SIGNALMENT: 14-year-old female spayed Domestic Longhair
HISTORY: No clinical information provided. Regenerative anemia (HCT=22.9%, Reticulocytes = 58,000 cells/uL [3000-50,000]). WBC= 53,600 cells/uL; 13,936 cells/uL reported in the unclassified category. Neutrophils 32,160 cells/uL, monocytes 1072 cells/uL. Normal platelet concentration.
SOURCE: Blood smear
LEUKOCYTES: There is an expanded population of large, discrete round cells that comprise 26% of the differential. These cells have nuclei approximately 2-3 rbc’s in diameter, with finely stippled chromatin and prominent single basophilic nucleoli. The cells have a moderate to abundant volume of pale blue cytoplasm, that frequently contains diffuse granules that vary from fine, to more chunky. The granules frequently overlay the nucleus of the cell. These cells confirm round cell neoplasia in the patient, and the morphology of the cells is highly supportive for mast cells and mastocytemia, with atypical granular lymphocytes considered less likely. Slides have been submitted for Toluidine Blue staining to investigate the suspicion for mast cell origin. Correlate also with clinical findings, including any mass lesions within the gastrointestinal tract or spleen etc. The neutrophilia and monocytosis also are verified, confirming a concurrent inflammatory response, and there is an increased number of basophils, which can be seen as a paraneoplastic response in both mast cell neoplasia and lymphoma.
ERYTHROCYTES: Red blood cell density is decreased, consistent with the patient’s anemia. There is a mild increase in polychromatophils, consistent with the increased reticulocyte concentration, and a regenerative response by the bone marrow. No hemotropic organisms or evidence of oxidative damage are seen. Correlate with any clinical evidence of hemolysis or hemorrhage in the patient, and serial monitoring of the erythrogram also is recommended.
PLATELETS: No abnormalities detected.
Mastocytemia with inflammation and regenerative anemia
The Toluidine Blue stain is positive, confirming mast cells in circulation .In cats, mastocytemia most commonly indicates underlying mast cell neoplasia, which may affect internal organs such as the gastrointestinal tract, spleen (visceral mast cell neoplasia), or the skin (cutaneous mast cell neoplasia). Only rarely is mastocytemia in cats associated with neoplasms other than mast cell tumors (such as lymphoma or hemangiosarcoma) or non-neoplastic conditions (such as chronic renal disease), with mast cells usually present in low numbers in circulation.
REFERENCES: Piviani M, Walton RM, Patel RT. Significance of mastocytemia in cats. Vet Clin Pathol 2013;42(1):4-10.
Andrew G. Burton, BVSc
Diplomate, American College of Veterinary Pathologists