A review of cutaneous hypersensitivity reactions in dogs: A diagnostician's guide to allergy.

Allergic dermatoses are common in people and domestic animals. Resultant lesions are routinely biopsied and submitted for histological examination to confirm a diagnosis or rule out diseases with overlapping or atypical clinical features. Diagnostic pathologists and clinicians are often faced with the difficult task of determining whether an allergic reaction pattern is present on both the microscopic and macroscopic levels and correlating histopathologic findings with clinical and historical data to achieve a precise clinical diagnosis. The bulk of the current veterinary literature on allergic dermatoses focuses on atopic dermatitis in dogs, distantly followed by cats, horses, and other animals. The objectives of this review are to demonstrate the key histopathologic and clinical diagnostic features of the various allergy-mediated reaction patterns, and to provide diagnosticians with a practical guide for clinicopathological correlations. Current concepts in the pathophysiology of immediate hypersensitivity reactions, with a focus on atopic dermatitis, are discussed. Points of potential histopathologic overlap between the "classic" allergic reaction pattern and less common inflammatory, predominately eosinophilic, conditions that may mimic this pattern will be discussed with the goal of highlighting the critical need for collaboration between pathologists and clinicians in furthering patient care.

Clinical and histopathological features of rostrolateral nasal alar arteriopathy of German shepherd dogs.

BACKGROUND: Dermal arteritis of the nasal philtrum (DANP) has been described in large-breed dogs. OBJECTIVES: To characterise clinically distinct, discrete fissures of the dorsolateral nasal alae associated with severe bleeding in German shepherd dogs (GSDs). ANIMALS: Fourteen privately owned GSDs with linear rostrolateral nasal alar fissures and a histopathological diagnosis of nasal vasculopathy. MATERIALS AND METHODS: Retrospective analysis of medical records and histological slides. RESULTS: Mean age of onset was 6 years. Before biopsy, episodic arteriolar bleeding was noted in 11 of the 14 (79%) dogs. Slide analysis revealed enlarged nasal arterioles with expanded vascular tunics and luminal stenosis beneath ulcers. Histopathological lesions consistent with mucocutaneous pyoderma and/or facial discoid lupus erythematosus were present in 5 of the 14 (36%) dogs. Enlarged arterioles stained blue with Alcian blue and Masson's trichrome stains, consistent with deposition of mucin and collagen, respectively. Immunohistochemical stains (neutrophil myeloperoxidase, IBA1, CD3) were performed. CD3 was negative for all dogs, whilst neutrophil myeloperoxidase and IBA1 occasionally demonstrated intramural neutrophils (3 of the 14 dogs, 21%) or histiocytes (1 of the 14 dogs, 7%) in altered vessels, respectively. All dogs underwent medical management and/or surgical excision. Treatments included tacrolimus, prednisone, ciclosporin-modified, pentoxifylline, antimicrobials and doxycycline/niacinamide. No dogs were treated with antimicrobials alone. For seven dogs with long-term follow-up, treatment response was complete in five (71%) and partial in two (29%), with six of the seven (86%) receiving immunomodulatory treatments to maintain remission. CONCLUSION AND CLINICAL RELEVANCE: Nasal alar arteriopathy of GSDs shares histopathological changes with DANP. It has characteristic clinical and histopathological features and appears amenable to immunomodulation.

Cutaneous mastocytosis in 8 young dogs and review of literature.

