Histologic and cytologic bone marrow findings in dogs with suspected precursor-targeted immune-mediated anemia and associated phagocytosis of erythroid precursors.

BACKGROUND: Precursor-targeted immune-mediated anemia (PIMA) has been suspected in dogs with nonregenerative anemia and bone marrow findings varying from erythroid hyperplasia to pure red cell aplasia. Phagocytosis of erythroid precursors/rubriphagocytosis (RP) reported in some affected dogs suggests a destructive component to the pathogenesis of PIMA.

OBJECTIVES: The purpose of the study was to characterize laboratory and clinical findings in dogs with suspected PIMA and RP, with emphasis on cytologic and histologic bone marrow findings.

METHODS: Dogs with PIMA and RP were identified by review of paired bone marrow aspirate and core biopsy slides collected over a 4-year period. Samples were systematically assessed and characterized along with other pertinent laboratory data and clinical findings.

RESULTS: Twenty-five dogs met criteria for PIMA and had RP that was relatively stage-selective. Erythropoiesis was expanded to the stage of erythroid precursors undergoing most prominent phagocytosis, yielding patterns characterized by a hypo-, normo-, or hypercellular erythroid lineage. A 4th pattern involved severe collagen myelofibrosis, and there was a spectrum of mild to severe collagen myelofibrosis overall. Evidence of immune-mediated hemolysis was rare. Immunosuppressive therapy was associated with remission in 77% of dogs treated for at least the median response time of 2 months.

CONCLUSIONS: Bone marrow patterns in dogs fulfilling criteria for PIMA were aligned with stage-selective phagocytosis of erythroid precursors and the development of collagen myelofibrosis, common in dogs with PIMA. Recognition of these patterns and detection of RP facilitates diagnosis of PIMA, and slow response to immunosuppressive therapy warrants further investigation into its pathogenesis.