This is a rare condition that occurs only in people with high thyroid hormone levels (thyrotoxicosis). It is most commonly seen in Asian men.
There is a similar disorder, called hypokalemic periodic paralysis (familial periodic paralysis). It is an inherited condition and is not related to high thyroid levels.
Risk factors include a family history of periodic paralysis and hyperthyroidism.
Symptoms involve attacks of muscle weakness or paralysis that alternate with periods of normal muscle function. Attacks usually begin after symptoms of hyperthyroidism have developed.
How often attacks occur varies from daily to yearly. Episodes of muscle weakness may last for a few hours or several days.
The weakness or paralysis:
- Comes and goes
- Can last for up to several days
- Is more common in the legs than the arms
- Is most common in the shoulders and hips
- Is triggered by heavy, high-carbohydrate, high-salt meals
- Is triggered by rest after exercise
Other symptoms may include any of the following:
- Difficulty breathing (rare)
- Speech difficulty (rare)
- Swallowing difficulty (rare)
- Vision changes (rare)
People are alert during attacks. Normal strength returns between attacks. Muscle weakness may develop over time with repeated attacks.
Symptoms of hyperthyroidism include:
Exams and Tests
The health care provider may suspect thyrotoxic periodic paralysis based on:
- Abnormal thyroid hormone levels
- A family history of the disorder
- Low potassium levels during attacks
- Symptoms that come and go in episodes
Diagnosis involves ruling out disorders associated with low potassium.
The health care provider may try to trigger an attack by giving you insulin and sugar (glucose, which reduces potassium levels) or thyroid hormone.
During an attack, there may be the following signs:
- Decreased or no reflexes
- Heart arrhythmias
- Low potassium in the bloodstream (serum potassium levels are normal between attacks)
- Weakness, especially in the muscles of the arms and legs and occasionally in the muscles of the eyes. The muscles involved in breathing and swallowing can very rarely be affected, and this can be fatal. Muscle strength is normal between attacks at first. However, repeated attacks may eventually cause worsening and persistent muscle weakness.
Between attacks, the examination is normal. Or, there may be signs of hyperthyroidism, such as an enlarged thyroid.
The following tests are used to diagnose hyperthyroidism:
- High thyroid hormone levels (T3 or T4)
- Low serum TSH (thyroid stimulating hormone) levels
- Thyroid uptake and scan
Other test results:
- Abnormal electrocardiogram (ECG) during attacks
- Abnormal electromyogram (EMG) during attacks
- Low serum potassium during attacks, but normal between attacks
A muscle biopsy may sometimes be taken.
The best treatment is to quickly reduce thyroid hormone levels. Potassium should also be given during the attack, usually by mouth. If weakness is severe, you may need to get potassium through a vein (intravenously). (You should only get intravenous potassium if your kidney function is normal and you are monitored in the hospital.)
Weakness that involves the muscles used for breathing or swallowing is an emergency. Patients must be taken to a hospital. Dangerous heart arrhythmias may also occur during attacks.
Your health care provider may recommend eating a diet that is low in carbohydrates and salt to prevent attacks. Medications called beta-blockers may reduce the number and severity of attacks while your hyperthyroidism is brought under control.
Acetazolamide is effective at preventing attacks in people with familial periodic paralysis. It is usually not effective for thyrotoxic periodic paralysis.
Chronic attacks over time can lead to muscle weakness. This weakness can continue even between attacks if the thyrotoxicosis is not treated.
Thyrotoxic periodic paralysis responds well to medical treatment. Treating hyperthyroidism will prevent attacks and may even reverse muscle weakness.
- Difficulty breathing, speaking, or swallowing during attacks (rare)
- Heart arrhythmias during attacks
- Muscle weakness that gets worse over time
When to Contact a Medical Professional
Go to the emergency room or call the local emergency number (such as 911) if you have periods of muscle weakness. This is especially important if you have a family history of periodic paralysis or thyroid disorders.
Emergency symptoms include:
- Difficulty breathing, speaking, or swallowing
- Falls due to muscle weakness
Genetic counseling may be advised. Treating the thyroid disorder prevents attacks of weakness.
Periodic paralysis - thyrotoxic
Mandel SJ, Larsen PR, Davies F. Thyrotoxicosis. In: Melmed S. Polonsky KS, Larsen PR, Kronenberg HM, eds. Williams Textbook of Endocrinology. 12th ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 12.
Klubo-Gwiezdzinka J, Wartofsky L. Thyroid emergencies. Med Clin N Am. 2012;96:385-403.
Pothiwala P, Levine SN. Analytic review: thyrotoxic periodic paralysis: a review. J Intensive Care Med
Update Date 5/10/2014
Updated by: Brent Wisse, MD, Associate Professor of Medicine, Division of Metabolism, Endocrinology & Nutrition, University of Washington School of Medicine, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.