Multiple canine mast cell tumours

48 Multiple canine mast cell tumours




INITIAL PRESENTATION


Multiple cutaneous nodules in a Weimaraner.



INTRODUCTION


Mast cell tumours are the most common canine cutaneous neoplasm. They are challenging tumours to deal with in a clinical situation, because of their variable clinical appearance, variable behaviour and potential for malignancy. This report describes a case of multiple mast cell tumours in a Weimaraner.




CASE PRESENTING SIGNS


A 6-year-old, spayed female Weimaraner was presented with multiple cutaneous nodules.



CASE HISTORY


The history in cases of mast cell tumour (MCT) is variable. Tumours may have developed recently, or can have been present for months or even years and then suddenly start to behave in a malignant manner. Mast cell tumours are variably pruritic. There may be a history of sudden increases and decreases in tumour size over a period of hours to days. Alternatively, some dogs with MCT have a history of repeated episodes of erythema and urticaria or angioedema (‘Dariers sign’). Both these scenarios are the result of a massive release of vasoactive mediators from the mast cells. Systemic signs, including vomiting, delayed wound healing and coagulopathies, may be evident.


This dog presented with the following history:


• A 12-month history of intermittent episodes of widespread urticaria, and angioedema involving the pinnae and eyelids.

• A 5-month history of multiple dermal nodules. According to the owner, some nodules appeared to be spontaneously resolving whilst others were increasing and decreasing in size.

• Over the past 3 months there had been a more rapid increase in the number of nodules and some lesions had ulcerated.

• Some of the nodular lesions had been mildly pruritic.

• Apart from occasional vomiting, there were no other signs suggestive of systemic involvement.

• There was no zoonosis.

• Recent treatment had consisted of chlorphenamine at a dosage of 0.4  mg/kg b.i.d. to treat any episodes of urticaria or angioedema, and systemic antibacterial therapy to treat secondary infection of ulcerated lesions. The use of chlorphenamine had, to a large extent, prevented the urticarial episodes.


CLINICAL EXAMINATION


Mast cell tumours most commonly present as raised or ulcerated cutaneous masses. They may be haired or hairless, single or multiple, dermal or subcutaneous. MCTs are often reported to resemble lipomas, but they can look and feel like many different skin diseases. They are seen most commonly on the skin of the trunk and hindquarters, and on the extremities. In most cases MCTs are solitary lesions, but around 10% of dogs present with multiple tumours.


In this case the findings were:


• A general physical examination was within normal limits.

• There were numerous subcutaneous nodules ranging from a few millimetres to 1–2  cm in diameter over the entire integument. Some of these nodules had an ulcerated surface, particularly those over the left hindlimb and one over the left pinna (Figs 48.1, 48.2 and 48.3).

image

Figure 48.1 Generalized subcutaneous nodules on the entire body.


image

Figure 48.2 Ulcerated nodules on a hind limb.


image

Figure 48.3 Close-up view of nodules on the left thigh.




DIFFERENTIAL DIAGNOSES


The differential diagnoses for multiple nodular lesions included:


• Neoplasia, including:
• Mast cell tumour

• Cutaneous lymphoma

• Lipoma

• Histiocytoma

• Sterile granulomatous/pyogranulomatous disease

• Bacterial or fungal granuloma.


CASE WORK-UP


The first step with any nodular disease is to perform fine-needle aspiration. Except in the case of poorly differentiated tumours, the diagnosis of MCTs is usually easily made on cytological examination of fine-needle aspirates. Diff Quik® or Rapi-Diff® are appropriate stains for cytological examination. Mast cells appear as small to medium-sized round cells, the nuclei are centrally placed within the cell, giving a ‘fried egg’ appearance, and the cytoplasm usually contains abundant dark staining granules (see Chapter 2). Eosinophils are frequently encountered. NB: Mast cell granules may be difficult to visualize in poorly differentiated MCTs.


The advantages of fine-needle aspiration over excisional biopsy are that it is inexpensive, it can be performed with the animal conscious and, in the case of mast cell tumour, is usually diagnostic. Additionally, an effective first surgery is most likely to result in a cure and prior fine-needle aspirates allow for effective surgical planning. The major limitation of fine-needle aspiration is that it is not possible to predict the behaviour of the tumour; histology is much more useful in this respect.



• Fine-needle aspirates were taken of several non-ulcerated nodules. Cytological examination of the aspirates showed large numbers of mast cells and occasional eosinophils (Fig. 48.4).

image

Figure 48.4 Mast cells with both intracellular and extracellular granules. Also shows an eosinophil (arrow).


The cytology was consistent with a diagnosis of mast cell tumour. All mast cell tumours have metastatic potential, and the next stage was to clinically stage the case and establish the likelihood of metastasis prior to deciding on a treatment strategy.


Staging the tumour: Traditionally, a range of tests have been used to try and establish the presence or absence of metastatic disease. The tests include analysis of buffy coat smears, bone marrow aspiration, splenic and hepatic ultrasound-guided biopsies, radiographs and ultrasonography. Recent evidence has shown that some of these tests are of low specificity or sensitivity. For example, buffy coat smears were only positive in 30% of dogs with poorly differentiated tumours and were positive in dogs with 85 other diseases. Lymph node aspirates are of value, but mast cells may be seen in aspirates from dogs that do not have MCTs. Note that mast cell tumours tend to metastasize diffusely to visceral organs, and thoracic radiography is usually negative for the classic ‘cannon-ball’ metastases.


Bearing in mind these limitations, the following tests were carried out:


• Routine haematological and biochemical examinations showed a moderate basophilia (0.2 × 109/l).

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Sep 3, 2016 | Posted by in SMALL ANIMAL | Comments Off on Multiple canine mast cell tumours

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