Cutaneous mastocytosis (CM) is a rare condition in young dogs characterized by multicentric cutaneous proliferation of neoplastic mast cells. Clinical data from 8 dogs that met inclusion criteria (age of onset less than 1.5 years, greater than 3 lesions) were obtained via a standardized survey. Biopsy samples were classified by the Kiupel/Patnaik grading systems and analyzed for c-KIT mutations. The median age of onset was 6 months (range: 2-17 months). Dogs had 5 to more than 50 lesions characterized as nodules, plaques, and papules. Seven dogs were pruritic. Clinical staging in 2 dogs did not reveal visceral involvement. No dogs had systemic illnesses at diagnosis. Histologically, CM was similar to cutaneous mast cell tumor (cMCT). Two dogs had neoplasms classified as high-grade/grade II while 6 dogs had low-grade/grade II neoplasms. No dogs had mutations in c-KIT exons 8 and 11. Treatment included antihistamines (8/8), corticosteroids (7/8), lokivetmab (3/8), and toceranib (1/8). Six dogs were alive with lesions at the end of the study with a median follow-up time of 898 days, while 2 dogs were euthanized. In dogs with high-grade/grade II neoplasms, one continued to develop lesions at 1922 days post-diagnosis, while the other dog was euthanized at 56 days post-diagnosis. One dog was euthanized 621 days post-diagnosis due to rupture of a neoplasm. CM occurs in young dogs and is histologically indistinguishable from cMCT. Current histologic grading systems did not apply uniformly to the dogs of the study and further studies are needed.

A comparison study of microwave ablation vs. histotripsy for focal liver treatments in a swine model.

OBJECTIVE: To compare the acute and chronic safety and treatment effects of non-invasive hepatic histotripsy vs. percutaneous microwave (MW) ablation in a healthy porcine model. METHODS: This was a dual-arm study in which each animal (n = 14) received either a single hepatic microwave (n = 6) or histotripsy (n = 6 single treatment; n = 2 double treatment) under ultrasound guidance. The goal was to create 2.5-3.0 cm short-axis treatments in similar locations across modalities. Animals were survived for 1 month with contrast-enhanced CT imaging on days 0, 2, 7, 14, and 28. On day 28, necropsy and histopathology were performed. RESULTS: All procedures were well-tolerated. MW ablation zones were longer and more oblong, but equivalent in the short axes to histotripsy zones on immediate post-procedure CT (p < 0.001 and p = 0.45, respectively). Overall, MW volumes were larger (21.4 cm3 vs. 13.4 cm3; p = 0.001) and histotripsy treatment zones were more spherical (p = 0.007). Histotripsy zones were close to the prescribed size (p < 0.001). Over the study period, histotripsy treatment zones decreased in volume while microwave ablation zones slightly increased (-83% vs. +17%, p = 0.001). There were several imaging-only findings: Branch portal vein thrombus with both histotripsy (7/8) and MW (6/6), hematoma in 2/6 MW only, and a gallbladder injury in 1/6 MW animals. The ablation zones demonstrated complete cellular destruction for both modalities. CONCLUSION: Histotripsy was associated with more spherical treatments, fewer biliary complications, and greater treatment zone involution. Hepatic MW and histotripsy treatment in a normal porcine model appear at least equally effective for creating treatment zones with a similar safety profile. KEY POINTS: • Microwave ablation and histotripsy for liver treatment in a healthy porcine model yield equivalent procedural tolerance and cellular destruction. • Histotripsy was associated with more spherical treatments, fewer biliary complications, and greater treatment zone involution over the 28-day follow-up period. • These findings confirm the safety and efficacy of hepatic histotripsy and support the pursuit of clinical trials to further evaluate the translatability of these results.

A Cathepsin-Targeted Quenched Activity-Based Probe Facilitates Enhanced Detection of Human Tumors during Resection.

