Expanding the Spectrum: Isolated Acute Diencephalitis as the Initial Manifestation of Neuromyelitis Optica Spectrum Disorder.

Diencephalic syndrome is a rare clinical variant of neuromyelitis optica spectrum disorder (NMOSD), observed in approximately 3.4% of presentations. Its hallmark features include endocrine and sleep-wake disturbances such as syndrome of inappropriate antidiuretic hormone secretion (SIADH), hypothermia, narcolepsy, daytime somnolence, and appetite dysregulation.1 We report a case of NMOSD presenting as an isolated acute diencephalic syndrome, a rare and diagnostically challenging initial manifestation. This case underscores the importance of considering NMOSD even in the absence of typical optic neuritis or longitudinally extensive transverse myelitis.