Manifestations of Hypokalemic Paralysis

Thyrotoxic periodic paralysis (TPP) is a rare emergency condition that occurs in individuals with hyperthyroidism. The typical clinical presentation involves the sudden onset of limb weakness or paralysis, often during the night or upon waking in the morning. It is often associated with habits of consuming a high-carbohydrate diet, alcohol abuse, or vigorous exercise.

According to literature and case reviews, this condition is more commonly seen in people of Asians. Historically, the incidence of TPP in Asian patients with hyperthyroidism is approximately 2%, while in the United States, it ranges from 0.1% to 0.2%. The age group most affected is typically between 20 and 40 years old. Generally, hyperthyroidism is more prevalent in females, but TPP tends to be more common in males, with a male-to-female ratio of approximately 17:1.

Symptoms

The symptoms of TPP include generalized or localized muscle weakness, with weakness predominantly affecting proximal muscles (such as the upper arms and thighs) more severely than distal muscles. It usually affects the lower limbs more than the upper limbs, and the duration of muscle weakness can range from hours to several days. During episodes, deep tendon reflexes are reduced or absent, and these episodes can recur over the course of several days.

Patients with TPP typically experience these symptoms only when they have hyperthyroidism. If thyroid function is within the normal range, the condition is less likely to occur. However, when in a state of hyperthyroidism, the condition is easily triggered by factors such as consuming a high-sugar diet, alcohol consumption, or strenuous exercise and should be avoided whenever possible.

Etiology

The hypokalemia (low blood potassium) caused by TPP is due to the temporary movement of potassium ions into cells. Elevated levels of thyroid hormone increase the activity of the sodium-potassium pump (Na+/K+-ATPase), leading to an increased chance of potassium ions entering muscle cells. Hypokalemia may result from the shift of potassium ions into cells, there is no significant loss of potassium ions, and the total potassium content in the body is not deficient.

The primary underlying cause of TPP is hyperthyroidism. Therefore, in its treatment, anti-thyroid medications (such as methimazole or propylthiouracil) and propranolol are administered to restore thyroid function to normal. If medication management is inadequate, surgical intervention or radioactive iodine-131 therapy can also be considered to improve limb weakness symptoms and reduce the occurrence of arrhythmias. Since hypokalemia is due to the temporary movement of potassium ions into cells and not an actual deficiency in total body potassium ions, potassium supplementation should be administered in appropriate amounts and under the careful evaluation of a physician.