Seronegative neurobrucellosis—do we need new neurobrucellosis criteria?

•A rare case of a seronegative relapse of neurobrucellosis is reported.•Seronegative neurobrucellosis represents a diagnostic challenge.•Oligoclonal bands and a cerebrospinal fluid agglutination test proved essential in diagnosis.•Neurobrucellosis diagnostic criteria should be established. Neurobrucellosis presents in various clinical forms and should always be considered in neurological patients in highly endemic areas such as the Mediterranean basin. Establishing a diagnosis can be challenging since serological testing can sometimes yield negative results. We present a rare case of a seronegative relapse of neurobrucellosis in a patient who had been successfully treated for systemic brucellosis. Oligoclonal bands, an agglutination test, and 16S rRNA sequencing of cerebrospinal fluid proved essential in unmasking a confined central nervous system relapse. This case reinforces the need for establishing diagnostic criteria for neurobrucellosis, which could potentially include oligoclonal bands and an agglutination test on the cerebrospinal fluid.