Primary Periodic Paralyses

Episodes when muscles won't move

The muscle disorders known as primary periodic paralyses (PP) are characterized by periods of loss of function of muscles. During an episode of paralysis, an individual is unable to move parts (sometimes all) of his or her body. The paralysis results from changes in the flow of sodium, calcium, or potassium within muscle cells. The paralysis does not usually affect the facial or respiratory muscles.

The periodic paralyses are a group of disorders that are usually inherited but may occur in an individual as a new genetic mutation. The types include:

• hyperkalemic periodic paralysis
• hypokalemic periodic paralysis
• paramyotonia congenita
• Andersen-Tawil syndrome
• potassium-associated myotonia

It is not known how frequently all the different types occur throughout the world.

Symptoms
Individuals with a periodic paralysis disorder experience episodes in which they are unable to move parts of their bodies. These episodes can occur days, weeks, months, or years apart. Recovery occurs after a short period of time, especially with medical treatment to correct the underlying imbalance that brought on the paralysis. The episodes often first occur in childhood or adolescence. Some individuals may have difficulty relaxing their muscles (myotonia) between episodes of paralysis.

• Hyperkalemic PP – Episodes of paralysis are brought on by high potassium intake, exposure to cold, rest after exercise, or emotional stress. Individuals with this type may have myotonia between episodes.
• Hypokalemic PP – Episodes of paralysis are brought on by high-carbohydrate or high-sodium foods (which cause a decrease in blood potassium), by exposure to cold, or rest after exercise.
• Paramyotonia congenita – Individuals with this disorder have myotonia, which may be made worse by activity. The muscles of the face are often affected. Episodes of weakness may be brought on by exposure to cold.
• Andersen-Tawil syndrome – Individuals with this disorder have specific facial features (such as low-set ears and small lower jaw), small stature, and irregular heartbeats (cardiac arrhythmias) in addition to the episodes of periodic paralysis.
• Potassium-associated myotonia – Individuals with this disorder have myotonia. Episodes of weakness are uncommon but may be brought on by exposure to cold or rest after exercise.

After many episodes of paralysis, persistent muscle weakness may develop.

Diagnosis
Any type of periodic paralysis may be difficult to diagnose since most doctors have no experience with these disorders. Because of this some individuals with PP may be misdiagnosed with another neurological or muscular disorder, or told they have a psychiatric, not physical, problem.

Some of the tests which may help diagnose a periodic paralysis disorder are tests to check the levels of potassium, sodium, chloride, and phosphorus in the blood; nerve conduction studies in muscles; exercise tests, and tests which are designed to bring on an episode of paralysis (called provocative testing). A muscle sample (biopsy) can be taken and examined under the microscope for changes typical of periodic paralysis.

Treatment of paralysis episodes and long-term

• Hyperkalemic PP – Episodes are usually mild and do not usually require treatment. Muscle weakness improves with high-carbohydrate foods. For severe episodes, treatment focuses on reducing the potassium level in the blood. Medications used to reduce the frequency of episodes include acetazolamide (Diamox) and/or diuretics such as chlorothiazide (Diuril) and chlorthalidone (Hygroton). Mexiletine (Mexitil) has proven effective for myotonia. Individuals with hyperkalemic PP should avoid eating too much potassium at one time. Foods high in potassium include bananas, orange juice, honeydew, cantaloupe, dried fruits, some nuts, and sunflower seeds.
• Hypokalemic PP – During a paralysis episode, oral potassium is given until the weakness improves. Medications used to reduce the frequency of episodes include acetazolamide (Diamox), dichlorphenamide (Daranide), and/or diuretics that conserve potassium, such as triamterene (Dyrenium) and spironolactone (Aldactone). Individuals with hypokalemic PP should avoid high-carbohydrate or high-sodium meals, which cause a decrease in blood potassium. Many prepared, frozen, and canned foods are high in sodium and should not be eaten.
• Paramyotonia congenita – Treatment is focused on reducing myotonia. Mexiletine has proven effective for this.
• Potassium-associated myotonia – Treatment is focused on reducing myotonia. Mexiletine or diuretics such as chlorothiazide and chlorthalidone may be effective.
• Andersen-Tawil syndrome – Treatment is based on the individual’s needs and symptoms.

Sources:
- Sripathi, N. (2006). Periodic paralyses. eMedicine, accessed at http://www.emedicine.com/neuro/topic308.htm
- Wahl, M. (1998). Not crazy or lazy: Periodic paralysis brings frustration, misunderstanding, but can be managed. Muscular Dystrophy Association, Quest, Vol. 5.