Grand Rounds Contributor: Case Report/Focused Review
Hypokalemic Thyrotoxic Periodic Paralysis With Thyrotoxic Psychosis and Hypercapnic Respiratory Failure

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Abstract

Thyrotoxic periodic paralysis is a rare and potentially lethal neuromuscular disease that manifests as recurrent episodic muscle weakness associated with hypokalemia and thyrotoxicosis. Paralysis can rarely involve respiratory muscles leading to acute respiratory failure. The disease primarily affects people of Asian descent, but it is being increasingly reported in other ethnic groups. We review the literature and report a case of hypokalemic thyrotoxic periodic paralysis manifesting as thyroid storm with episodic acute respiratory failure requiring recurrent intubation and eventually requiring thyroidectomy for resolution of symptoms.

Section snippets

CASE REPORT

A 27-year-old Korean man with no medical or surgical history was brought to the hospital with vague complains of anorexia, insomnia, muteness, and disinterest. All of his symptoms had begun since his wife left him and went back to Korea. According to the family, during the past 3 to 4 days, the patient had been behaving unlike his usual self and had been in a labile mood. In the emergency room, he was agitated, screaming loudly and incoherently. He was pulling out intravenous (IV) lines and was

DISCUSSION

Hyperthyroidism refers to a disorder of accelerated synthesis and secretion of thyroid hormones from the thyroid gland. Thyrotoxicosis is a hypermetabolic clinical syndrome resulting from any cause of excessive serum thyroid hormone concentration. The thyroid storm is an extreme manifestation of thyrotoxicosis involving a severe systemic dysfunction of the thermoregulatory, central nervous, cardiovascular, and gastrointestinal systems. TPP is a rare thyroid disorder associated with

TYPES

TPP is a well-established phenomenon.2 In general, hypokalemic paralysis can be divided into 2 main groups: hypokalemic periodic paralysis (HPP) and the non-HPP. The HPP occurs due to an acute and massive shift of potassium into the cells, whereas the non-HPP occurs due to a large total body deficit.3 According to cause, the HPP can be further grouped into the TPP and the familial periodic paralysis. Similarly, the non-HPP can be grouped into Bartter syndrome/Gitelman syndrome, renal tubular

EPIDEMIOLOGY

TPP is most widely known and studied in the Asian population, including Chinese, Japanese, Vietnamese, Filipino, and Koreans. Its incidence is 10-fold higher in this population compared with the whites.4., 7. Sporadic cases have been reported in the non-Asian populations, including the whites, Afro-Americans, and Hispanic.8

Despite the higher incidence of thyroid disease in women, this entity is far more common in men with a preponderance ratio of 17:1 to 70:1.7., 9., 10. Approximately 80% of

CLINICAL PRESENTATION

TPP is a rare neurologic manifestation of thyrotoxicosis. The neurologic manifestations of thyrotoxicosis are limited and rare. In many cases, they present in conjunction with the systemic features of the disease but may be the presenting symptoms in some patients.

The neurologic manifestations of thyrotoxicosis are as follows:

  • 1.

    Cognitive impairment and seizures: cognitive impairment with behavioral and personality changes are common in hyperthyroidism. It is usually subacute but may progress to

DIAGNOSIS

The diagnosis of TPP must be suspected on clinical grounds. A recurrent clinical pattern of flaccid paralysis with evidence of hyperthyroidism supports the diagnosis. The presence of hypokalemia and absence of an acid-base disorder also strengthen the diagnostic likelihood.6

PATHOPHYSIOLOGY

The exact pathophysiology of TPP is unknown; however, various theories have been suggested. The hypokalemia seen in TPP is the result of the increased Na K ATPase activity, which results in massive shift of potassium from the extracellular to the intracellular compartment and causes hypokalemia without causing urinary losses.34., 35., 36. Both catecholamines and insulin are well-known hormones involved in increased intracellular shift of potassium and phosphate.37., 38. Hyperinsulinemia, which

Correction of K+

Prompt correction of potassium with immediate IV/oral supplementation can prevent serious cardiopulmonary complications. Patient may require anywhere between 40 and 200 mEq of KCl.37., 50. Lu et al50 reported that 40% of patients who received >40% of IV KCl at a rate of 10 mEq/hr developed rebound hyperkalemia to levels >5.5 mEq/L. It is thus recommended that KCl be replaced at a slow rate unless cardiopulmonary complications warrant otherwise.

Nonselective beta blockers have also been shown to

DIFFERENTIAL DIAGNOSES

All periodic paralyses are characterized by episodic weakness. Motor strength remains normal between attacks. The following diagnoses must be considered and ruled out before committing to the diagnosis of thyrotoxic HPP.

SUMMARY

TPP is a disorder characterized by concurrent thyrotoxicosis, hypokalemia, and progressive symmetrical weakness leading to paralysis. It is rare in non-Asians and therefore a high clinical suspicion is required for early diagnosis and prompt initiation of management, which can prevent potentially serious and life-threatening consequences. Although the exact mechanism of TPP is unknown, it is attributed to the enhanced activity of the Na-K ATPase leading to increased influx of potassium and

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