Nonvasculitic autoimmune inflammatory meningoencephalitis

Caselli and colleagues described five cases with encephalopathy, progressive cognitive decline, ataxia, abnormal CSF studies and steroid responsiveness, and proposed the term non‐vasculitic autoimmune inflammatory meningoencephalitis (NAIM). Many of these cases had brain biopsy showing mild leptomeningeal perivascular lymphocytic  inflammation ,  however, none of the cases had a post‐mortem. Nonvasculitic autoimmune mediated meningoencephalitis has been described in patients with Sjogren's syndrome, systemic lupus erythematosus and, more recently, with Hashimoto's disease. The present study is the first post‐mortem report of a case with a clinical diagnosis of NAIM. Neuropathological examination revealed a panencephalitis with intact vessel walls. T and B immunostaining showed a mixture of T and B cells. The findings were not consistent with other reported findings in collagen vascular diseases including Sjogren's syndrome, CNS vasculitis or Hashimoto's encephalopathy. There was no evidence of neoplasia, bacteria, acid‐fast bacilli, fungi or atypical infectious agents. This is the first post‐mortem report of a case with a clinical diagnosis of NAIM and demonstrates a panencephalitis without evidence of a vasculitis. The pathology seems unique, however, Sjogren and Hashimoto's encephalopathy might be variants of NAIM.