Thyrotoxic Periodic Paralysis: A Rare Presentation of Graves’ Disease

Abstract

Abstract Background: Thyrotoxic periodic paralysis (TPP) is a rare but serious thyroid emergency characterized by hypokalemia, acute onset flaccid paralysis & thyrotoxicosis. Typically, seen in an Asian male with untreated hyperthyroidism symptoms, who awakens at night or in the early morning with flaccid ascending paralysis. This is precipitated by exercise, alcohol or carbohydrate rich meal. TPP is widely reported & studied in Asian population. Its prevalence is about 2 % in Asian hyperthyroid patients. However, incidence is 0.1-0.2% in non-Asian hyperthyroid patients. Clinical Case: 33-year-old Caucasian male with celiac disease and no thyroid disease sought emergency care for complaints of sudden onset severe weakness in all extremities. He reported 20-pound unintentional weight loss, intermittent palpitations and low-grade fever. He noticed leg cramps with numbness and unable to move his extremities. At initial evaluation, he had acute flaccid paralysis and tachycardia. Initial laboratory studies showed potassium at 1.9 mmol/l, Magnesium at 1.8, suppressed TSH <0.005 uIU/ml with elevations in free T4 at 2.43 ng/dl and total T3 at 1.9 ng/ml. CT and MRI head were normal. Patient’s aldosterone level was normal. The patient’s paralysis and hypokalemia resolved after potassium replacement. Thyroid stimulating immunoglobulin was elevated and increased vascularity suggestive of Grave’s disease noted on thyroid Ultrasound. Methimazole and propranolol were initiated. His neurological workup was negative. After resolution of paralysis and hypokalemia he was discharged home. Since our patient presented with severe hypokalemia, flaccid paralysis and hyperthyroidism, that resolved promptly with potassium replacement, hence likely diagnosis of thyrotoxic periodic paralysis. Discussion: Thyrotoxic periodic paralysis is potentially reversible and mostly seen with Graves’ disease among Asian population. Early diagnosis & treatment prevents life threatening complications. Differential diagnosis of TPP includes familial periodic paralysis, Guillain-Barre Syndrome & acute intermittent porphyria. Diagnosis is based on family history, characteristic presentation, hyperthyroidism with low serum potassium level. Possible mechanism is increased sodium-potassium ATPase activity in the skeletal muscle membrane leading to intracellular shift of potassium causing hypokalemia and muscle inexcitability. Treatment includes potassium replacement, nonselective beta-blocker and definitive treatment of hyperthyroidism, to prevent further episodes.