Bone marrow mastocytosis in dogs with myelosuppressive monocytic ehrlichiosis (Ehrlichia canis): a retrospective study

Background: Bone marrow mastocytosis has been reported rarely in naturally occurring canine monocytic ehrlichiosis (CME). Objectives: The aims of the present study were to estimate the prevalence and magnitude of bone marrow mastocytosis in a case series of dogs with natural CME and to assess the association, if any, between mastocytosis and the clinical severity of the disease. Methods: Seventy-six dogs with confirmed CME (Ehrlichia canis) were included in the study. Affected dogs were allocated into group A (n=51) without bone marrow hypoplasia and group B (n=25) with bone marrow hypoplasia. Twenty clinically healthy Beagles not previously exposed to E canis served as controls (group C). The main inclusion criteria for group A were documentation of normocellular to hypercellular bone marrow and complete clinical cure following a 4-week treatment with doxycycline, while those for group B were bone marrow hypoplasia and lack of response to doxycycline. Bone marrow aspirate smears from all 96 dogs were Giemsa-stained and examined for the presence of mast cells, which were calculated as a percentage of 1000 nucleated cells (NCs). The prevalence of mastocytosis was compared among the 3 groups by the Pearson's chi-square test. Results: Bone marrow mastocytosis (>0.1% of NCs) was found in 5 (20%) dogs in group B (range, 0.5-2.5% of NCs; median, 1% of NCs). One dog in each of groups A and C had 0.1% mast cells in the marrow. The prevalence of bone marrow mastocytosis in dogs in group B was significantly higher (P= .004) than in groups A and C. Conclusion: Bone marrow mastocytosis can be seen in a substantial number of dogs with E canis–induced myelosuppression.