Clinical Reasoning: A 10-Year-Old Boy With Progressive Tremor, Insomnia, and Autonomic Dysfunction.

A 10-year-old boy developed progressive tremor, insomnia, and autonomic dysfunction after an upper respiratory tract infection. Initial workup, including brain MRI, CSF analysis, and antibody screening, was unremarkable. By the third month of illness, brain MRI revealed multiple hyperintensities on fluid-attenuated inversion recovery sequences. Empiric immunotherapy led to partial clinical and radiologic improvement. However, neurologic deterioration continued despite subsequent immunosuppressive treatment, and follow-up imaging demonstrated progressive cerebral atrophy. 18F-fluorodeoxyglucose PET revealed marked bilateral thalamic hypometabolism, providing a pivotal clue that redirected the diagnostic approach. Definitive diagnosis was ultimately established through targeted genetic analysis. This case underscores the importance of maintaining a broad differential diagnosis in pediatric patients presenting with progressive neurologic decline, even in the context of transient inflammatory or immune-appearing features. It also highlights the diagnostic value of genetic testing when conventional investigations are inconclusive.