functioning of nerves and muscles

If the diagnosis is in question, your doctor may do a muscle biopsy .

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

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 heavy exercise.

• Both hypokalemic and hyperkalemic:
  • Acetazolamide (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.
  • If you have a thyroid condition, be sure to get treatment for it.
• 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.