Thyrotoxic periodic paralysis
Key points
- Thyrotoxic periodic paralysis a syndrome characterized by intermittent episodes of muscle weakness that occurs in people with high levels of thyroid hormone (Thyrotoxicosis, Hyperthyroidism).
- Thyrotoxic periodic paralysis is a rare condition that occurs only in people with Thyrotoxicosis (high thyroid hormone levels).
- The health care provider may suspect thyrotoxic periodic paralysis based on a family history of the disorder, the episodic nature of symptoms, low potassium levels during attacks, abnormal thyroid hormone levels, and elimination of other disorders associated with low potassium as the cause of symptoms.
- The best treatment is rapid reduction in thyroid hormone levels.
Alternative names
Periodic paralysis - thyrotoxic
Definition
Thyrotoxic periodic paralysis a syndrome characterized by intermittent episodes of muscle weakness that occurs in people with high levels of thyroid hormone (Thyrotoxicosis, Hyperthyroidism).
Causes, incidence, and risk factors
Thyrotoxic periodic paralysis is a rare condition that occurs only in people with Thyrotoxicosis (high thyroid hormone levels). It is seen most commonly in Asian men. There is a similar disorder, hypokalemic periodic paralysis (familial periodic paralysis), that is an inherited condition and is not associated with high thyroid levels.
Thyrotoxic periodic paralysis involves attacks of muscle weakness or paralysis alternating with periods of normal muscle function. Attacks usually 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 may persist for several days.
During an attack, there is a low level of potassium in the bloodstream (serum). Serum potassium levels are normal between attacks. There is no decrease in total body potassium, however.
Normally, potassium flows from the bloodstream into muscle cells.When levels of potassium are low (hypokalemia), there may not be enough for proper muscle function. Insulin levels may affect the disorder because insulin increases the flow of potassium into cells.
Weakness most commonly affects the muscles of the arms and legs. It may occasionally affect the muscles of the eyes. The muscles involved in breathing and swallowing can sometimes be affected and this can be fatal.
Heart arrhythmias can also occur during attacks because of the drop in potassium levels. Although muscle strength is initially normal between attacks, repeated attacks may eventually cause progressive and persistent muscle weakness.
Risk factors include a family history of periodic paralysis and Hyperthyroidism. Attacks may be triggered by eating high-carbohydrate or high-salt meals. Rest after vigorous exercise can also trigger an attack.
Symptoms
- weakness/paralysis
o most common in shoulders and hips
o more common in legs than arms
o intermittent occurrences
o triggered by rest after exerciseo triggered by heavy, high-carbohydrate, high-salt mealso lasting for up to several days
Written and revised by
David Cohen, M.D.
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