Polycythaemia vera in cats: a patient care report

The patient (Sansa) was referred for abnormal neurological behavioural signs and was diagnosed with primary polycythaemia. Polycythaemia is an increase in erythrocyte concentration — normally displayed as an increase in the packed cell volume (PCV) and/or haematocrit (HCT), haemoglobin concentration or red blood cell count (RBC) (Stokol, 2017) — and polycythaemia vera is an erythrocyte myeloproliferative disorder (Beale, 2017).

Signalment

Species: Feline

Breed: Domestic Short Hair

Age: 2 years 6 months

Gender: Female (entire)

Weight: 3.42 kg (Figure 1).

History

The patient presented as an emergency for further investigation after abnormal neurological behavioural signs with one suspected seizure episode. Behaviours reported included: seeking dark places, swaying and sitting close to walls. Eating and drinking were normal with no episodes of vomiting or diarrhoea. On presentation, the patient was up-to-date with vaccinations, flea and deworming treatment and registered at a local first opinion veterinary practice.

Physical examination

Physical examination revealed a heart rate of 179 beats per minute (bpm), respiratory rate of 88 respirations per minute, and her mucous membranes and pads were congested. Thoracic auscultation was unremarkable with no heart murmur or gallop sound detected. Neurological examination revealed bilaterally dilated and unresponsive pupils; spontaneous nystagmus (involuntary, rapid and repetitive movement of the eyes) was not present and the remainder of the examination was unremarkable.

This patient was particularly stressed on arrival to the clinic, which was further demonstrated by the presenting tachypnoea. Flow by oxygen supplementation was trialled but the cat was so distressed that an oxygen cage was set up to allow the patient to settle. This improved the patient's respiratory rate, allowing time for assessment and preparation for further procedures. Minimal handling of dyspnoeic patients on arrival is essential to aid prognosis of any underlying conditions (Dickson et al, 2017). After some time in the oxygen cage, the tachypnoea improved; however, the neurological signs were still present.

Initial tests and patient management

A haematology sample was run in-house which revealed an increased red blood cell (RBC) count of 15.98 x10⁹ g/dl (RI 5–10 x10⁹ g/dl), HCT 55.6% (RI 24–45%) and increased platelets 1170x10⁹ g/dl (RI 300–800 x10⁹ g/dl); the remaining results were unremarkable. The haematology sample was run on the VetScan HM5 haematology machine in-house (Abaxis, Yorkshire). Manual PCV was 80% and total solids (TS) were 8 g/dl. The discrepancy between these values could have been a result of the blood viscosity hence a manual PCV must always be checked in these cases. The normal PCV in cats is 22–45% and TS is 6.0–7.5 g/dl (Orpet and Welsh, 2011). Full biochemistry and electrolytes were within normal limits, and coagulation profile was unremarkable, as was diagnostic imaging (chest radiographs, abdominal ultrasound, echocardiogram).

Therapeutic phlebotomy was performed to assist with the stabilisation of this patient. The patient was sedated for the procedure and the sedative agents of choice should have minimal cardiovascular depression as well as not making the therapeutic phlebotomy more challenging. Therefore a combination of butorphanol (0.4 mg/kg), midazolam (0.2 mg/kg) and alfaxalone (3 mg/kg) was chosen and all were given intramuscularly. Due to patient temperament and neurological signs, the cat was sedated with an intramuscular injection before intravenous catheter placement to minimise stress. A seizure ‘tray’ with diazepam ampoules, syringes, and needles, as well as the dose required were readily accessible in case of prolonged tonic clonic seizure activity.

The initial phlebotomy draw was 70 ml of blood. A 3 ml/kg fluid bolus of Hartmann's solution was given over 20 minutes immediately and the patient was maintained on 2 ml/kg fluid therapy overnight to support perfusion and hydration status.

During the phlebotomy procedure, the site (jugular and medial saphenous) was clipped and surgically prepped with dilute chlorhexidine and surgical spirit. A 23 g needle with butterfly catheter was used here to allow for prolonged blood draw from the jugular vein (Figure 2). Multiple sites were unfortunately required for vene-puncture in this patient. Therefore, appropriate after-care such as arnica cream and bandaging were used to maintain the patient's vascular access and reduce haematoma formation and pain.

Withdrawal of large volumes of blood from patients puts them at risk of inducing a state of hypovolaemia. This emphasises the importance of calculating the volume to draw before starting the procedure. Circulating blood volume that is reduced by 30–40% will cause hypovolaemia, which is detrimental to a patient's perfusion status (Magdesian, 2008). The PCV was 62% the following morning, and the TS 5.8 g/dl. There was a significant improvement in the patient's demeanour and clinical signs despite persistence of moderately increased PCV.

