Unmasking Neurosarcoidosis in a Patient With Acute Meningitis Features

Neurosarcoidosis is a rare disorder that may mimic infectious, inflammatory, and neoplastic conditions, therefore making diagnosis challenging. We report the case of a 32-year-old man with a background history of Crohn's disease treated with Adalimumab who presented with a 10-day history of worsening headache, confusion, and new-onset seizures. He also experienced transient sensory changes with one episode of fever. Neurological examination was unremarkable. Given his immunosuppressed condition, empirical treatment for meningoencephalitis was initiated. Initial CT scan of the brain was normal, while the first lumbar puncture demonstrated mild pleocytosis (18 × 10⁶/L, predominantly lymphocytic) but negative cultures. MRI scan of the brain revealed multifocal white matter lesions, initially suggestive of demyelination. A second lumbar puncture showed a significant rise in white cell count (110 × 10⁶/L, predominantly lymphocytic), but infectious and autoimmune screens remained negative. Given a persistent headache despite broad-spectrum antimicrobials, further workup was pursued. CT venography excluded venous sinus thrombosis. Surprisingly, systemic imaging revealed bilateral hilar and mediastinal lymphadenopathy. Endobronchial ultrasound-guided biopsy confirmed non-caseating granulomatous inflammation consistent with sarcoidosis, with no evidence of lymphoma or tuberculosis. We requested CSF angiotensin-converting enzyme levels retrospectively, and the result was elevated, further supporting the diagnosis of neurosarcoidosis. After multidisciplinary team review, high-dose intravenous methylprednisolone was commenced, followed by an oral prednisolone taper, leading to significant symptomatic improvement. This case highlights the complex diagnostic pathway of neurosarcoidosis, particularly in immunosuppressed patients, where infection is the predominant concern. The overlapping clinical and radiological features with meningoencephalitis and demyelinating disease emphasise the need to consider neurosarcoidosis in the differential diagnosis. Early multidisciplinary involvement, systematic exclusion of infection and malignancy, and timely initiation of immunosuppression were critical to achieving a favourable outcome in this case. Clinicians should maintain a high suspicion for neurosarcoidosis in patients presenting with atypical neurological features, as early recognition and treatment may substantially alter prognosis.