Evaluation of Hematologic Parameters in 40 Dogs Receiving Long- Term Cytarabine for Meningoencephalomyelitis of Unknown Etiology

Background: Cytarabine (CA) is a commonly used adjunctive therapy for meningoencephalomyelitis of unknown etiology (MUE). Reported hematologic side effects include leukopenia, thrombocytopenia, and anemia. These have historically been reported more frequently in veterinary or human oncology patients receiving CA at chemotherapeutic doses rather than in dogs treated for MUE. Frequent CBC monitoring is considered standard practice following treatment with CA, but the added cost and time of monitoring may be deterring factors for owners when choosing adjunctive MUE therapies. Hypothesis/Objectives – Our aim was to evaluate hematologic parameters in dogs treated long-term (>6 months) with CA within a therapeutic range of 200-400mg/m2 at a minimum of every 3-4 weeks for clinically diagnosed MUE with the goals of developing appropriate monitoring recommendations and reporting adverse effects (AE). We hypothesized that there would be minimal to no evidence of myelosuppression or other AE. Animals: 40 client-owned dogs with a clinical diagnosis of MUE. Methods: Multicenter retrospective study. Hemograms pre- and post-treatment with CA were evaluated for changes in blood cell counts. Non-hematologic AE were categorized by severity and potential cause. Results: No statistically significant cytopenias were seen. Non-hematologic AE potentially attributable to corticosteroids and CA therapy were reported in ten patients. One patient had mild AE directly attributable to CA. Conclusions and Clinical Importance: The use of corticosteroids and CA at the described dosages has infrequent effects on hematologic parameters and is safe for long-term use in dogs with MUE. Our results support a reduction in the frequency of CBC monitoring during MUE treatment with CA