PURPOSE: Fluorescence-guided surgery using tumor-targeted contrast agents has been developed to improve the completeness of oncologic resections. Quenched activity-based probes that fluoresce after covalently binding to tumor-specific enzymes have been proposed to improve specificity, but none have been tested in humans. Here, we report the successful clinical translation of a cathepsin activity-based probe (VGT-309) for fluorescence-guided surgery. EXPERIMENTAL DESIGN: We optimized the specificity, dosing, and timing of VGT-309 in preclinical models of lung cancer. To evaluate clinical feasibility, we conducted a canine study of VGT-309 during pulmonary tumor resection. We then conducted a randomized, double-blind, dose-escalation study in healthy human volunteers receiving VGT-309 to evaluate safety. Finally, we tested VGT-309 in humans undergoing lung cancer surgery. RESULTS: In preclinical models, we found highly specific tumor cell labeling that was blocked by a broad spectrum cathepsin inhibitor. When evaluating VGT-309 for guidance during resection of canine tumors, we found that the probe selectively labeled tumors and demonstrated high tumor-to-background ratio (TBR; range: 2.15-3.71). In the Phase I human study, we found that VGT-309 was safe at all doses studied. In the ongoing Phase II trial, we report two cases in which VGT-309 localized visually occult, non-palpable tumors (TBRs = 2.83 and 7.18) in real time to illustrate its successful clinical translation and potential to improve surgical management. CONCLUSIONS: This first-in-human study demonstrates the safety and feasibility of VGT-309 to label human pulmonary tumors during resection. These results may be generalizable to other cancers due to cathepsin overexpression in many solid tumors.

Palisading granulomatous dermatitis and panniculitis (palisading granuloma) of dogs.

Palisading granulomatous dermatitis and panniculitis is recognized in various cutaneous inflammatory lesions secondary to presumed collagen damage. Cutaneous nodules with a palisading arrangement of histiocytes surrounding foci of collagen degeneration have been clinically termed palisading granuloma in dogs. Study aims were to characterize the cellular infiltrate of canine palisading granuloma and document salient clinical features. Inclusion criteria were met for 36 dogs and encompassed nodular dermal and subcutaneous histiocyte-predominant cellular infiltrates targeting and enveloping collagen fibers/necrotic foci with palisading configurations. Infectious causes were ruled out via standard histochemical stains and/or clinical data. Medical records were reviewed for signalment, clinical features, treatment, outcome, and comorbidities. Immunohistochemistry (IBA1, CD204, E-cadherin) and Masson's trichrome stain were used to assess histiocytic populations and dermal collagen, respectively. The histiocytes had moderate or strong immunolabeling for IBA1 and CD204 in 36/36 dogs (100%) and mild positive immunolabeling for E-cadherin in 3/36 dogs (8%). Alteration of collagen was graded as moderate or strong in 32/36 dogs (89%) and mild in 3/36 dogs (8%). Large breeds predominated with 30/36 dogs (83%) being ≥23 kg. Focal nodules were identified in 31/36 dogs (86%). The head/face were involved in 19/36 dogs (53%) and the extremities in 18/36 dogs (50%). Lesions from the 5/36 dogs (14%) with multiple nodules contained prominent eosinophilic infiltrates. Following excision, there was no evidence of recurrence. In conclusion, palisading granulomas are a distinct, non-neoplastic, histiocyte-predominant inflammatory condition in dogs associated with altered dermal collagen and favorable prognosis.

Probable cutaneous adverse drug reaction due to a cannabidiol-containing hemp oil product in a dog.

BACKGROUND: Cannabidiol (CBD) in hemp oil has become a widely used product in veterinary medicine. To date, there have been no reports of cutaneous adverse events associated with CBD-containing oil in the veterinary literature. CLINICAL SUMMARY: A 4-year-old castrated male Labrador retriever presented with pad sloughing and rapidly progressive cutaneous and mucosal ulceration within five days of administering an oral CBD oil product. Histopathological findings in combination with cutaneous signs were consistent with Stevens-Johnson syndrome. All lesions completely resolved after discontinuation of the hemp oil in addition to a 12 day course of cephalexin and prednisone. Given the lack of alternative causes including other medications, an adverse drug event was deemed probable according to the Naranjo algorithm. CONCLUSIONS AND CLINICAL IMPORTANCE: To the best of the authors' knowledge, this is the first report of suspected cutaneous adverse drug reaction to a CBD-containing hemp oil product.

Postmortem urinary tract changes in cats with urethral obstruction.

