ISVD Abstracts


Amelanotic balloon cell melanoma: a diagnostic challenge


An Independent Biopsy Service, Venice, California, USA

Nonpigmented cutaneous or subcutaneous neoplasms with balloon cell morphology are rare and present a diagnostic dilemma. A survey of all accessions at this laboratory from 1997 to 1999 yielded nine neoplasms that had been assigned a preliminary diagnosis of malignant balloon cell tumour. The cases comprised eight dogs and one cat ranging from 1 to 12 years of age. All lesions were solitary, and there was no site predilection. There has been no known recurrence or metastasis since time of diagnosis in seven of the cases, with follow-up intervals ranging from 3 to 32 months (one dog died of unrelated causes, and another was lost to follow-up). Balloon cell morphology is characterized by round to polygonal cellular profiles and pale or clear cytoplasm that is finely vacuolated, reticulated or granular. Definitive determination of cell type is usually not possible from routinely stained sections. For balloon cell neoplasms with obvious features of malignancy, differential diagnoses include melanoma, sebaceous carcinoma, anaplastic mast cell tumour, malignant granular cell schwannoma and liposarcoma. Fontana-Masson stain for melanin is a very helpful adjunctive test, yielding positive results in three of the seven cases in which it was performed. Positive immunostaining for S100A, a major subgroup of the S100 class of proteins that has increased specificity for melanocytes, also provides confirmation of a diagnosis of amelanotic balloon cell melanoma.


A case of autoimmune vasculitis affecting ears and nose in a cat with panleukopenia enteritis


Departamento de Patología, Escuela de Medicina Veterinaria, Universidad Nacional, Heredia, Costa Rica

A 3-month-old, male mixed breed cat was presented with a clinical history of inappetence, sneezing, mucopurulent nasal discharge and pale mucous membranes. The cat was treated with intramuscular enrofloxacin and intravenous fluid therapy. A complete blood count revealed anaemia (haemoglobin 4.5 g dL−1, haematocrit 18%, CHMC 25%) and leukopenia (leukocytes 600 uL−1, segmented neutrophils 40% bands 5%, lymphocytes 52%, monocytes 3%). On the next day, erosions and crusts were noted on both the pinnae and dorsal aspect of the nose. On day 3, no new changes were observed. On day 4, the right carpal region was swollen and the mucous membranes appeared icteric. Antibiotic administration was discontinued. On day 5, there was no improvement. On day 6, the antibiotic and intravenous fluid therapies were administered again, as the cat became more icteric and lethargic. The cat was euthanazed the following day. Necropsy showed multiple erosive to ulcerative lesions with some crusting on the dorsal aspect of the nose, whereas the ears had more crusting and less ulcerative lesions. Microscopically, lesions on the ears and nose consisted of severe epidermal necrosis with marked acute vasculitis. The small intestine showed histological lesions consistent with panleukopenia.


Canine alopecia areata: clinical, pathological, and immunological observations (24 cases)


College of Veterinary Medicine, North Carolina State University, Raleigh, North Carolina, USA; University of Bradford, Bradford, West Yorkshire, UK

In various mammalian species, alopecia areata (AA) is an autoimmune disease directed against hair bulbs. The purpose of this study is to report the clinical and immunopathological data collated from 24 dogs with AA. Clinical symptoms usually arose during adulthood (median: 5 years). Alopecia (92% of dogs) and leukotrichia (9%) were the lesions first seen on the face (71%), forehead (25%) or ears (13%). Full-blown lesions consisted of alopecia (100%), skin hyperpigmentation (46%) and leukotrichia (27%). These lesions were distributed on the face (71%), forehead (38%), ears (26%) or legs (26%). Facial alopecic patches commonly exhibited bilateral symmetry (80%). Spontaneous remission of alopecia was seen in 11/18 dogs (61%). Regrown hair shafts often were unpigmented (67%). Histological examination of skin biopsy specimens revealed bulbitis (62% of hair bulbs) and peribulbitis (45% of hair bulbs) affecting almost exclusively anagen hair follicles (HF). In 25% of dogs, dystrophic hair shafts were seen. Direct immunofluorescence testing revealed HF-specific IgG antibodies in 11/15 dogs (73%). In 10/15 patients (67%), these antibodies bound to the glassy membrane of the inferior HF. Indirect immunofluorescence demonstrated circulating anti-HF IgG autoantibodies in 12/12 sera. Immunoblotting, performed with human anagen HF extracts, established that IgG autoantibodies from 12/12 dogs recognized multiple HF proteins including 200–220 kDa trichohyalin and 45–60 kDa hair keratins. These observations are very similar to those collected from human patients with AA. Canine AA could be used therefore as a suitable model to study the pathogenesis of this common autoimmune disease of humans.


Nodular cutaneous dirofilariasis in a cat


Dermatopathology Services, Woodland, California, USA

A 4-year-old, domestic shorthaired cat was presented for multiple cutaneous nodules located on the dorsal midline of the head at the nuchal crest, and on the left side of the chest at the tenth intercostal space. No other abnormal clinical finding were observed. The cutaneous nodules had been present for approximately 1 year, with no noticeable change in size during that time. Both nodules were surgically excised en bloc. Histologically, one of the nodules contained viable male and female filarid nematode parasites morphologically compatible with a Dirofilaria species. The other remaining nodule contained many dead filarid nematode parasites. Serum antigen and antibody testing for Dirofilaria immitis was positive. Diagnostic testing of this individual for signs of heartworm disease, and change in serum antigen and antibody levels continues. Adult worms of D. immitis causing nodular cutaneous lesions are reported occasionally in dogs, and rarely in cats.


