PC3094: Thyrotoxic Periodic Paralysis in a Caucasian Adolescent Male

Introduction: We present an interesting case of thyrotoxic periodic paralysis in a Caucasian adolescent male.

Case Description: History: A 19-year-old Caucasian male presented to the pediatric emergency department with acute onset of bilateral lower extremity weakness. Symptoms began one day prior with difficulty moving his legs or standing after waking from sleep. No recent fevers, respiratory symptoms, numbness, paresthesia or myalgia but had emesis and transient dyspnea before coming to the emergency department.

Physical examination: On arrival he was found to be hypertensive and tachycardic. Physical examination revealed 1/5 strength in bilateral lower extremities but full strength in upper extremities. His sensation was intact throughout. The remainder of the exam was within normal limits.

Diagnostic work-up: Labs showed hypokalemia of 1.9 mmol/L, mild metabolic acidosis of 18 mmol/L and mildly elevated creatinine kinase of 247 U/L. Cardiac and infectious labs were otherwise negative. His electrocardiogram showed prolonged PR intervals with flattening of the T waves and U waves most notable in the lateral precordial leads and V3. He received parenteral potassium chloride and anti-emetics. Neurology was consulted and deferred imaging given his hypokalemia. He was admitted to the PICU for cardiac monitoring. His neurologic symptoms resolved after potassium administration and intravenous fluid therapy. Thyroid function tests revealed hyperthyroidism (FT4 3.87 ng/dl and TSH less than 0.03 IU/ml). Endocrinology recommended obtaining Thyroid Stimulating Immunoglobulins and receptor antibodies, which were later found to be elevated at 14.40 IU/L. Thyroid ultrasound during admission showed an enlarged heterogeneous thyroid gland without any nodules.

Final diagnosis: The patient was diagnosed with thyrotoxic periodic paralysis due to Graves’ Disease. Metoprolol was initially recommended for acute thyrotoxicosis management. He was later switched to propranolol and started on daily methimazole prior to discharge. At the time of discharge, he had full strength in all four extremities. He is awaiting treatment for radioiodine ablation.

Discussion: Thyrotoxic periodic paralysis is characterized by hypokalemia, acute onset of lower extremity weakness and hyperthyroidism. It is mostly found in adult Asian males and is often overlooked in Western countries and the pediatric population. In the past two decades, less than 20 cases in adolescents have been reported. The pathophysiology is unclear; however the theory is hyperthyroidism increases tissue responsiveness to beta-adrenergic stimulation which increases sodium-potassium ATPase activity on the skeletal muscle membrane, leading to an intracellular potassium shift resulting in hypokalemia, muscle weakness and potential cardiac arrhythmias. Acute treatment involves potassium replacement with cardiac monitoring given the risks of hyperkalemia. A beta-blocker may reverse adrenergic hyperstimulation but treating hyperthyroidism is the most definitive management.

Conclusion: Our case emphasizes the importance of maintaining normokalemia in a patient presenting with acute paralysis and to have low threshold for checking thyroid function. Prompt recognition and management can prevent morbidity and mortality.