Mumps Vaccine-Associated Aseptic Meningitis Complicated by Syndrome of Inappropriate Antidiuretic Hormone Secretion.

Mumps vaccine is generally safe; however, aseptic meningitis remains a rare but recognized adverse event. We report the case of a 15-year-old male who developed a progressive headache and hyponatremia, leading to a diagnosis of syndrome of inappropriate antidiuretic hormone secretion (SIADH). As his symptoms worsened, CSF analysis revealed pleocytosis with monocyte predominance and elevated protein levels, resulting in a diagnosis of aseptic meningitis.