This page is for referring vets. If you are a pet owner please click here.

Case Report:Erythroblastic Leukaemia in a Domestic Longhair Cat

A three year old, female neutered, domestic longhair cat was presented with acute onset collapse and pallor. Prior to this the cat had been bright and alert. However, significant weight loss (from 3.25kg to 2.75kg;15% reduction) had been documented over the preceding month in the referring veterinarian’s records. There was no history of trauma and there was no known access to toxins or drugs.

fig. 1 – physical examination revealed inability to stand and a poor body condition.

On physical examination the cat was in poor body condition (BCS 1/5; fig. 1) and was weak and unable to stand. The mucous membranes were very pale and the capillary refill time could not be appreciated. The breathing was shallow and tachypnoeic (80bpm) and there was a 3/6 systolic heart murmur. The heart rate was mildly elevated at 240bpm with sinus rhythm. The pulse quality was strong and there was no pulse deficit. The rectal temperature was slightly low at 99.9oF. The remainder of the routine clinical examination was unremarkable. The systolic blood pressure was 150mmHg and ophthalmoscopic examination was unremarkable.

The cat was assessed to be well hydrated so fluids were not administered immediately but an intravenous catheter was placed in case emergency IV access was required. Given the tachycardia oxygen supplementation was given and because of the mild hypothermia the cat was placed in an incubator. Blood was taken for baseline analysis (table 1, below) revealing severe anaemia.

Table 1: Baseline blood results

pH 7.38   7.35-7.45
Sodium 150.2 mmol/l 142-150
Potassium 3.86 mmol/l 3.4-4.9
Ionised calcium 1.37 mmol/l 1.12-1.40
Chloride 110 mmol/l 106-127
Urea 8.2 mmol/l 10-26
Glucose 64 mmol/l 60-115
PCV 8.9 % 35-50

Blood smear: No evidence of aniscocytosis or polychromasia, some nucleated red blood cells present, few platelets seen.

Following an improvement in the cat’s clinical status, further blood was submitted for full haematology (table 2, below).

Table 2: Initial haematology results

Hb N/A   8.0-15.0
PCV 6.0 % 25.0-45.0
RBC 1.00 x1012/l 5.50-10.00
MCV 67.4 fl 40.0-55.0
MCH N/A pg 12.5-17.0
MCHC N/A g/dl 30.0-35.0
Plt 10 x109/l 200-700
nRBC 22.3 x109/l  
Metamyelocytes 0.22 x109/l 0.00-0.30
Neutrophils 2.23 x109/l 2.50-13.20
Lymphocytes 3.07 x109/l 1.50-7.00
Monocytes 0.00 x109/l 0.00-0.90
Eosinophils 0.06 x109/l 0.00-2.00
Basophils 0.00 x109/l 0.00-0.10

Lipaemic sample gave falsely high Hb. Hb, MCH and MCHC therefore not reported. Spun PCV performed.

Film comment: Thrombocytopenia. Normocytic and normochromic anaemia. High MCV due to red cell agglutination. The nucleated red cells are intermediate and late normoblasts.

fig. 2 - blood smear cytology showing nucleated red blood cells.

This confirmed a severe, non-regenerative anaemia with a significant number of circulating nucleated red blood cells (fig. 2).

There was also marked thrombocytopenia and

a mild neutropaenia. Serum biochemistry revealed a moderate elevation in liver enzymes and creatine kinase along with mild hypoproteinaemia.  Infectious disease screening (feline infectious anaemia PCR, FIV ELISA and FeLV ELISA) was negative as was Coombs testing. Coagulation times (PT/APTT) were within normal limits and urinalysis was unremarkable. These results were highly suspicious for a primary bone marrow disorder.

A blood transfusion was performed (50ml type A whole blood) following which the haematocrit increased from 6.0% to 13.2% and the platelet count increased from 10×109/l to 48×109/l (table 3, below).

Table 3: Follow-up haematology results

Reticulocytes 0.02 x1012/l  
Hb 5.41   8.0-15.0
Hct 19.7 % 25.0-45.0
RBC 2.98 x1012/l 5.50-10.00
MCV 66.2 fl 40.0-55.0
MCH 18.2 pg 12.5-17.0
MCHC 27.4 g/dl 30.0-35.0
Plt 48 x109/l 200-700
nRBC 4.7 x109/l  
White blood cells 9.7 x109/l 4.9-19.0
Neutrophils 5.35 x109/l 2.50-13.20
Lymphocytes 2.43 x109/l 1.50-7.00
Monocytes 1.07 x109/l 0.00-0.90
Eosinophils 0.88 x109/l 0.00-2.00
Basophils 0.00 x109/l 0.00-0.10

A course of doxycyline (10mg/kg po sid) was also started in case of haemotropic mycoplasma infection whilst awaiting the infectious disease screening results. 24 hours later the cat appeared much brighter. Diagnostic imaging (lateral thoracic and lateral abdominal radiography and abdominal ultrasonography) was unremarkable so the cat was anaesthetised for bone marrow aspiration and biopsy. Bone marrow cytology and histopathology were both indicative of acute erythroblastic leukaemia and FeLV PCR of the bone marrow sample was negative.

Chemotherapy induction was instigated using cytosine arabinoside (50mg/m2 iv bid for 4 days) and doxorubicin (10mg/m2 iv sid for 3 days). Blood samples were taken pre-treatment and then daily during treatment for haematological monitoring. Several days into the induction marked neutropaenia was noted (0.27×109/l) and the thrombocytopenia had worsened (27×109/l). Chemotherapy was therefore suspended and prophylactic antibiotics were given (amoxicillin-clavulanate 50mg q12h P.O.). A week later the neutrophil count had normalised and the chemotherapy induction was completed. The PCV and platelet count remained low (10.8% and 40×109/l respectively) and, following cross matching, a repeat blood transfusion was given before discharge. The maintenance chemotherapy protocol was cytosine arabinoside (50mg/m2 sc – two doses 12hours apart once weekly) and doxorubicin (10mg/m2 iv every 3 weeks). Blood was taken weekly for haematological monitoring.

Two weeks following discharge the haematocrit had gradually increased to 19.7% and the platelet count had improved (60×109/l). The cat continued to do well clinically, remaining bright with a good appetite and the haematology results remained stable. However, two months later the cat became acutely weak and dyspnoeic. The PCV at this time was 9%. Cross matches were performed with several donor cats but strong agglutination was evident in all the samples

Since repeat transfusion was unlikely to be successful the owners opted for euthanasia at this stage.

Erythroblastic leukaemia is a myeloproliferative disease which is characterised by malignant transformation and excessive proliferation of erythroid precursors in the bone marrow. As in this patient, it generally results in severe non-regenerative anaemia with nucleated erythrocytes present in the peripheral circulation. Erythroblastic leukaemia is rare in cats. In the few published case reports, concurrent FeLV infection is a common finding but this did not appear to be an inciting factor in this cat. The prognosis for acute non-lymphoblastic leukaemias is generally poor and euthanasia is often performed at the time of diagnosis. The two-month survival time seen in this cat seems favourable compared with survival times documented in previous case reports but it is impossible to compare efficacies due to a paucity of case numbers.