Thyrotoxic periodic paralysis is a condition in which there are episodes of severe muscle weakness. It occurs in people who have high levels of thyroid hormone in their blood (hyperthyroidism, thyrotoxicosis).
This is a rare condition that occurs only in people with high thyroid hormone levels (thyrotoxicosis). Asian and Hispanic men are affected more often. Not everyone who develops high thyroid hormone levels will be at risk of periodic paralysis.
There is a similar disorder, called hypokalemic, or familial, periodic paralysis. It is an inherited condition and not related to high thyroid levels, but has the same symptoms.
Risk factors include a family history of periodic paralysis and hyperthyroidism.
Symptoms involve attacks of muscle weakness or paralysis. The attacks alternate with periods of normal muscle function. Attacks often begin after symptoms of hyperthyroidism have developed.
The frequency of attacks varies from daily to yearly. Episodes of muscle weakness may last for a few hours or several days.
The weakness or paralysis:
Other rare symptoms may include any of the following:
People are alert during attacks and can answer questions. Normal strength returns between attacks. Muscle weakness may develop over time with repeated attacks.
Symptoms of hyperthyroidism include:
The health care provider may suspect thyrotoxic periodic paralysis based on:
Diagnosis involves ruling out disorders associated with low potassium.
The provider may try to trigger an attack by giving you insulin and sugar (glucose, which reduces potassium level) or thyroid hormone.
The following signs may be seen during the attack:
Between attacks, the examination is normal. Or, there may be signs of hyperthyroidism, such as an enlarged thyroid changes in the eyes, tremor, hair and nail changes.
The following tests are used to diagnose hyperthyroidism:
Other test results:
A muscle biopsy may sometimes be taken.
Potassium should also be given during the attack, usually by mouth. If weakness is severe, you may need to get potassium through a vein (IV). Note: You should only get IV 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. People must be taken to a hospital. Serious irregularity of heartbeat may also occur during attacks.
Your provider may recommend a diet that is low in carbohydrates and salt to prevent attacks. Medicines 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.
If an attack isn't treated and the breathing muscles are affected, death can occur.
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 treatment. Treating hyperthyroidism will prevent attacks and may even reverse muscle weakness.
Untreated thyrotoxic periodic paralysis can lead to:
Call the local emergency number (such as 911) or go to the emergency room 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:
Genetic counseling may be advised. Treating the thyroid disorder prevents attacks of weakness.
Reviewed 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, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.