Definition

Periodic paralysis is a rare condition that is usually inherited. It causes occasional episodes of severe muscle weakness. The 2 most common types of periodic paralysis are hypokalemic and hyperkalemic.

Causes

Periodic paralysis is a condition that is present from birth. Periodic paralysis is caused by abnormalities of the electrolyte channels on muscles.

Familial periodic paralysis is inherited, but may occur without a known family history. With the inherited form of the disorder, only 1 affected parent is needed to transmit the gene to the baby. Rarely, the condition occurs as a result of a noninherited genetic defect.

Risk Factors

Factors that increase your chance of developing periodic paralysis include:

• Family history of periodic paralysis
• Thyroid disorder—high thyroid hormone levels, particularly in Asian males

Symptoms

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

Episodes of severe weakness in the arms and legs are the major symptom. Typically, these episodes occur during sleep, early morning, or 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—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, 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 is 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.

Diagnosis

Because this primarily is an inherited condition, the most important part of diagnosis is obtaining a family history. You will be asked about your symptoms and your medical history. A physical exam will be done.

Your doctor may want 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
• Thyroid tests
• Electrocardiogram (ECG, EKG)
• Electromyography (EMG)

Your muscle tissue may need to be tested. This can be done with a biopsy.

Treatment

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

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.

For the hypokalemic type, attacks may be reduced by:

• Avoiding corticosteroids and glucose infusions
• Following a diet low in carbohydrates and sodium and rich in potassium

For the hyperkalemic type, attacks may be reduced by:

• Avoiding high potassium foods, fasting, and drugs known to increase potassium levels
• Engaging in regular, mild exercise

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

Muscular Dystrophy Canada http://muscle.ca

Jurkat-Ratt K, Lehmann-Horn F. Paroxysmal muscle weakness-the periodic paralyses. J Neurol. 2006;253:1391-1398.

Jurkatt-Rott K, Lerche H, Weber Y, Lehmann-Horn F. Hereditary channelopathies in neurology. Adv Exp Med Biol. 2010;686:305-334.

Miller TM. Correlating phenotype and genotype in the periodic paralyses. Neurology. 2004;63:1647-1655

NINDS familial periodic paralyses information page. National Institute of Neurological Disorders and Stroke website. Available at:
http://www.ninds.nih.gov/disorders/periodic_paralysis/periodic_paralysis.htm
Updated March 12, 2012. Accessed June 22, 2015.

Patient page: attacks of immobility caused by diet or exercise? The mystery of periodic paralyses. Neurology. 2004;63:E17-E18.