OBJECTIVE: To report the gross and histopathological postmortem findings of the urinary tract and compare them to clinical severity of disease in cats with urethral obstruction (UO). DESIGN: Retrospective, observational, descriptive study. SETTING: University teaching hospital. ANIMALS: Fourteen cats from 2000 to 2014 with UO that had a complete postmortem examination. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Bladder lesions were moderate-severe in 10 of 14 (71%) and mild in 4 of 14 (29%) cats. Bladder lesions were diffuse in 8 of 14 (57%), multifocal in 3 of 14 (21%), and focal in 3 of 14 (21%) cats. Lymphocytic cystitis was noted in 11 of 14 cats (78%), and neutrophilic cystitis was noted in 10 of 14 (71%) bladders. Urethral lesions were moderate-severe in 4 of 14 (29%), mild in 4 of 14 (29%), and no urethral lesions were identified in 6 of 14 (43%) cats. Ureteral lesions were mild in 1 of 14 (7%), and no ureteral lesions were identified in 13 of 14 (93%) cats. There were moderate-severe histopathological renal lesions in 5 of 14 cats (36%), mild renal lesions in 6 of 14 (43%), and no renal lesions were identified in 3 of 14 cats (21%). Renal lesions were multifocal in 10 of 14 (71%) and regional in 1 of 14 cats (7%). In the kidneys, the most common inflammatory infiltrate was lymphoplasmacytic. The severity of urethral lesions was not associated with the severity of bladder lesions (P = 1.0). Hyperkalemia paralleled the severity of bladder (P = 0.02) and renal lesions (P = 0.04). An association between the severity of bladder lesions and degree of azotemia could not be determined due to small sample size and removal of the most azotemic cats. CONCLUSIONS: Substantial renal and urinary bladder inflammatory lesions were found in cats with UO. The severity of these findings paralleled the severity of blood potassium concentrations.

Discriminatory features of acute eosinophilic dermatitis with oedema (Wells-like syndrome) and sterile neutrophilic dermatosis (Sweet's-like syndrome) in dogs.

BACKGROUND: Canine acute eosinophilic dermatitis with oedema (CAEDE) and sterile neutrophilic dermatosis have overlapping clinical and histopathological features. HYPOTHESIS/OBJECTIVES: The objective of this study was to identify features that differentiate these entities. ANIMALS: Forty dogs. METHODS AND MATERIALS: Retrospective case series. Forty cases with diagnoses of either CAEDE and/or sterile neutrophilic dermatosis were included based on histopathological review. Medical records (29 of 40 dogs) were reviewed for clinical findings and historical data. Commercially available immunohistochemical stains for granulocytes and a Luna stain were performed (40 of 40 dogs) to assess the granulocytic infiltrate. RESULTS: Nineteen cases had been previously diagnosed as CAEDE, seven cases had been designated as sterile neutrophilic dermatosis and 14 cases had overlapping features. Based on review and receiver operating characteristic (ROC) curve analysis, 30 cases with >12% eosinophils, enumerated by Luna staining, were diagnosed as eosinophilic dermatitis and oedema. Ten cases were diagnosed as sterile neutrophilic dermatosis. Dogs with CAEDE frequently had gastrointestinal signs (24 of 30;80%) and pruritus (11 of 30;33%). In dogs with sterile neutrophilic dermatosis, five of 10 (50%) had diagnoses of or histories compatible with immune-mediated polyarthropathy. CONCLUSIONS AND CLINICAL IMPORTANCE: In this case series, CAEDE was encountered more frequently than neutrophilic dermatosis and could be distinguished by the eosinophilic infiltrate, aided by a Luna stain. Concurrent arthralgia was more frequently identified with neutrophilic dermatosis. It remains unclear whether CAEDE and sterile neutrophilic dermatosis are separate disease entities or varied manifestations of the same disease.

Canine ischaemic dermatopathy: a retrospective study of 177 cases (2005-2016).

