Melanocytic tumor is common in dogs and is mostly malignant¹. Melanomas in dogs are most frequently found in buccal cavity², the haired skin, nail bed, footpad, eyes, gastro-intestinal tract, central nervous system and muco-cutaneous junctions³. Melanoma is a tumor of older dogs without sex predilection, but some breeds are at high risk to develop melanoma as the genetic predisposition is an underlying etiological factor, which varies among breeds⁴. Digital forms seem to have intermediate prognosis with a median survival time of 11.8 months⁵. This present report deals a recurrent case of malignant melanoma in a Doberman pinscher dog.

A ten year old male Doberman pinscher dog was presented to the Veterinary Clinical Complex, Veterinary College and Research Institute, Namakkal with the history of lameness and progressive growth at the ventral aspect of the right forelimb. Detailed clinical examination was carried out. Blood and serum samples were collected for routine haemogram and serum biochemistry, respectively. Cytological smears were collected from the growth by Fine needle aspiration cytology (FNAC) and were stained with Giemsa and Leishman stain. Based on the clinical picture, haemogram and cytology, it was decided to remove the mass. The tissue pieces from various masses were fixed in 10% formalin for histopathological examination. The tissue samples were processed by paraffin embedding technique and 4μ. thick tissue sections were stained with routine haematoxylin and eosin⁶.

Clinically the animal exhibited lameness with normal temperature, pulse and respiration rate. There were multiple black coloured circular masses noticed at the palmar aspect of right forelimb. The haemogram and serum profile were almost normal (Hb-16 g/dl, PCV- 49%, RBC- 8.13 * 10⁶/cumm, WBC - 9.14* 10³/ cumm, total protein 5.92 g/dl and albumin - 2.81 g/dl).

On physical examination, there were multiple small (1 cm) to medium (6 cm) sized brown to black raised and wrinkled growths noticed at the palmar aspect of the right forelimb (Fig. 1). Some ulcerated growths with superficial haemorrhage were also noticed. The FNAB samples exhibited sheets of round cells with anisokaryosis, poikilokaryosis, prominent multiple nucleoli and intracytoplasmic black coloured pigments (Fig. 2).

The surgery was performed under premedication with atropine sulphate @ 0.04 mg/ kg body weight subcutaneously and xylazine hydrochloride @ 1.0 mg/kg body weight intramuscularly. General anesthesia was induced with ketamine hydrochloride @ 5.0 mg/kg body weight and diazepam 0.5mg/ kg body weight intravenously and maintained with isoflurone 2.5%. Tumor masses were excised at the base level after ligating the blood vessels lying on the palmar aspect of right forelimb with catgut No.1. Post operatively, the animal was administered with Ceftriaxone @ 10.0 mg /kg body weight, intravenous injection of normal saline 10 mg /kg body weight, Meloxicam @ 0.50 mg/kg and Ranitidine 0.5 mg/kg body weight, subcutaneously for three days. But recurrence of tumour masses was noticed within two months of surgical removal, which indicated the malignant type of neoplasm.

Histopathologically, the tissue section from the masses revealed the presence of clusters of melanin laden melanocytes in the dermis (Fig. 3) and even to the level of hypodermis. The proliferating neoplastic cells appeared as solid clusters, cellular sheets and parallel cords. The tumour cells were round to ovoid in shape and variable in size with hyperchromatic nuclei. The nuclei of tumour cells also exhibited polymorphism, anisokayrosis with prominent and multiple nucleoli. The cytoplasm of the neoplastic cells had dark brown to black coloured melanin pigment. The mitotic index was higher (24/ ten high power field) and occasional multinucleated tumour giant cells were also observed. Similar microscopic observations also made by earlier author⁷

The causes of melanomas are uncertain. In humans, risk factors such as race, lack of skin pigmentation, excessive exposure to sunlight and the presence of preexisting nevi have been described⁸. Though melanoma is common in animals with grey or white hair coats, dark-skinned animals also more often affected⁹. In the present study also, malignant melanoma has been noticed in dark skinned animal.

In conclusion, this case is a recurrent type of malignant melanoma in a dog with aggressive nature, which is well evidenced by the microscopic picture of tumour masses viz. pleomorphism, cytoplasmic pigmentation, giant cells and high mitotic figures.

The authors are thankful to Tamil Nadu Veterinary and Animal Sciences University for providing the facilities.

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