Relapsing meningoencephalitis of unknown origin in dogs results in changes in neuroanatomical localization, magnetic resonance imaging, and cerebrospinal fluid.

Abstract

OBJECTIVE: The purpose of this study was to provide a description of clinical neuroanatomical localization, MRI, and CSF in dogs with relapsing meningoencephalitis of unknown origin (MUO). METHODS: This was a multicenter, retrospective, observational descriptive study of dogs with a clinical diagnosis of presumptive MUO and relapse, with a full medical history and MRI scan at initial presentation and relapse. The study period was over 12 years (April 2011 to August 2023). RESULTS: 39 dogs with a clinical diagnosis of presumptive MUO and relapse were included. The clinical neuroanatomical localization differed between relapse and initial presentation in 22 of 39 cases (56%). The initial MRI changes were observed on nearly all MRIs at relapse (36 of 39 cases [92%]), and the majority (33 of 39 [85%]) of relapse MRIs had new lesions. New lesions with similar MRI characteristics occurred, especially in the parietal area. Lesions resolved more frequently in the brainstem and cerebellum. Cerebrospinal fluid nucleated cell count was lower at relapse compared to initial presentation (median change, 107 cells/µL; 95% CI, 11 to 1,217; P = .005), and relapse CSF showed lower lymphocyte counts. CONCLUSIONS: Cases of relapsing MUO show notable differences in neuroanatomical localization, MRI findings, and CSF characteristics compared to initial presentation. CLINICAL RELEVANCE: Repeat MRI and CSF analysis provides additional insights into disease progression, enabling potential treatment adjustments.