Neurosarcoidosis as a rapidly progressive dementia associated with normal pressure hydrocephalus.

Neurosarcoidosis (NS) is a rare subtype of sarcoidosis with a poor prognosis and diverse clinical presentations that often poses a diagnostic and therapeutic challenge. We describe the case of a 53-year-old male with an initial diagnosis of lingual sarcoidosis, who subsequently developed ataxia and rapidly progressive cognitive impairment. A lumbar puncture revealed hypoglycorrhachia, hyperproteinorrachia, lymphocytic pleocytosis, and elevated IL-6 levels (600 pg/ml). Cerebrospinal fluid flow cytometry showed an elevated CD4 lymphocyte concentration and a CD4+/CD8+ ratio of 3.91, indicative of NS. Brain MRI showed hyperintense periventricular and subcortical lesions on FLAIR/T2 resembling progressive multifocal leukoencephalopathy (PML), although negative PCR for JC virus ruled out the differential diagnosis. Following a favorable evolutionary course with corticosteroid pulses, the patient relapsed with normotensive hydrocephalus, treated with immunosuppressants and ventriculoperitoneal shunting with a good response to date. This case underscores the importance of maintaining a high index of suspicion for NS in individuals with sarcoidosis and neurologic symptoms. In these cases, cerebrospinal fluid biomarkers such as IL-6 and CD4+/CD8+ ratio are essential to guide the diagnosis. Furthermore, it highlights that hydrocephalus is a rare complication and requires a multidisciplinary approach, including medical and neurosurgical treatment.