Brain Atrophy in Dogs With Meningoencephalitis of Unknown Origin

ABSTRACT Background Information regarding repeat magnetic resonance imaging (MRI) findings in dogs with meningoencephalitis of unknown origin (MUO) is sparse and it is unknown whether brain atrophy occurs. Objectives To determine whether brain atrophy occurs in MUO and evaluate if there is an association between atrophy and survival or relapse. Animals Twenty‐three dogs diagnosed with MUO that underwent MRI of the brain on two occasions at least six months apart. Methods Retrospective study. Interthalamic adhesion thickness to brain height ratio (ITr), lateral ventricle to brain height ratio (LVr), interthalamic adhesion thickness/brain height to lateral ventricle/brain height (ITr/LVr), bicaudate ratio (BCR) and total parenchymal brain volume (TPBV) were measured on both MRI studies and compared. Results Thirteen dogs relapsed and four died during the study period. Median time between MRIs was 12 months, and only one imaging study (1/23) was considered normal on the second scan. All MRI variables measured significantly changed between imaging studies, but only higher TPBV was associated with increased survival (OR = 1.59, CI = 1.006–2.51, p = 0.047); no variables were found to be associated with relapse. New lesions were identified in six dogs (four of which also showed contrast enhancing lesions), with 5/6 of these dogs subsequently relapsing. Conclusions and Clinical Importance Brain atrophy likely occurs in dogs with MUO and is associated with worse outcomes. Clinical relapse might be likely in dogs with new or contrast‐enhancing lesions on repeat MRI, so more aggressive treatment should be considered in these dogs.