ABSTRACT: Blue, a 12-year-old, male neutered Russian Blue cat, weighing 5.24kg, was presented to the emergency clinic after having a seizure. The cat was fully vaccinated, and had previously been in perfect health, although the owner reported that it had been "off colour” for the past week. There was no known exposure to poisonous substances, although as the cat had free access to the outdoors, this could not be ruled out entirely.

Clinical picture

On clinical examination, Blue was ataxic with occasional mouth breathing. Temperature, pulse and respiration were normal, mucous membranes were dark pink and moist. The results of in-house haematology can be seen in Table 1.

The patient was started on intravenous fluids and 2.5mg diazepam to control the seizures. He was then referred to The Oxford Cat Clinic for further investigations of the polycythaemia (Table 2).

On presentation at The Oxford Cat Clinic, Blue still showed signs of ataxia (exaggerated gait), although this was thought to be associated with the diazepam. Both nictitating membranes were slightly prolapsed and injected (Figure 1). Ophthalmic examination showed that the retinas were normal.

Figure 1: Injected membranes

Thoracic auscultation and abdominal palpation revealed no abnormalities; mucous membranes were very dark red. Systemic blood pressure, measured using the Doppler method, was 150 mmHg (normal range 120 – 170). The cat was thought to be in good body condition (body condition score of three out of five).

Diagnostic tests

General anaesthesia was induced, using 30mg propofol (Propoflo – Abbott) by slow intravenous injection, and maintained with isoflurane (Isocare – Animalcare) vaporised in oxygen (the patient had received diazepam earlier in the day, so no further premedication was necessary).

Radiographs of the thorax and abdomen were performed to look for signs of neoplasia, followed by ultrasonography (including a heart scan). Ultrasound- guided fine-needle aspirates were taken from the kidneys.

A blood sample was collected for full biochemical and haematological assessment, including reticulocyte count and erythropoietin assay (Table 3).

Diagnosis and prognosis

Serum total protein was within normal limits, which eliminated dehydration as a cause of the high PCV. Radiography, ultrasonography and kidney aspirates revealed no sign of neoplasia or cardiopulmonary disease; reticulocyte and erythropoietin (EPO) levels were within normal range, making secondary polycythaemia unlikely.

Haematology revealed raised haemoglobin, haematocrit (PCV), red blood cells and thrombocytes (platelets) as documented previously by the referring vets.

In view of these findings, the veterinary surgeon gave a diagnosis of polycythaemia rubra vera (P.Vera). The prognosis of P.Vera is good with appropriate management. Affected animals can have extremely long survival times (greater than two years) when treated with chemotherapy (with or without phlebotomy).

Treatment

Initial treatment involved phlebotomy (venipuncture for the withdrawal of blood) to lower blood viscosity and, therefore, prevent further seizures. As large volumes of blood were being withdrawn (10 ml/kg/day), the procedure was performed while the patient was still under general anaesthesia on day one.

The same technique was employed as for normal blood sampling – aseptic technique on the jugular vein – a wide bore needle (18G butterfly needle) was required owing to the high viscosity of the blood. Intravenous fluids (Hartmanns –   Animalcare) were administered at an equivalent rate of 10 ml/kg/hour during the procedure, as sudden decreases in blood volume can result in marked hypotension. This was repeated on day two under sedation, using 5 mg/kg ketamine (Ketaset – Fort Dodge) and 0.25mg/kg midazolam (Hypnovel – Roche, used off licence).

In-house PCVs (IDEXX – Stat Spin) were performed to monitor response to treatment (Figure 2 & Table 4).

Figure 2: Taking a PCV reading

Blue was closely monitored after each treatment for further seizures or adverse reactions to the phlebotomies – hypovolaemia or hypotension, for example –   but he responded well to treatment.

Once the patient was stabilised, and a definitive diagnosis was secured based on the laboratory results, chemotherapy treatment was started, using hydroxyurea (Hydrea – Bristol Myers) orally at an initial dose of 25mg/kg every other day. Side effects of this drug include neutropaenia, anaemia and (dose- dependent) methaemoglobinaemia; therefore the cat remained at the Clinic for the first week of treatment for observation and PCV monitoring (Table 4).

Follow-up and outcome

The patient was discharged, but revisited the Clinic two weeks later for haematology, which revealed a good response to treatment. Check ups were initially every four to eight weeks and the dose of hydroxyurea altered according to the prevailing PCV and neutrophil counts.

No further phlebotomies were necessary. Blue continues to do well on the treatment, and at the time of writing, is living a full and healthy life 20 months after diagnosis (Figure 3).

Figure 3: Blue enjoying life after treatment, whilst waiting for his fur to grow back.

Discussion

Most cases of absolute polycythaemia in cats are primary, however secondary causes need to be ruled out before making a diagnosis of P.Vera.2 There was no evidence of cardiopulmonary disease and erythropoietin levels were normal, which made secondary polycythaemia unlike
ly. Blood gas analysis can be used to rule out hypoxia, although it was not performed in this case.

The increase in blood viscosity (hyperviscosity) caused the dark pink mucous membranes and seizures seen on presentation. Phlebotomy was, therefore, required as soon as possible to prevent further seizures and stabilise the patient. Hyperviscosity can make phlebotomy impossible; leeches have been used in some cases in order to decrease the PCV.3

Nursing care involved 24-hour observation to monitor the patient and check for any abnormal response to treatment. Owing to the polycythaemia, Blue bruised very easily (Figure 4); clotting times were checked and found to be normal. Arnica cream was applied to affected areas to help alleviate the bruising. Periodic bleedings could theoretically lead to iron deficiency; however, because of the good response to treatment, prolonged phlebotomies were not required in this case.4

Figure 4: Bruising post phlebotomy

Hydroxyurea is currently an unlicensed drug for animals and is only available in 500mg capsules. It is teratogenic and requires careful handling. As the capsules must not be split, the drug can be recompounded by a pharmacist, according to the dose required. Owners must be made aware of all of this information and give permission for its use.

Clients who have to give chemotherapy drugs at home must be given clear instructions (written as well as verbal) regarding administration, handling and storage of the drug. They should also be advised on the handling of waste (such as urine and faeces), but this will vary depending on the drug used and route and rate of excretion. 2

Acknowledgements

Thank you to Caroline Blundell and Martha Cannor for your help and support in producing this article

Author

Joanne Mercado

DipAVN(Med) VN MBVNA

Jo started her nursing career in a busy, mixed animal practice in November 1995, and qualified from Farnborough College of Technology in 2000. She moved to referral practice in 2005, gained her Diploma in 2008, and currently works at The Oxford Cat Clinic, a first and second opinion practice for cats only!

References

1.   NELSON, R. W., COUTO, C. G. (1998) Small Animal Internal Medicine 2nd edition, Missouri, USA Mosby

2.   WATSON, A. D. J., MOORE, A. S., HELFAND, S. C. (1994) Primary erythrocytosis in the cat: Treatment with hydroxyurea. Journal of Small Animal Practice 35(6): 320-325.

3.   NETT, C. S., ARNOLD, P., GLAUS, T. M. (2001) Leeching as initial treatment in a cat with polycythaemia vera. Journal of Small Animal Practice 42(1 1): 554-556.

4.   WEISER, M. G. (1994) Chapter 27 Disorders of Erythrocytes and Erythropoiesis In Sherding, R. G (1994) Cat D iseases and Clinical Management 2nc edition, USA. W B Saunders.

 

• VOL 25 • No10 • October 2010 • Veterinary Nursing Journal