Thyrotoxicosis Presenting as Hypokalemic, Periodic Paralysis in a Previously Healthy 14-year-old Male

Abstract

Introduction: Hypokalemic periodic paralysis (HPP) is an unusual manifestation of hyperthyroidism. It is the most common cause of acquired HPP, and more common in males of Asian descent. For patients with HPP, it is also important to identify the underlying etiology to prevent recurring episodes of potentially life-threatening paralysis. Case Presentation: A previously healthy 14-year-old male was brought to the Emergency Department with acute, motor paralysis of both lower extremities. On physical examination, he was able to move all extremities but had a persistent, generalized weakness. The deep tendon reflexes were normal, and cranial nerves and sensation were intact. Vitals were within reference range except for elevated respiratory rate. In the Emergency Department, his potassium was noted to be very low at 1.5 mmol/L (ref: 3.5-5.0 mmol/L). BUN, creatinine, bilirubin, alkaline phosphatase, sodium, and chloride were all within normal range. A thyroid panel revealed a TSH of Discussion: HPP requires prompt treatment, since deaths from respiratory failure and arrhythmia have been reported1. The differential diagnoses of HPP have been discussed in other publications. The link between HPP and thyrotoxicosis is reported to be an increased β2-adrenergic stimulation resulting from the elevated levels of thyroid hormone. This leads to cellular potassium uptake in muscle, disrupting the polarity of the membrane and causing problems with proper muscle cell stimulation. Once the thyroid hormone levels are normalized, the hypokalemia should cease and episodes of paralysis averted. The condition, when present, often manifests prior to other more common symptoms such of thyrotoxicosis. Conclusions: Our case illustrates an unusual, but potentially life-threatening manifestation of thyrotoxicosis. Proper diagnosis is critical to successful long-term management. It is important to measure thyroid function studies (thyroid stimulating hormone and free T4) in all patients who present with unexplained periodic paralysis to avoid misdiagnosis.