Brain Atrophy in Dogs With Meningoencephalitis of Unknown Origin.

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.