A case report of syndrome of inappropriate antidiuretic hormone secretion unveiling hypothalamic involvement in multiple system atrophy.

Syndrome of inappropriate antidiuretic hormone secretion (SIADH) and central fever are rare and underrecognized manifestations of multiple system atrophy (MSA). Here, we report a 66-year-old woman who presented with a progressively evolving combination of parkinsonian features and pronounced autonomic dysfunction, fulfilling the diagnostic criteria for clinically probable MSA. Notably, she also developed two uncommon comorbidities: euvolemic hypotonic hyponatremia fulfilling the diagnostic criteria for SIADH, alongside episodic fever refractory to antipyretics in the absence of infection, but responsive to environmental cooling, consistent with central fever. These uncommon comorbidities underscore the involvement of hypothalamic and neuroendocrine regulatory pathways in MSA. This case broadens the well-recognized non-motor clinical spectrum of MSA and emphasizes the importance of considering central mechanisms when evaluating unexplained hyponatremia or fever in MSA. Awareness of these atypical manifestations may facilitate early recognition, guide targeted homeostatic management, and ultimately improve the quality of clinical care in MSA.