What is your diagnosis? Unusual cells in the blood smear from a dog.

Abstract

A 3-year-old intact male Rottweiler dog was referred to the Companion Animal Clinic, School of Veterinary Medicine, Aristotle University of Thessaloniki, Greece with a history of intermittent diarrhea, splenomegaly, pancytopenia, and an established diagnosis of leishmaniasis 2 weeks previously, based on the identification of Leishmania spp. amastigotes in lymph node (LN) aspiration cytology. The dog was seronegative for Ehrlichia canis antibodies (Witness Ehrlichia, Zoetis, France). Upon admission, the dog was on allopurinol, miltefosine, and doxycycline treatment, and was up-to-date with vaccinations and parasite control. Physical examination revealed palpable splenomegaly. Complete blood count (ADVIA 120, Siemens Healthcare Diagnostics, Deerfield, USA) following a saphenous vein venipuncture (due to uncooperative behavior of the dog) revealed mild normocytic, normochromic and nonregenerative anemia (HCT: 28.4%, reference interval [RI] 37–55%), mild leukopenia (WBC: 5,800/μL, RI 6,000–17,000/μL), and moderate thrombocytopenia (platelets: 90,000/μl, RI 200,000–500,000/μl). Serum biochemical testing was unremarkable. Blood smears were prepared for routine microscopic evaluation (Figure 1A and B). In a single blood smear, a cluster of spindle-shaped cells was observed (Figure 1A and B). The cells exhibited elongated nuclei with a smooth chromatin pattern, nonprominent nucleoli, and mild basophilic cytoplasm, with discrete cytoplasmic borders. No cytomorphologic atypia was noticed. The cells were presumed to be of endothelial origin and the dog was scheduled for further investigation. No similar cells were found in several plain and buffy coat smears made from the same blood sample. Fine-needle aspiration cytology of the normally sized popliteal LN revealed several Leishmania spp. amastigotes extracellularly or within macrophages, with lymphoid and histiocytic hyperplasia. Bone marrow aspiration cytology smears were of normal cellularity with all hematopoietic lineages being sufficiently represented. No Leishmania spp. amastigotes or atypical cells were identified. Abdominal ultrasonography revealed splenomegaly of normal echotexture. On re-evaluation of the dog, 40 days postadmission, complete clinical and hematologic recovery was documented. No unusual cells were observed during the thorough evaluation of plain and buffy coat blood smears (review of 500 ×40 objective microscopic fields). Lateral chest radiographs were unremarkable. On day 110 postadmission, physical, hematologic (including review of blood smears), and biochemical examination were unremarkable. The dog was alive and doing well 1.5 years postadmission. Endothelial cells are not usually seen in blood smear evaluation and are believed to represent an incidental finding possibly due to dislodgment of cells from the endothelial cell layer of the vessel wall.1 To the best of the authors' knowledge, a similar finding has not been described previously in the dog. Endothelial cells have been demonstrated in blood smears from a cow and a few human patients.1-4 From a cytomorphologic perspective, the cells observed in this dog could be interpreted either as neoplastic mesenchymal cells or as endothelial cells. The fact that the cells were observed just once and in a single blood smear, and evidence of a neoplastic disease could not be established based on clinical, laboratory, and imaging evaluation throughout the follow-up period, suggests the benign endothelial origin of the cells. The latter hypothesis may further be supported by the fact that venipuncture was not undisturbed due to the minimal cooperation of the dog. The probability of visualizing endothelial cells may be increased if a blood smear is made from the first drop of blood in the needle hub4; however, in the present case, the blood smear was prepared from EDTA-anticoagulated blood. It is also unknown if leishmaniasis could have been associated with this cytologic finding.