Skin Deep: A Rare Case of Thyrotoxic Periodic Paralysis in an African American Patient

Background: Thyrotoxic Periodic Paralysis (PP) is a rare form of hypokalemic PP that occurs in association with hyperthyroidism, especially Grave’s disease. This disease is frequently seen in males and is particularly prevalent among Asians with an incidence rate of 2%. In non-Asian populations, the incidence among those with hyperthyroidism is even lower at 0.1 - 0.2% and therefore significantly rare in African populations. Inability to recognize this emergency in the non-Asian population can therefore result in potentially fatal outcomes. Case Presentation: A 27 year old African American male with a history of Grave’s disease presented to the emergency department (ED) with the inability to move his muscles. Patient was initially diagnosed with Grave’s disease in 2017 when he was found to have suppressed TSH with elevated TSI and started on methimazole 40mg daily. The patient ran out of methimazole about 2 weeks prior to presentation and woke up on the day of admission with extreme muscle weakness. At the outside hospital, he was found to have potassium of 1.5mEq/L,TSH of < 0.1uL/ml and Free T4 of 3.4 ng/dL. He was given 1000 mg Propylthiouracil, stress dose hydrocortisone, propranolol and potassium replacement and then transferred to our ED for Endocrine evaluation. On assessment, he complained of nausea, vomiting, full body muscle weakness, tingling in his extremities and irritability. He denied any recent illnesses. On physical exam, Temperature 97.4 F, Respiration 18, Pulse 84, BP 157/72, O2 saturation 99%. His thyroid gland was enlarged however non-tender and without bruit. He had normal respiratory and cardiac exam. He was lying flat in bed and unable to raise his limbs against gravity and also unable to hold up his limbs when raised. He lacked his patellar and ankle jerk reflexes bilaterally. He was otherwise alert and oriented x 3. On labs, TSH was 0.004 uL/ml, Total T3 was 294 ng/dL, Free T4 of 3.01 ng/dL, Potassium was 2.1 mEq/L. His potassium was cautiously replaced and improved to 4.7 mEq/L later in the day, at which time, the patient was able move and sit up in bed. He was restarted on Methimazole 40mg daily for his thyroid disease and arranged for outpatient follow up. Discussion: Thyrotoxic PP is seen in a male-to-female ratio ranging from 17:1 to 70:1 and occurs at an average age of 20-40 years. Thyrotoxic PP is especially rare in the non-Asian population at an incidence rate of 0.1 - 0.2%. Nevertheless, in setting of ever-growing diversity due to immigration and inter-race relationships, it is difficult to predict one’s genetics based on the color of their skin. It is possible that our African American patient may have an Asian ancestor unbeknownst to him. Therefore, we must keep a broad differential regardless of one’s race so as to not miss timely diagnosis of medical emergencies which can result in reduced muscle strength, flaccid paralysis, respiratory failure, cardiac arrhythmias and eventual death.