Diagnosis and treatment of concurrent dermal malignant melanoma and melanocytomas in a pygmy hippopotamus (Choeropsis liberiensis).

Background: Dermal melanocytic neoplasms are common in some even-toed ungulates (Artiodactyla), yet this entity has not been reported in the pygmy hippopotamus to date. Concurrent occurrence of multiple benign and malignant melanocytic neoplasms is unusual. Malignant transformation occurs in a small percentage of benign melanocytic tumours in people but this phenomenon has not been well documented in animals.

Objectives: To report the diagnosis and treatment of concurrent dermal melanocytomas and malignant melanomas in a pygmy hippopotamus.

Animals: A 36-year-old intact male pygmy hippopotamus, part of a zoological collection, housed with a 10-year-old female of the same species, presented with multiple raised and pigmented skin masses.

Methods: Initial impression smears of one ulcerated lesion were consistent with inflammation; subsequent histopathological findings from a skin biopsy revealed an underlying malignant melanoma. The animal was anaesthetised, ultrasonographic imaging of the local lymph nodes indicated no local involvement and all skin lesions were removed. Recovery from anaesthesia was unremarkable, skin healing was within normal limits for the species. There was no sign of recurrence 34 months post-surgery.

Results: A diagnosis of malignant melanomas and concurrent melanocytomas was made on histopathological evaluation.

Conclusion And Clinical Importance: To the best of the authors' knowledge, this is the first reported case of melanocytic neoplasia in the pygmy hippopotamus. The occurrence of both benign and malignant melanocytic skin tumours should be considered in this species.