ObjectiveTo report a patient with neurobrucellosis mimicking primary CNS vasculitis (PCNSV) diagnosed by CSF metagenomic next-generation sequencing (mNGS).MethodsA 32-year-old male patient with a prior stroke developed headache, dizziness, fever, and memory complaints in the past 30 days. Physical examination was unremarkable except for slight apathy. He was investigated with brain MRI, cerebral digital angiography, CSF analysis with mNGS, and brain biopsy.ResultsAn examination of the brain MRI showed a left nucleocapsular gliosis compatible with prior stroke; MR angiogram showed circular enhancement of distal branches of the middle cerebral arteries. Digital angiogram revealed stenosis of intracranial carotid arteries and the left middle cerebral artery. The CSF disclosed 42 cells/mm3, 46 mg/dL of glucose, and 82 mg/dL of protein. Brain biopsy showed a chronic leptomeningeal inflammatory process, not fulfilling criteria for PCNSV. mNGS revealed the presence ofBrucellasp. genetic material. He was treated with antibiotics with full remission of systemic and neurologic symptoms.DiscussionBrucellosis is an endemic disease in developing countries and may mimic PCNSV. Our patient fulfilled the criteria for possible PCNSV; however, brain biopsy was inconsistent with PCNSV, and CSF mNGS disclosed neurobrucellosis. This case illustrates the importance of CSF mNGS in the differential diagnosis of CNS vasculitis.

Context Primary angiitis of the central nervous system (PACNS) is characterized by the inflammation of small and medium CNS arteries; the clinical manifestations include headache, cognitive impairment and focal neurological deficits. The gold standard test for diagnosis is brain biopsy. Neurobrucellosis is an infection associated with cattle farming, which leads to neurological and psychiatric symptoms. We report a case of neurobrucellosis mimicking PACNS. Case report Male, 32 years old, with fever, headache, dizziness and cognitive impairments for 30 days. History of stroke 2 years before, with mild sequelae right hemiparesis; investigation showed suspected intracranial dissection. On physical examination, he had apathy, preserved strength, reduced reflexes with plantar flexor responses. General laboratory tests, autoantibodies and serology were normal. Brain MRI showed deep left nucleocapsular gliosis and cerebral angiography revealed stenosis of the ICA and MCA. CSF showed 42 cells/ mm³, glucose 46 mg/dL, protein 82 mg/dL. Blood PCR was negative for Brucella. Immunophenotyping of the CSF and PET-CT excluded neoplasia. Brain biopsy was inconclusive for vasculitis. Metagenomic analysis of the CSF detected 78% of Brucella genetic material. Serum agglutination test was 1:40 for brucella. Conclusions PACNS is diagnosed by exclusion. The patient filled criteria for possible PACNS, image compatible with vascular stenosis, but inconclusive brain biopsy. Brucellosis is an endemic disease in underdeveloped countries that can present as CNS vasculitis. Metagenomic analysis allows the detection of different pathogens using a single method. The case illustrates the use of metagenomics in rare diseases characterized by vasculitis, with change in clinical outcomes and conduct.