A Reversible Etiology of Progressive Motor Decline in a Previously Healthy Child.

We describe the clinical presentation and evaluation of a 10-year-old boy who presented to our medical center with years of progressive proximal muscle weakness, muscle atrophy, and weight loss. In addition to a myopathic phenotype, he was found to have tachycardia, tremor, and learning difficulties. Electromyography revealed chronic myopathic changes and laboratory screening was notable for undetectable thyroid stimulating hormone. Follow-up testing revealed elevated thyroid peroxidase antibodies and thyroid stimulating immunoglobulins. Ultrasound examination revealed an enlarged heterogeneous thyroid gland. Four weeks after treatment with atenolol and methimazole, his strength and cognition began to improve. This case highlights the importance of evaluating for potentially reversible toxic-metabolic etiologies in children presenting with any progressive neurologic symptoms.