Equine melanoma shows striking features particularly with regard to clinical development in grey horses: in contrast to malignant melanoma in humans and in solid coloured horses that are characterized by early onset of metastasis, pigment cell tumours display almost benign clinical features in ageing grey horses. Through evolution, grey horses appear to be in a favourable position in regard to the biological behaviour of melanomas. Yet unknown factors inhibiting or retarding early melanoma metastasis may be responsible for this phenomenon. In this study, immunostaining profiles and histopathologic patterns of equine vs. human melanotic tumours were compared. In addition, the expression of melanoma markers currently used in human melanoma detection and characterization were evaluated for their applicability in equine melanoma diagnosis. Immunohistopathologic investigations revealed that benign grey horse melanomas share common features with human blue nevi and with human malignant desmoplastic melanomas, whereas their resemblance to other types of human cutaneous malignant melanomas is less pronounced. Our data equally underline that S-100, proliferating cell nuclear antigen (PCNA), HMB-45, Ki-67, T-311 and CD44 can serve as reliable markers for horse melanomas. Further investigations aiming at identifying factors retarding metastasis in affected grey horses are needed, as they may contribute to the development of novel treatment strategies for human malignant melanoma.

Haematogenous osteomyelitis is a rare form of bone infection in adult dogs. Most commonly the infection is iatrogenic or traumatic in origin. The authors report three different presentations of haematogenous osteomyelitis: a focal pelvic localisation in a growing dog, a vertebral lesion in an adult dog with associated neurological signs and a multifocal affection in another adult dog with concomitant pathological fractures. Clinical signs included pyrexia of undetermined origin, focal pain and lameness. Diagnostic investigation included radiographic imaging, bone scintigraphy, magnetic resonance imaging, surgical biopsy, and bacteriological culture with sensitivity testing of biopsy specimens as well as of peripheral blood samples. Treatment consisted of long-term antimicrobial therapy and surgical debridement with curettage of the pelvic abscess of the young dog and decompressive hemilaminectomy of the second dog, with excellent recovery. The dog affected by polyostotic bone involvement and suffering pathological fractures was euthanatized. Haematogenous osteomyelitis may be a diagnostic and therapeutic challenge and may present as a devastating skeletal condition, even in adult dogs, and should be considered amongst the differential diagnoses early on to allow effective treatment.

Antibodies to homologous collagens, types I and 11, have been found in the sera and synovial fluids of dogs with spontaneous cruciate ligament rupture and osteoarthritis. Samples from 30 dogs with degenerative joint disease of the knee and from 15 healthy dogs were investigated by enzyme-linked immunosorbent assay. Fifty-three percent of dogs with joint disease showed significant levels of anti-type I collagen antibodies in their sera, and 56% had anti-type I1 reactivity. Ninetyone percent of the dogs with joint disease exhibited antibody reactivity to type I collagen in their synovial fluid, and 88% showed reactivity to type I1 collagen. Correlation of these results with the clinical data indicated that the antibodies had been elicited by antigens derived from cruciate ligaments (type I collagen) and from altered joint cartilage (type I1 collagen). Immunologic reactivity in this form of canine osteoarthritis is a new concept, and it should be considered in our attempts to understand the pathogenesis of this disease.

Perineal hernia occurs spontaneously in older male dogs after idiopathic weakening of the pelvic diaphragm. Hernias invariably contain cystic paraprostatic tissues. Castration reduces incidence and recurrence after surgical repair. Although cystic prostatic hypertrophy is a consistent feature in patients with perineal hernia, an endocrine link of the disease to steroid sex hormones has not been demonstrated. Employing immunohistochemistry, we found intense relaxin immunoreactivity in dogs with perineal hernia within the epithelia of hypertrophic prostates and in periprostatic tissues. The prostate of normal dogs exhibited similar but less intense relaxin staining. In neutered dogs with prostatic atrophy, relaxin immunostaining was weak or absent. Periprostatic cysts highly expressed relaxin precursors in the fluid phase as shown by SDS-gel electrophoresis. Relaxin of prostatic origin, therefore, is possibly a local factor in connective tissue weakening and subsequently in perineal hernia formation.