BACKGROUND: Ischaemic dermatopathy encompasses a poorly understood subset of canine diseases that share similar clinical and histological features. Very little information is currently available regarding population characteristics, progression and outcome. HYPOTHESIS/OBJECTIVES: This study aimed to describe the clinical features and therapeutic outcomes of ischaemia dermatopathy, excluding familial dermatomyositis, using cases diagnosed by histopathological analysis. ANIMALS: One hundred and seventy-seven cases submitted for histopathological analysis between 2005 and 2016 met inclusion criteria, of which 93 had complete medical records available. METHODS AND MATERIALS: Both records and pointed surveys were used to retrieve information. Scoring systems were created to subjectively evaluate clinical outcomes and likelihood of a vaccine association. RESULTS: Of 177 cases, toy and miniature poodles, Chihuahuas, Maltese, Yorkshire terriers and Jack Russell terriers were significantly over-represented (P < 0.001). Of the 93 cases for which historical data were obtained, median age at skin biopsy was five years (0.42-13 years) and median body weight was 7.3 kg (range 1.32-50.3 kg). The condition in 45 dogs (48.3%) was found likely to be associated with vaccination. Younger ages (P = 0.011) and higher body weights (P = 0.003) were positively correlated with greater likelihood of vaccination. Body weight <10 kg (P = 0.0045) and older ages (P = 0.0048) were significantly associated with worse outcomes. CONCLUSIONS AND CLINICAL IMPORTANCE: This study provides support for breed predispositions and identifies potential prognostic factors. Importantly, over half of the cases were considered unlikely to be vaccine-associated, demonstrating the need to investigate other underlying causes of this condition.

Clinical and histologic features of acute-onset erythroderma in dogs with gastrointestinal disease: 18 cases (2005-2015).

OBJECTIVE To describe the clinical and histologic features of acute erythroderma in dogs with gastrointestinal disease. DESIGN Retrospective case series. ANIMALS 18 dogs with erythroderma and gastrointestinal disease. PROCEDURES Medical records and biopsy specimens were reviewed. Information collected from medical records included signalment, clinical signs, physical examination and diagnostic test results, treatment, and outcome. The Naranjo algorithm was used to estimate the probability of an adverse drug reaction for each dog. RESULTS All dogs had an acute onset of erythematous macules or generalized erythroderma. Histologic features of skin biopsy specimens had 3 patterns representing a progressive spectrum of inflammation. Most dogs had vomiting (n = 17) and hematochezia (10). Signs of gastrointestinal disease became evident before, after, or concurrent with the onset of skin lesions in 10, 3, and 5 dogs, respectively. Inflammatory bowel disease, pancreatitis, and adverse food reaction were diagnosed in 5, 3, and 3 dogs, respectively. The cause of the gastrointestinal signs was not identified for 8 dogs. Eight dogs had a Naranjo score consistent with a possible adverse drug reaction. Treatment of skin lesions included drug withdrawal (n = 15), antihistamines (16), and corticosteroids (14). Signs of gastrointestinal disease and skin lesions resolved at a mean of 4.6 days and 20.8 days, respectively, after onset. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated acute erythroderma may be associated with > 1 gastrointestinal disease or an adverse drug reaction in some dogs. Recognition of the clinical and histologic features of this syndrome is essential for accurate diagnosis.

Percutaneous cholecystocentesis in cats with suspected hepatobiliary disease.

