Case Report: Necrotizing granulomas in the central nervous system: sarcoidosis masquerading as neurotuberculosis

Neurosarcoidosis (NS) can affect patients with or without any systemic involvement. Diagnosis of NS without lung involvement requires (i) a biopsy showing typical non-necrotizing granulomas and (ii) exclusion of tuberculosis by negative culture for M. tuberculosis and PCR amplification techniques. In the absence of microbiological infection, the diagnosis is challenging when granulomas are necrotizing mimicking tuberculosis on histology. We report two cases presenting neurological symptoms and radiological lesions that were concordant with the diagnosis of NS. Nevertheless, brain biopsy showed necrotizing granulomas. Antineutrophil cytoplasmic antibodies (ANCA) showed a negative finding. Given the biopsy results, we started anti-tuberculosis treatment despite negative mycobacterial test results. Lack of improvement suggested the diagnosis of necrotizing sarcoid granulomatosis (NSG). NSG usually presents granulomas, necrosis, and vasculitis, mostly in the lungs. However, these cases presented granulomas with extensive necrosis and vasculitis compatible with NSG strictly limited to the central nervous system. The final diagnosis was NS, as NSG is sometimes understood as presenting a pattern of sarcoidosis, a hypothesis supported by the sustained remission obtained under immunosuppressive treatment. Brain NSG should not rule out the diagnosis of NS and lead to the diagnosis of tuberculosis. NS or NSG should still be evoked, especially if microbiological and immunological investigations are negative and even if the central nervous system is the unique organ involved.