Marked leucocytosis in a cat

SIGNALMENT

12-year-old, male neutered, Domestic Shorthair cat.

 

HISTORY

A cat presented to the veterinarian with a one week history of lethargy. Vomiting and a mild decrease in appetite were also reported by the owner. The cat has also recently started to defecate outside of the litter tray. His thirst and urination were normal. The cat was FeLV and FIV negative.

 

PHYSICAL EXAMINATION

On presentation a small, round mass was palpated in the cranial abdomen. Mild abdominal discomfort was also observed. The mucous membranes were pale pink. No other clinical signs were evident.


INVESTIGATION

Haematology

Haematology was performed and identified marked leucocytosis (75.36x10^9/L, reference interval, RI: 6.0-11.0x10^9/L) and  mild anaemia (haematocrit: 28%, RI: 30-44%). The leukocyte differential count was not determined by the analyser due to an abnormal leukocyte scattergram. Relevant blood smear findings are shown in Figure 1.

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Figure 1. Peripheral blood smear from a 12-year-old, male neutered, Domestic Shorthair cat. Hemacolor stain, 20x objective (A), 50x objective (B).
B.

Biochemistry

Biochemistry showed moderate hyperglycaemia (15.67 mmol/L, RI: 3.1-6.9 mmol/L). All other biochemistry parameters were within normal limits. Urinalysis was unremarkable.

 

Parasitology

Faecal examination was performed and it was negative.


Imaging

Abdominal ultrasound was performed and showed a small, round, hyperechogenic mass in the small intestine.

 

 

Cytology

Fine-needle aspiration (FNA) cytology of the intestinal mass was performed (Figure 2).

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Figure 2. FNA cytology of the intestinal mass from a 12-year-old, male neutered, Domestic Shorthair cat. Hemacolor stain, 20x objective (A), 50x objective (B).
B.

What is your interpretation of the clinicopathological findings?

 

What are your differential diagnoses?

INTERPRETATION OF THE RESULTS

Haematology

A high number of eosinophils was observed in the blood film. This population comprised of mostly mature cells (segmented eosinophils) with low numbers of immature ones (band eosinophils, metamyelocyte eosinophils, myelocyte eosinophils). The differential count was 12% neutrophils, 3% lymphocytes and 85% eosinophils. Erythrocytes were mostly normocytic and normochromic.

Interpretation: Marked leukocytosis due to extreme eosinophilia with immature eosinophils was most consistent with chronic eosinophilic leukaemia or hypereosinophilic syndrome. Paraneoplastic eosinophilia, although very unlikely, could not have been totally ruled out.

Mild nonregenerative, normocytic and normochromic anaemia was likely secondary to bone marrow neoplasia and/or chronic disease.

 

Biochemistry

Moderate hyperglycaemia was most likely related to excitation given lack of glucosuria.

 

Cytology

Cytological examination of the intestinal mass showed high numbers of eosinophils. Low to moderate numbers of lymphocytes were observed – mixed population of lymphoid with the predominance of small lymphocytes and few intermediate and large cells. Occasional nondegenerated neutrophils were also present. The background was clear and heavily blood contaminated. The cytology indicated the presence of eosinophilic infiltration which was likely secondary to myeloproliferative neoplasm / hypereosinophilic syndrome. Although, there was no evidence of an intestinal tumour in the sample examined, presence of neoplasia could not have been excluded without histopathology.

PRESUMED DIAGNOSIS: CHRONIC EOSINOPHILIC LEUKAEMIA / HYPEREOSINOPHILIC SYNDROME with secondary infiltration of the intestines

 

MANAGEMENT AND FOLLOW-UP

The owner refused further diagnostic work-up and oncology treatment. Only palliative therapy was administered. The cat was euthanised 2 weeks later because of poor general condition, anorexia and cachexia. Histopathology of post-mortem samples confirmed the presence of eosinophilic infiltration of the small intestine (Figure 3). Intestinal neoplasia was ruled out.

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Figure 3. Histology of the small intestine from a 12-year-old, male neutered, Domestic Shorthair cat showing eosinophilic infiltration. Haematoxylin and eosin stain, 40x objective.
B.

SUMMARY
Chronic eosinophilic leukaemia is a neoplastic proliferation of bone marrow precursor cells which results in the presence of high numbers of mostly well-differentiated eosinophils in the peripheral blood. Whereas, hypereosinophilic syndrome is characterized by the presence of marked persistent eosinophilia of undetermined origin. Intestinal infiltration, which was observed in this case, can occur in both conditions. Differences between these two diseases are not well defined in veterinary species. Therefore, it is usually not possible to obtain a definitive diagnosis. In human medicine, most patients initially diagnosed with hypereosinophilic syndrome were reclassified as having a neoplastic condition when novel molecular and genetic tests became available. Bone marrow examination and flow cytometry, which could be useful in better characterization of the disease, were not performed in this case.

Common causes of an elevated eosinophil count (e.g. parasitism, allergy / hypersensitivity reaction, paraneoplastic syndrome) were ruled is this case based on the magnitude of eosinophilia and other clinical features.

Treatment options for chronic eosinophilic leukaemia / hypereosinophilic syndrome include prednisolone, hydroxyurea, hydroxycarbamide and interferon α. Prognosis is poor.