A histopathological and immunohistochemical study of cutaneous nodular lesions and other surface swellings of Kenyan horses

Abstract

The objective of the study was to determine the trends of nodular cutaneous lesions and other surface swellings of the horse in Kenya and to relate the histological and immunohistochemical characteristics to the clinical parameters. The study used the retrospective and prospective cases presented to the Department of Veterinary Pathology, Microbiology and Parasitology, University of Nairobi for histological diagnosis and from which a diagnosis of cutaneous pathology was recorded. The procedure involved retrieval of diagnostic reports from retrospective cases and histopathological examination of both retrospective and prospective cases. Each case was evaluated for the type and frequency of histological lesions and clinical data. Parameters included analyses of age, sex, breed, geographical origin, diagnosis, location of neoplasms, the pathology of the lesion, and the clinical features presented. The histological features were compared between cases and cellular behaviour was correlated with clinical parameters. Immunohistochemistry was performed on morphologically related lesions. A total of 141 cases were identified for the study at the Department, between 1967 and 2014. Neoplastic lesions accounted for 64.5% (91/141) while inflammatory lesions accounted for 31.9% (45/141). The most common neoplastic lesion was squamous cell carcinoma (35.2% - 32/91), followed by the equine sarcoid (20.9% - 19/91), melanocytic neoplasms (18.7% -

17/91) and fibroblastic neoplasms (14.3% - 13/91). The most common inflammatory lesion was granuloma (46.7% - 21/45), most of which were granulomas exhibiting the presence of numerous eosinophils, due to a likely parasitic aetiology. There were two cystic cases, an epidermoid cyst and a dermoid cyst. Two different biopsies submitted from a 3 year old male were associated with cutaneous lesions caused by Besnoitia spp. Other granulomas exhibited histological characteristics similar to those of a fibroblastic neoplasm. A few cases of “proud flesh” were also encountered. Immunohistochemistry was performed according to the manufacturer’s (Dako®) protocol and it resulted in adequate staining of the antigen on selected cases. The histological diagnosis was confirmed in most instances (90% - 18/20). Discrepancies were encountered between the histopathological diagnosis and the results of immunohistochemistry in 10% (2/20) of the cases. This study is the first to document the cutaneous lesions and other surface swellings of horses in Kenya, describing the histological and immunohistochemical characteristics. The study has also established that commercially available standardized immunohistochemical kits for various antigens can be used effortlessly to help distinguish between various morphologically related lesions. The results form the basis for further studies on the application of immunohistochemistry in routine veterinary diagnostics in Kenya. Key words: Equine, Horse, Cutaneous, Neoplastic, Non-neoplastic, Equine sarcoid, Squamous cell carcinoma, Granuloma, Besnoitia spp., Histopathology, Immunohistochemistry