Anti-mGluR encephalitis: case series and literature review

INTRODUCTION: Anti-metabotropic glutamate receptors (mGluR) encephalitis is a rare form of autoimmune encephalitis (AE) with a very limited number of documented cases. OBJECTIVE: To report detailed characteristics of a case series of patients with anti-mGluR encephalitis and perform literature review of previously described cases. METHODS: We described clinical data from a case series of anti-mGluR patients, including clinical presentation, paraclinical findings and response to treatment. Moreover, we performed a literature review according to PRISMA to identify already described cases. RESULTS: In our hospital we identified eight patients tested positive for anti-mGluR antibodies (1 for anti-mglur1, 1 for anti-mglur2 and 6 for anti-mglur2) either cerebrospinal fluid or serum. In most cases, brain magnetic resonance imaging (MRI) was unremarkable (at early stage) and most patients showed marked improvement after immunotherapy. Literature review allowed us to further identify 36 cases of anti-mGluR1 AE, 8 cases of anti-mGluR2 AE, 34 cases of anti-mGluR5 AE. Overall, 53(%), 13 (%) and 69(%) of patients with anti-mGluR1, anti-mGluR2 and anti-mGluR5, respectively, were male. The mean age of onset was respectively 51, 37 and 38. Patients with anti-mGLUR1 and anti-mGLur2 mainly manifested ataxia, while those with anti-mGLUR5 antibodies manifested psychiatric symptoms. In patients with anti-mGluR5 AE, associations with Hodgkin’s lymphoma (HL), other antibodies associated with AE and infectious triggers were frequent. CONCLUSION: Anti-mGluR AE may present with heterogenous manifestations, according to the subtype of antibody. Early immunotherapy often improves outcomes, though some cases may relapse or develop cerebellar atrophy. Long-term follow-up is necessary, and underlying tumors—particularly HL in anti-mGluR5 AE—should be monitored.