Focal pyogranulomatous dermatitis associated with colonization of epidermal keratin by Ulocladium, a dematiaceous fungus


College of Veterinary Medicine, University of Illinois, Urbana, Illinois; Scientific Laboratory Division, New Mexico Department of Health, Albuquerque, New Mexico, USA

A 7-year-old neutered male brown mixed breed dog (Labrador retriever and Weimaraner cross) was presented for a moist, mainly interdigital pododermatitis of the left fore foot with hair loss of 6 months’ duration. The condition had been temporarily responsive to oral antibiotics, and waxed and waned despite treatment with various antibiotics and a short course of corticosteroids. Subsequently, a crusty alopecic plaque on the side of the muzzle developed. Biopsy of both sites on two occasions revealed a lichenoid to perivascular, nonsuppurative to pyogranulomatous dermatitis with locally extensive loss of follicles and small to moderate numbers of fungal elements in the keratin layers of the epidermis and of a follicular ostium. Fungi were septate with parallel walls; culture of the lesion yielded a pure growth of Ulocladium, a dematiaceous fungus usually thought of as a saprophyte. The condition was responsive (except for hair loss) to a 3-week course of ketoconazole. This fungal infection may have been primary or secondary to a bacterial infection or to antibacterial or corticosteroid therapy. The dog’s environment (dirt yard with frequent visits to a sheep farm and swims in a local pond) may also have played a role in his skin infection.


Exfoliative dermatitis associated with thymoma in a Somali cat


Laboratories of Veterinary Diagnostic Medicine, University of Illinois, Urbana, Illinois; Pet Vet Animal Clinic, Huntley, Illinois, USA

An 11-year-old, female spayed Somali cat was presented with a 4–6-week history of alopecia and crusting dermatitis affecting the head and trunk. The cat was treated with enrofloxacin, prednisone, ivermectin, and chlorhexidine shampoo with little improvement. Over the next 2 weeks, the cat developed progressive anorexia and weakness and was subsequently euthanazed. Findings at necropsy included alopecia, crusting dermatitis, bronchopneumonia, and a mediastinal mass. Histopathology revealed hyperkeratotic interface dermatitis with individually necrotic keratinocytes present in the stratum basale and stratum spinosum. The mediastinal mass was histologically consistent with a thymoma. Lung changes included a necrosuppurative bronchitis and bronchiolitis, consistent with acute aspiration pneumonia. Differential diagnoses for the histological skin changes included erythema multiforme, acute systemic lupus erythematosus, thymoma-associated dermatitis, and graft-vs.-host-disease. Thymomas in cats have been associated with several paraneoplastic syndromes presumptively caused by dysfunctions of the immune system, including various dermatoses, myasthenia gravis, myocarditis, and polymyositis. The clinical signs and findings in this case are compatible with this syndrome.


A proliferative thrombovascular necrosis in both pinnae of a Dalmatian dog


Departamento de Patología, Escuela de Medicina Veterinaria, Universidad Nacional, Heredia, Costa Rica

A 1.6-year-old, male Dalmatian dog was presented for evaluation of lesions on the margins of the apex of both ears. The owner reported that lesions had been present in the left ear for 1 year and in the right for 6 months. Prior treatment did not alleviate the condition and consisted of topical antiseptic solutions. Upon examination, the left ear pinna showed ulceration, bleeding and crusting, with the lesion extending to the internal pinna. The right ear had similar lesions but they were not as moist and active. A skin biopsy was performed and histological examination showed that the epidermis exhibited acanthosis, orthokeratotic and parakeratotic hyperkeratosis, and hyperpigmentation. The dermis was filled with proliferative vascular structures separated by stromal tissue. The luminal vessels contained erythrocytes and fibrin like material. Based on clinical presentation and dermatopathological changes, the diagnosis of proliferative thrombovascular necrosis was made.


Malignant dermal melanoma in a horse with unusual histopathologic appearance and cytokeratin reactivity


Livestock Disease Diagnostic Center, Department of Veterinary Science, University of Kentucky, Lexington, Kentucky; Department of Pathobiology, College of Veterinary Medicine, University of Florida, Gainesville, Florida, USA

Dermal melanocytic tumors are common in old grey horses and are usually benign. Malignant melanocytic tumors are rare in horses, do not have an association with grey coat colour, and can metastasize widely. A mass was excised from the skin of the back of a 13-year-old bay Thoroughbred mare. The poorly demarcated mass was comprised of cords and clusters of round to cuboidal tumor cells. Tumor cells were supported by a moderately abundant collagenous stroma containing scattered foci of myxoid matrix. Moderate numbers of tumor cells contained small amounts of Fontana-positive cytoplasmic pigment. Nuclei were round to C-shaped, with finely granular chromatin and one to several small nucleoli. There was moderate anisokaryosis, and 0–2 mitotic figures were observed per 400× field. Tumor cells were infiltrative at lateral and deep margins. Immunohistochemically, there was diffuse, positive cytoplasmic staining of tumor cells for S-100, neurone-specific enolase, and vimentin. Some clusters of tumor cells also stained positively for pan keratin. Tumor cells in this case showed features intermediate between previously described dermal melanomas and anaplastic malignant melanomas in horses. Nuclear morphology was not typical of a melanocytic tumor, nor was the presence of myxoid matrix within the stroma. Staining of melanocytic tumor cells for cytokeratin has been reported previously in human patients and typically involves less than 10% of tumor cells. Immunohistochemical staining for melanocytic markers is important in the diagnosis of poorly differentiated cutaneous tumors in horses. To the authors’ knowledge, cytokeratin positivity has not previously been documented in equine melanocytic tumors.