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Familial Periodic Paralysis


Michael Rubin

, MDCM, New York Presbyterian Hospital-Cornell Medical Center

Reviewed/Revised Jan 2024

Familial periodic paralysis is a rare inherited disorder that causes sudden attacks of weakness and paralysis. There are 4 different forms, which involve abnormalities in how electrolytes Overview of Electrolytes More than half of a person's body weight is water. Doctors think about water in the body as being restricted to various spaces, called fluid compartments. The three main compartments are Fluid... read more , such as sodium and potassium, are moved in and out of cells.

  • Muscles do not respond normally to stimulation if the blood potassium level is too low or high.

  • Weakness is intermittent, affecting mainly the limbs, and is often brought on by exercising or eating too many or too few carbohydrates.

  • The diagnosis is based on the symptoms, a check of the potassium level in the blood, and the results of an exercise test.

  • Avoiding triggers that cause attacks and taking certain medications can prevent attacks effectively.

Attacks of familial periodic paralysis occur in response to the amount of potassium in a person's blood. Potassium is an electrolyte Overview of Electrolytes More than half of a person's body weight is water. Doctors think about water in the body as being restricted to various spaces, called fluid compartments. The three main compartments are Fluid... read more and is necessary for the normal functioning of cells, nerves, and muscles (see Overview of Potassium's Role in the Body Overview of Potassium's Role in the Body Potassium is one of the body's electrolytes, which are minerals that carry an electric charge when dissolved in body fluids such as blood. (See also Overview of Electrolytes.) Most of the body’s... read more ). During an attack of familial periodic paralysis, muscles do not respond to normal nerve impulses or even to artificial stimulation with an electronic instrument.

The precise form that the disorder takes varies among different families. There are 4 forms:

  • Hypokalemic

  • Hyperkalemic

  • Thyrotoxic

  • Andersen-Tawil syndrome

In Andersen-Tawil syndrome, potassium levels can be high, low, or normal.

Symptoms of Familial Periodic Paralysis

During an attack of weakness, the person remains completely awake and alert. Muscles in the eye and face are not affected. Weakness may affect only certain muscles or all 4 limbs.

Hypokalemic periodic paralysis

In this form, attacks generally first appear before age 16 but may appear during the 20s and always by age 30. The attacks last up to 24 hours.

Often, the person awakens the day after vigorous exercise with an attack of weakness. The weakness may be mild and limited to certain muscle groups or may affect all 4 limbs. However, eating meals rich in carbohydrates (sometimes hours or even the day before), emotional or physical stress, alcohol ingestion, and exposure to cold can also cause attacks. Eating carbohydrates and exercising vigorously drive sugar into cells. Potassium moves with the sugar, and the result is lowered potassium levels in the blood and urine.

Hyperkalemic periodic paralysis

In this form, attacks often begin by age 10. The attacks last 15 minutes to 1 hour. Weakness tends to be less severe than in the hypokalemic form. Fasting, rest shortly after exercise, or exercise after meals may trigger attacks.

Myotonia (very stiff muscles caused by a delayed ability to relax the muscles after contracting them) is common. Myotonia of the eyelids may be the only symptom.

Thyrotoxic periodic paralysis

In this form, attacks of weakness last hours to days and are usually triggered by exercise, stress, or eating foods rich in carbohydrates, similar to the hypokalemic form.

People have symptoms of hyperthyroidism, such as anxiety, tremors, palpitations, and heat intolerance.

Andersen-Tawil syndrome

In this form, attacks of weakness usually begin before age 20 and are triggered by rest after exercise. Episodes may last for days and occur monthly.

Diagnosis of Familial Periodic Paralysis

  • Description of an attack

  • Level of potassium in the blood during an attack

  • Exercise test

  • Genetic testing

A doctor’s best clue to the diagnosis of familial periodic paralysis is a person’s description of a typical attack. If possible, the doctor draws blood while an attack is in progress to check the level of potassium. If the level of potassium is abnormal, doctors usually do additional tests to be sure the abnormal level is not the result of other causes.

In the past, doctors based the diagnosis on provocative testing. In provocative testing, doctors give a person medications by vein (intravenously) that increase or decrease the level of potassium in the blood to see whether they provoke or cause an attack. However, provocative testing may cause serious side effects such as paralysis of the breathing muscles or an abnormal heart rhythm. Thus, provocative testing has been replaced by a safer exercise test.

In the exercise test, doctors have the person vigorously exercise a single muscle for 2 to 5 minutes to see if that makes the muscle weak. Doctors record electrical activity from the muscle before and after exercise to see if it was affected.

Treatment and Prevention

  • Depends on the form

Hypokalemic periodic paralysis

People with this form can take potassium chloride in an unsweetened solution or have it injected into a vein while an attack is in progress. Usually symptoms improve considerably within an hour.

People with the hypokalemic form should also avoid meals rich in carbohydrates and salt, avoid alcohol after periods of rest, and avoid strenuous exercise. Acetazolamide, a medication that alters the blood’s acidity, may help prevent attacks.

Hyperkalemic periodic paralysis

People with this form can stop a mild attack by doing light exercise and eating a carbohydrate-rich meal. If an attack is persistent, medications (such as a thiazide diuretic or inhaled albuterol) can help lower the potassium level. If an attack is severe, doctors give calcium or insulin and glucose by vein.

People can prevent attacks by eating frequent meals rich in carbohydrates and low in potassium and by avoiding fasting, strenuous activity after meals, and exposure to cold.

Thyrotoxic periodic paralysis

People with this form are given potassium chloride (as in the hypokalemic form), and doctors closely monitor levels of potassium in the blood during severe attacks.

To prevent attacks, doctors give people medications to keep their thyroid gland functioning properly and beta-blockers (such as propranolol).

Andersen-Tawil syndrome

More Information

The following English-language resource may be useful. Please note that THE MANUAL is not responsible for the content of this resource.

Drugs Mentioned In This Article

Generic Name Select Brand Names
Cena K , ED-K+10, Epiklor, K Plus, K Plus Care, K-10 , K-8, Kaon-CL, Kay Ciel , K-Dur, K-Lor, Klor-Con, Klor-Con M10, Klor-Con M15, Klor-Con M20, Klotrix, K-Lyte CL, K-Sol , K-Tab, Micro-K, Micro-K Extencaps, POKONZA, PROAMP, Rum-K, Slow-K, Tri-K
Diamox, Diamox Sequels
Accuneb, ProAir digihaler, Proair HFA, ProAir RespiClick, Proventil, Proventil HFA, Proventil Repetabs, Respirol , Ventolin, Ventolin HFA, Ventolin Syrup, Volmax, VoSpire ER
Afrezza, Exubera
HEMANGEOL, Inderal, Inderal LA, Inderal XL, InnoPran XL
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