Management

Due to unremarkable diagnostic imaging, the patient was diagnosed with primary polycythaemia (polycythaemia vera) (Figure 3). The primary goal for this patient was to normalise blood viscosity by reducing the severely increased PCV. In this case, the acute management process started with numerous phlebotomy procedures to decrease RBC mass, subsequently diluting circulating RBCs, followed by monitoring for improvement of neurological presenting signs. The end goal of therapy was for the patient to maintain a PCV below 50% and sustained improvement in clinical signs. Usually, 10–20 ml/kg is the suggested amount for a safe blood draw from these patients and, in this case, roughly 20 ml/kg was taken. Formulae are available (McDonnell, 2012) to calculate exact amounts of blood to withdraw, however 10–20 ml/kg seems to be easier to use in practice and is effective.

Medication

The long-term management of polycythaemia vera often requires the use of hydroxyurea. This drug reduces haemopoeitic stem-cell replication, thereby inhibiting the rapid multiplication of RBCs which causes the extreme increase in RBC mass seen in polycythaemia vera. This chemotherapy is commonly used in the treatment of polycythaemia in dogs, cats and humans. This medication is used to reduce or abolish the need for repeated phlebotomies and the risks and welfare implications associated with the latter. Risks of repeated phlebotomy include repeated sedations, generalised weakness and thrombosis (Moore and Stepien, 2001).

Education

In terms of owner education and compliance, hydroxyurea is a medication that can be given at home while wearing gloves. However, owner health should be taken into consideration when the patient is prescribed a chemotherapy drug, and drug exposure should be avoided. Appropriate personal protective equipment is imperative for owners administering this medication (Frimberger and Moore, n.d). It is also important to consider that, as with all medications, some side effects may be observed. Common side effects of this medication are gastrointestinal and include vomiting and diarrhoea, as well as bone marrow suppression (Figure 4).

Discussion

Polycythaemia vera is uncommonly seen in small animal veterinary practices, unlike relative polycythaemia which is caused by fluid shifting and redistribution of RBCs in circulation (Table 1). A common cause of relative polycythaemia vera is dehydration and splenic contractions.

Absolute polycythaemia is the result of an actual increase in RBC mass. Absolute polycythaemia can be divided into primary and secondary causes (Table 1). Primary, otherwise known as polycythaemia vera, is a myeloproliferative disorder of the bone marrow, which results in increased RBC production independent of erythropoietin (EPO) levels caused by an unregulated production of the erythroid line. Secondary polycythaemia is considered EPO-dependent; EPO is synthesised in the kidney in response to hypoxia. Therefore, chronic hypoxia will stimulate an increase in RBC mass. Common diseases associated with secondary polycythaemia include: chronic lung disease, congenital heart defects, and renal cysts. However, it can also be caused by other hypoxic stimuli such as highaltitude environments. Excessive EPO production and release can also be caused by some primary tumours of the kidney and renal cysts.

After clinical discussion, it was decided by the internal medicine team to not measure blood EPO levels in this case. In relative polycythaemia, the results should be within the laboratory reference interval. In primary absolute polycythaemia (polycythaemia vera), it is expected that EPO concentrations are normal or decreased. In secondary absolute polycythaemia, EPO concentrations are expected to be increased (EPO-dependent disease). However, EPO concentrations in secondary absolute polycythaemia are often within the normal range; therefore, the utility of this test in differentiating the underlying cause of disease is low, which is why it was not performed in this case.

Polycythaemia vera has a relatively good prognosis. Long-term control of this condition is managed with repeated phlebotomy and hydroxyurea, as shown successfully in the case described in this article.

Role of the registered veterinary nurse

The present case was a good example of where registered veterinary nurses (RVNs) can be heavily involved with the patient from triage to discharge. Triage involves major body system assessment to determine which body systems are compromised and the degree of urgency of treatment that is required.

Primary survey

The primary survey included: heart rate, pulse rate and quality, respiratory rate and effort assessment, auscultation and a brief neurological examination. Neurological abnormalities as a result of blood viscosity are the most common presenting clinical sign seen during triage.

It is important to highlight that during the initial blood tests, there was a large discrepancy between the manual PCV and the reading from the haematology machine. It is often the role of the RVN to run these diagnostic samples; hence it is essential to be aware of inconsistent results displayed in practice as this could influence diagnosis and treatment. In addition to highlighting manual versus automatic PCV readings, PCV and TS must also be interpreted together along with clinical assessment findings. They provide information regarding the hydration status and red cell content of the patient (Table 2).

