SUN-547 Primary Autoimmune Hypothyroidism Presenting with Sleep Apnea and Recurrent Episodes of Rhabdomyolysis in a Pediatric Patient: A Case Report

Background: Hypothyroid myopathy has different presentations including rhabdomyolysis, Hoffman’s syndrome, acute compartment syndrome and Kocher-Debre-Semelaigne syndrome, with most cases being reported in adults. Rarity of this condition in pediatric population, leads to delay in diagnosis of underlying hypothyroidism in children with myopathy. Pathophysiology is not fully understood but is known to occur due to deposition of glycosaminoglycans, poor contractility of actin-myosin units, low myosin ATPase activity, and low ATP turnover in skeletal muscle [1].Treatment with thyroxine replacement results in resolution of myopathy. Clinical Case: A 13-year-old female presented to the emergency department with 4 weeks of intermittent abdominal pain. She reported history of strenuous exercise but denied any exposure to medications. Workup revealed elevated creatine kinase of 2411 units/L ( 21-232 units/L) and creatinine 1.2 mg/dL (0.3-1.0 mg/dL). Creatinine kinase level came down to 1891 units/L after two days of IV hydration and she was discharged with diagnosis of viral or exercise induced rhabdomyolysis. Four weeks later patient returned due to worsening edema and six pound weight gain. Workup revealed elevated creatine kinase 7936 units/L. Thyroid function studies obtained showed an elevated TSH 318 microIU/mL (0.40-5.34 microIU/mL), low Free T4 level 0.13 ng/dL (0.65-2.30 ng/dL), low total T4 0.5 mcg/dL (5.6-14.4 mcg/dL), positive titers of thyroid peroxidase antibody 642 IU/ml (0.0-9.0 IU/mL) and thyroglobulin antibody 2.3 IU/mL (0.0-1.0 IU/mL). Further history revealed fatigue, academic decline and polysomnograpy confirmed obstructive sleep apnea a couple of months prior to presentation. Levothyroxine replacement therapy was initiated at 25 mcg and dose was slowly increased over several weeks. 3 months later TSH level was 38.76 microIU/mL, Free T4 level normalized at 0.9 ng/dL and creatine kinase level normalized at 91 units/L (<143 units/L). Patient reported resolution of her myopathic symptoms and sleep apnea. Conclusion: This is first pediatric case report of rhabdomyolysis and sleep apnea due to hypothyroidism. Hypothyroidism should be considered in the differential diagnosis of rhabdomyolysis, especially if etiology of myopathy is unknown. Prompt thyroxine replacement can prevent further episodes of rhabdomyolysis and in this case also prevented long term complications and morbidity associated with sleep apnea. References: 1. Kisakol G et al. Rhabdomyolysis in a patient with hypothyroidism. Endocrine Journal. 2003;50(2):221-223.