Diffuse Iris Melanoma in a Cat

Abstract

Background: Diffuse iris melanoma is rare, although is the most common primary intraocular neoplasm in cats, and is an unusual variant of anterior uveal melanoma. This neoplasm is malignant with high potential methastazed. Affects olders cats without breed or sex predisposition. The diagnosis can be made with fine needle aspiration cytology of anterior segment. The treatment is variable and depends of clinical signs evolution. The enucleation is commonly indicated when ocurred iridal pigment changes demonstrated as progressively increasing in size or number, or intractables uveitis or glaucoma. This work has for objectives to report a case of diffuse iris melanoma in a cat. Based on information available in the literature, this is the first case of diffuse iris melanoma in a cat documented in Brazil. Materials, Methods & Results: A ten-year-old, female, domestic shorthaired cat was examined for slowly progressive hyperpigmentation of the left eye enlarging over a 1-year period. The left iris was diffusely pigmented and irregular. The pupillary light reflex and menace responses were positives in the left eye. Physical examination was normal. As complementary exams had been realized complete blood cell count and serum chemical profiles, that were unremarkable. The thoracic, abdominal, and skull radiography did not show any evidence of metastasis. The treatment was the surgically removed of the left eye. The histopathological evaluation confirmed the tumor as a malignant melanoma with diffuse involvement of the iris stroma. Two years after enucleation, the cat was clinically normal, and thoracic and abdominal radiography did not show any evidence of metastasis. Discussion: The diffuse iris melanoma affects, mainly, cats than more nine years old. It typically presents as focal to diffuse iris hyperpigmentation rather than a discrete nodule or mass. In this cat, the clinical features and biological behavior were similar to other previous reports. The neoplasm has character infiltrate may lead to development of uveitis, glaucoma and metastasis in organs such as regional lymph nodes, lungs and liver. Pupillary deficits and buphtalmia may also be associated. In this case, no clinical signs other than the iris hyperpigmentation and irregularity of the iris surface was observed against of the complementary exams. The main differential diagnosis must be made of benign forms of iris hyperpigmentation secundary to chronic uveitis and iris melanosis. The diagnosis through of the fine needle aspiration cytology of anterior segment was considered, but not performed due to potential intraocular complications. The treatment of choice may depend on the tumor growth rate and the age of the patient, may be appropriate only to observe the tumor. The enucleation was indicated due to the extensive neoplastic invasion of the iris. Moreover, considering the metastic rate of diffuse iris melanoma in cats and a long latency period of metastic disease, the early enucleation, has been proposed by literature. After remotion of the affected eye definitive diagnosis was obtained by histophatology. The examination revealed pleomorphic spindle cells irregularly pigmented showing sometimes heavy pigmented round neoplastic cells “plump cells” and other slightly pigmented with increased mitotic figures compatible with diffuse iris melanoma. The prognosis of feline anterior uveal melanoma is poor with a high risk of metastatic diseases and a shortened life. The patient no evidenced metastasis and recurrence after two years, illustrating the importance of early diagnosis and treatment in order to avoid premature death.