Thyrotoxic Periodic Paralysis

Thyrotoxic periodic paralysis is hypokalemic weakness similar to HPP. Patients are usually male (95%), Asian (90%), and between 20 to 39 years old (80%). Weakness usually precedes other manifestations of thyrotoxicosis. The exact mechanism causing paralysis is unknown.

Causes

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.

Symptoms

• Similar to HPP. It presents as episodic weakness progressing over hours, typically after awakening from sleep. It affects the extremities (legs > arms) and the trunk.
• Sensation and sensorium are intact.
• Tremulousness (from hyperthyroidism) may be present.

Signs

• Similar to HPP. Reflexes are absent or diminished. Bulbar muscles and diaphragm are spared. The patient may also show signs of thyroid hormone excess: tachycardia, goiter, exophthalmos, or lid lag.

Treatment

The best treatment is rapid reduction in thyroid hormone levels. Potassium should also be given during the attack. It is preferred that potassium be given by mouth, but if weakness is severe, intravenous potassium may be necessary.

A diet that is low in carbohydrates and salt may be recommended to prevent attacks. In addition, medications called beta-blockers may reduce the number and severity of attacks while hyperthyroidism is brought under control.