What is Thyrotoxic Hypokalemic Periodic Paralysis?
Thyrotoxic Hyperkalemic Periodic Paralysis (TPP) is an uncommon disorder with three characteristics which occur at the same time:
- too much 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, but only occasionally in those of European descent.
The thyroid gland is part of the endocrine system. It is located in the neck and produces several hormones that help control growth, digestion, and metabolism. A complex set of mechanisms control the rate of thyroid gland activity. Too much thyroid hormone (called hyperthyroidism or thyrotoxicosis) is due to an overactive thyroid gland. Hyperthyroidism is not a specific disease, but a symptom of an underlying condition or disease. The causes of hyperthyroidism include Graves’ disease; tumours 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.
What tests are used to diagnose TPP?
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.
No one else in my family has this disease. How did I get it?
It’s been clear for many years that most types of periodic paralysis are inherited, but until recently the relationship between inheritance and TPP was unclear. It seemed obvious that there was some genetic factor at work, or TPP wouldn’t occur more often in men of Asian ancestry, but no genetic mutation could be identified. In 2010 a team of researchers discovered a group of mutations which increase a person’s chance of developing TPP. Since then over 20 genetic mutations associated with Thyrotoxic HypoKPP have been identified. While these still do not explain all cases they help to establish a genetic basis for the disorder. But even when a TPP mutation is inherited a person will not develop symptoms unless their thyroid becomes overactive. This means generations might pass in a family between two affected individuals.
What triggers attacks of TPP?
The same factors which trigger attacks of Hypokalemic Periodic Paralysis will trigger attacks of TPP if thyroid levels are too high. Meals high in starchy and sweet foods may trigger an attack. Taking thyroid hormones may trigger an attack. Sleep or resting after vigorous exercise may trigger an attack. For a more complete discussion on triggers see the section on Hypokalemic Periodic Paralysis.
How do I avoid having attacks?
Your physician will treat the underlying thyroid disorder, which will eventually cure your TPP. In the meantime you should determine what triggers your attacks and avoid those triggers. Medication is usually necessary until the thyroid problem is brought under control.
What medications are prescribed for TPP?
Beta-blockers like propranolol are used to treat TPP, along with a potassium supplement. But the overactive thyroid must be treated. Once the underlying thyroid problem is corrected with medication, radiation or surgery the symptoms of TPP usually disappear.