Thyrotoxic Periodic Paralysis in Young Caucasian Male

Abstract

Background: Thyrotoxic periodic paralysis (TPP) can be a medical emergency as delay in diagnosis can lead to life-threatening arrhythmia. Periodic paralysis is more prevalent in the Asian population. We report a case of thyrotoxic periodic paralysis in a young Caucasian male. Case: A 24-year-old male with a past history of Graves’ disease, hypertension, and asthma was brought to the hospital due to leg weakness and fall. He was initially diagnosed with Graves’ disease 2 years ago. The patient could not take methimazole or metoprolol due to the affordability issue for the last 18 months. On presentation, he fell on the floor while attempting to stand up from the couch. He could not stand up or pick his cell phone. He remained on the floor for 2-3 hrs. A review of the system was positive for palpitation and fatigue and negative for diarrhea, weight loss, anxiety, sleep problem, and dry eyes. On arrival, he had a pulse of 100/min, BP of 157/85 mmHg with rest of vitals signs normal. Motor strength on bilateral lower extremities were 2/5. Upper extremity strength was normal. No thyromegaly or thyroid bruit was noted in the exam. The rest of the physical exam was normal. Labs showed Potassium 1.9 with a normal reference range (RR) of 3.5 - 5.1 mmol/l. His TSH was < 0.01 (RR 0.35 - 5.00 MCU/ML), Free T4 was 5.0 (RR 0.6- 1.6 NG/DL), Total T3 was 425 (RR 87 - 180 NG/DL) and CK was 70 (RR 35- 232 U/L). EKG showed sinus rhythm at 90 bpm with no PR, T/ST, or QT abnormalities. He was given IV potassium and was also started on methimazole 10mg TID and metoprolol. His weakness and tachycardia were improved the next day. We discussed with him the options of medical management vs. surgery. He underwent a total thyroidectomy. Biopsy showed nodular hyperplasia consistent with graves’ disease. Discussion: Thyrotoxic periodic paralysis (TPP) is characterized by hypokalemia and episode of acute muscle weakness in lower extremities in the setting of hyperthyroidism. The pathophysiology of TPP remains uncertain. Hyperthyroidism is a hyperadrenergic state in which beta-2-adrenergic stimulation in muscle cells directly induces cellular K+ uptake by increasing cAMP, leading to activation of Na/K ATPase. The increase in the influx of intracellular K+ leads to hypokalemia and skeletal muscle weakness. Some studies show pathophysiology can be different in Caucasians compared to the Asian population that there could be abnormalities in Na and K channels other than Na/K ATPase. Potassium replacement should be done with caution as hypokalemia is due to intracellular shift and rebound hyperkalemia is common during the management. Beta-blocker may reverse adrenergic overstimulation of Na/K ATPase. It can help rapidly improve paralytic symptoms.