Therapeutic phlebotomy

In these cases, the RVN is normally heavily involved in the therapeutic phlebotomy procedures. This will involve discussion with the veterinary surgeon to devise a ‘safe’ anaesthesia plan to allow adequate blood draw from the patient. In this case, a sedation was deemed most appropriate to ensure cardiac protection, as well as a quick and efficient procedure with the fastest recovery. However, it can be argued that full general anaesthesia allows for maintenance of the patient's airway and continuous appropriate levels of anaesthesia for an adequate duration. The main factors considered in this case regarding the use of sedation versus general anaesthesia included: procedure type, patient temperament, health status and pharmacology of drugs considered. Similarly, the RVN often plays a major role in the blood draw and must therefore be confident in jugular and peripheral blood sampling.

The initial phlebotomy in this case was part of the initial patient stabilisation and it was necessary for it to be completed as early as possible for improved patient recovery. However, a consideration to improve the nursing care of these patients for future could be the placement of central jugular catheters or a peripherally inserted central catheter (PICC) with assessment risk of thrombus formation. It was not appropriate in the case of this feline patient because of her temperament, which would have been difficult to manage. However, if multiple phlebotomies were required in a short time frame, placement of a ‘long-stay’ catheter may have been beneficial as it reduces the need for multiple sedation protocols, decreasing risk to the patient; these catheters require adherence to strict aseptic protocols as the patient will be at risk of site infection.

Conscious phlebotomy

Conscious phlebotomy was not an option in this particular case; however, it is possible. In these cases, multiple sites can be clipped and 5% prilocaine and lidocaine topical cream (EMLA) can be applied and bandaged for 40 minutes prior to commencing. This topical local anaesthetic cream will make the procedure more comfortable for the patient but is not indicated in the emergency setting.

Another method of conscious phlebotomy for cases of polycythaemia vera is to use medical leeches to suck blood from the patient. This technique involves clipping an area of skin such as over the flank, warming the skin with warm water and pricking the skin using a scalpel to encourage leech attachment. It is common that bleeding continues from the skin for a further 24 hours after leeching because of the local anticoagulant injected into the skin by the leech. Therefore, this technique is an effective method to reduce PCV for a longer period of time than just that during which the leech is attached, and PCV and TS can be measured when spontaneous bleeding has discontinued. This technique is less invasive than multiple vene-puncture and is also safer to the major body systems. One leech sucks approximately 10 ml of blood before dropping off and the blood continues to ooze some time afterwards. Therefore, approximately only six leeches would be required for a patient of this size and PCV (Arnold and Glaus, 2001). This technique was not implemented in the current case, but is a consideration for future patients, although not all patients tolerate this procedure.

Neurological examination

As previously discussed, this case presented with neurological deficits and one suspected seizure episode. As part of the nursing care of this patient, it is essential to perform neurological examinations to observe for signs of deterioration or improvement. The modified Glasgow Coma Scale (GCS) is a useful guide for neurological assessment and is commonly used in canine patients to predict outcome of dogs with head trauma (Platt and Radaelli, 2001; Jevon, 2008). It is recommended that regular coma scales are completed for future cases of polycythaemia vera in cats presenting with severe neurological signs to aid observation and assess efficacy of the treatment plan. For example, a comparison in scores prior to initial therapeutic phlebotomy and 24 hours later will facilitate comparisons in the patient's health status and recovery. The reduction in PCV and perhaps an improvement in neurological evaluation are good prognostic indicators that initial therapy has been successful.

Patient follow-up

While RVNs are heavily involved with the inpatient's hospital care, their role does not end there. RVNs may assist the veterinary surgeon in client education; for example, how best to medicate their cat, maintain diet and continue to observe behavioural changes at home. Furthermore, often the RVN will conduct the follow-up haematology blood tests, and repeated phlebotomy procedures when necessary. However, if repeated phlebotomy is required despite hydroxyurea but is not achievable as a result of behavioural issues, alternative therapies such as medical leeches may be considered.

Conclusion

This case report discussed the successful diagnosis, treatment and management of a feline patient with polycythaemia vera in a referral hospital. These patients require repeated hospital visits for routine haematology blood samples and potentially further phlebotomy procedures if they cannot be solely managed with medication.

In this case, repeated complete blood counts were taken at regular intervals (3 months) with a manual PCV and TS measurement. These cases present rarely to veterinary practice, and with the challenging initial neurological assessment and numerous diagnostic tests required, some practices may see this as a challenge. The outcome of these patients will depend on the initial work-up including any underlying diseases, the temperament of the patient and client financial constraints. In this case, the patient made a good recovery and is doing well at home on medication with routine blood tests for monitoring (Figure 5).

KEY POINTS

• Polycythaemia vera is a relatively rare condition in cats presented to veterinary practice.
• There are several causes of polycythaemia and it is essential to differentiate between these causes for accurate diagnosis and treatment accordingly.
• Initial treatment is aimed at reduction of red cell mass via phlebotomy for prompt stabilisation in these patients.
• In cases where the phlebotomy has been successful to reduce circulating red blood cells these patients can be later managed at home on medication with close monitoring and repeated blood tests (primarily haematological analysis).