Thyrotoxic Hypokalemic Periodic Paralysis FAQ
What is Thyrotoxic Hypokalemic Periodic Paralysis?
Thyrotoxic Hyperkalemic Periodic Paralysis (TPP) is an uncommon disorder with three characteristic symptoms which all occur at the same time:
- elevated thyroid hormone
- low levels of potassium in the blood (hypokalemia)
- muscle weakness or paralysis
TPP occurs most often in males of Asian descent, including Japanese, Chinese, Vietnamese, Korean and Filipinos It also occurs more frequently in those of Native American and Latin American descent.
About 0.1% to 0.2% of Caucasians in North American with hyperthyroid develop TPP as compared with 1.8% to 8.8% in Asia. An increased incidence is also seen in Hispanic and Native American men. Although the association between an overactive thyroid and periodic paralysis has been well known since the early 1930s, TPP is still often overlooked by physicians in the United States because of a lack of familiarity with the disorder. Physicians in Asian countries usually recognize TPP much more readily.
The thyroid gland is part of the endocrine system. It is located in the neck and produces a number of different hormones that regulate growth, digestion, and metabolism. A complex set of mechanisms control the rate of thyroid gland activity. Hyperthyroidism or thyrotoxicosis results from excess quantities of thyroid hormone within the body.
Hyperthyroidism is not a specific disease, but more a symptom of some underlying condition or disease. The causes of hyperthyroidism include Graves' disease; tumors of the thyroid or other endocrine glands; inflammation or infection of the thyroid; taking too much thyroid hormone; and taking too much iodine. Graves' disease accounts for 85% of all cases of hyperthyroidism.
No one in my family has this disease. How did I get it?
In most cases periodic paralysis is inherited, but until recently the relationship between inheritance and development of symptoms in TPP was unclear. It seemed obvious that there was some genetic factor at work, or TPP wouldn't be more prominent in men of Asian ancestry, but the genetic factor eluded science. In November of 2002 a team of researchers in Brazil announced discovery of a potassium-channel mutation which results in the symptoms of Thyrotoxic Hypokalemic Periodic Paralysis. While there may be more than one mutation which causes TPP, this is a real breakthrough and helps to establish a genetic basis for the disorder.
But even when TPP mutation is inherited a person will not develop symptoms unless their thyroid becomes overactive. This means generations might pass between symptomatic individuals.
What triggers attacks of TPP?
Generally things which trigger attacks of HypoKPP will trigger attacks of TPP. High carbohydrate or high salt meals may trigger an attack. Taking thyroid hormones may trigger an attack. Attacks most commonly occur after sleep or rest and are rare during exercise, but rest after exercise may trigger an attack. For a more complete discussion on triggers see the section on Hypokalemic Periodic Paralysis
How can I determine what causes my attacks?
See How to Determine Episode Triggers
How do I avoid having attacks?
Your physician will treat the underlying disorder, which will eventually cure your TPP. In the meantime, to control your episodes you should determine your triggers and learn to avoid them. Some people can avoid episodes of paralysis by avoiding their triggers. For others medication is necessary until their other problems are brought under control.
What tests are used to diagnose TPP?
To check for Hyperthyroidism the doctor will do blood tests to check the levels of various thyroid hormones including; TSH levels, T3, T3 resin uptake and T4. During an attack of weakness the doctor will do a blood test to check the level of potassium. In TPP, the level of potassium is low during attacks but normal between attacks.
Can I have genetic test for TPP?
There is no DNA test available for TPP.
What medications are prescribed for TPP?
Beta-blockers like propranolol are used to treat TPP initially, along with potassium. Further measures include life-style modification with a low carbohydrate diet, avoidance of strenuous exercise, and use of a Medic Alert bracelet. But these measures are temporary. The overactive thyroid must be treated. Once the underlying thyroid problem is corrected the symptoms usually disappear. The thyroid activity will be treated appropriately, depending on the problem. When the thyroid secretions normalize the periodic paralysis almost always disappears.
We hope this has answered your basic questions about Thyrotoxic Periodic Paralysis. For medical references see our Physician's Sheet: Thyrotoxic PP.