Secondary outcome measures in dogs with normal and abnormal MRI.

Survival in dogs with meningoencephalomyelitis of unknown etiology with and without lesions detected by magnetic resonance imaging

Arielle Ostrager, R. Timothy Bentley, Melissa J. Lewis, George E. Moore

Background
Meningoencephalomyelitis of unknown etiology (MUE) in dogs has variable prognosis, often depending on diagnostic imaging findings. While lesions detectable by MRI are common, some cases present with normal MRI, raising questions about their prognostic significance. This study aimed to compare survival and outcomes in MUE cases with and without MRI lesions, hypothesizing better outcomes in the normal MRI group.

Methods
A retrospective analysis of 73 dogs diagnosed with MUE at a veterinary hospital (2010–2020) was conducted. Dogs were categorized based on MRI findings as either normal or abnormal. Data on clinical presentation, MRI findings, cerebrospinal fluid (CSF) analysis, treatment protocols, survival, and remission/relapse rates were collected. Statistical analyses, including Kaplan-Meier survival analysis and multivariate Cox regression, assessed prognostic factors and group differences.

Results
-Study Sample: Of 73 dogs, 19 had normal MRI findings, and 54 had abnormal MRI findings. Median follow-up durations were 9 and 12 months, respectively.

-Primary Outcome:
-Disease-related deaths occurred in 5% of normal MRI cases and 33% of abnormal MRI cases (p = 0.02).
-Median survival exceeded 107 months in both groups, but survival was significantly better in the normal MRI group (p = 0.02).

-Secondary Outcomes:
-Remission was achieved in 68% of normal MRI cases and 53% of abnormal MRI cases.
-Relapse rates, early and late, did not significantly differ between groups.

-Prognostic Indicators:
-Abnormal MRI findings were significantly associated with increased risk of death (hazard ratio = 7.71; p = 0.047).
-CSF total nucleated cell count was higher in the abnormal MRI group (p = 0.04).
-Use of secondary immunosuppressive treatments was more frequent in the abnormal MRI group (p = 0.01).

Limitations
This retrospective study had variability in treatment protocols and relied on owner-reported follow-up data for some cases, which could introduce biases. Additionally, requiring CSF pleocytosis for inclusion likely excluded severe cases with mass effect or clinical signs preventing CSF collection.

Conclusions
Dogs with MUE and normal MRI findings exhibited lower disease-related mortality compared to those with abnormal MRI findings, highlighting the prognostic relevance of MRI results. These findings underscore MRI's potential role as a biomarker of disease severity in MUE.

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