Objectives The objective was to evaluate the safety and diagnostic utility of percutaneous ultrasound-guided cholecystocentesis (PUC) in cats with suspected hepatobiliary disease. Methods Medical records of 83 cats with suspected hepatobiliary disease that underwent PUC were retrospectively reviewed. Results At the time of PUC, at least one additional procedure was performed in 79/83 cats, including hepatic aspiration and/or biopsy (n = 75) and splenic aspiration (n = 18). Complications were noted in 14/83 cases, including increased abdominal fluid (n = 11), needle-tip occlusion (n = 1), failed first attempt to penetrate the gall bladder wall (n = 1) and pneumoperitoneum (n = 1). There were no reports of gall bladder rupture, bile peritonitis or hypotension necessitating treatment with vasopressor medication. Blood products were administered to 7/83 (8%) cats. Seventy-two cats (87%) survived to discharge. Of the cats that were euthanized (9/83) or died (2/83), none were reported as a definitive consequence of PUC. Bacteria were identified cytologically in 10/71 samples (14%); all 10 had a positive aerobic bacterial culture. Bile culture was positive in 11/80 samples (14%). Of the cases with a positive bile culture, cytological description of bacteria corresponded to the organism cultured in fewer than 50% of cases. The most common cytologic diagnosis was hepatic lipidosis (49/66). The most common histopathologic diagnosis was cholangitis (10/21). Conclusions and relevance PUC was safe in this group of cats with suspected hepatobiliary disease. Complications were likely associated with ancillary procedures performed at the time of PUC. Bile analysis yielded an abnormal result in nearly one-third of cats with suspected hepatobiliary disease. Complete agreement between bile cytology and culture was lacking. Further evaluation of the correlation between bile cytology and bile culture is warranted.

Localized parakeratotic hyperkeratosis in sixteen Boston terrier dogs.

BACKGROUND: Although zinc responsive dermatosis is typically a disorder of Arctic breed dogs, this study identifies similar cutaneous lesions on the face and pressure points of Boston terrier dogs. HYPOTHESIS/OBJECTIVES: To document the clinical and histological features of localized parakeratotic hyperkeratosis of Boston terrier dogs, to determine if the lesions respond to zinc supplementation and to determine whether tissue zinc levels were decreased in affected versus unaffected dogs. MATERIAL AND METHODS: Sixteen Boston terrier dogs with similar gross and histological findings were identified retrospectively from two institutions. Follow-up information for nine dogs from one institution was obtained from referring veterinarians using a questionnaire. Tissue zinc levels were measured from formalin-fixed paraffin-embedded skin biopsy samples of affected and unaffected dogs using inductively coupled plasma mass spectrometry. RESULTS: Mild to severe parakeratotic hyperkeratosis with follicular involvement was present in all 16 cases. Of the nine dogs for which follow-up information was available, five dogs received oral zinc supplementation and four dogs had documented clinical improvement or resolution of dermatological lesions. The median skin zinc levels were not significantly different between affected and unaffected dogs. CONCLUSIONS AND CLINICAL IMPORTANCE: To the best of the authors' knowledge this is the first report of localized parakeratotic hyperkeratosis in Boston terrier dogs, some of which improved with oral zinc supplementation. Prospective studies in Boston terrier dogs are warranted to document potential zinc deficiency (serum and/or tissue levels, pre- and post-treatment) and to objectively assess response to zinc supplementation and other therapies.

Longitudinal Evaluation of the Skin Microbiome and Association with Microenvironment and Treatment in Canine Atopic Dermatitis.

Host-microbe interactions may play a fundamental role in the pathogenesis of atopic dermatitis, a chronic relapsing inflammatory skin disorder characterized by universal colonization with Staphylococcus species. To examine the relationship between epidermal barrier function and the cutaneous microbiota in atopic dermatitis, this study used a spontaneous model of canine atopic dermatitis. In a cohort of 14 dogs with canine atopic dermatitis, the skin microbiota were longitudinally evaluated with parallel assessment of skin barrier function at disease flare, during antimicrobial therapy, and post-therapy. Sequencing of the bacterial 16S ribosomal RNA gene showed decreased bacterial diversity and increased proportions of Staphylococcus (S. pseudintermedius in particular) and Corynebacterium species compared with a cohort of healthy control dogs (n = 16). Treatment restored bacterial diversity with decreased proportions of Staphylococcus species, concurrent with decreased canine atopic dermatitis severity. Skin barrier function, as measured by corneometry, pH, and transepidermal water loss also normalized with treatment. Bacterial diversity correlated with transepidermal water loss and pH level but not with corneometry results. These findings provide insights into the relationship between the cutaneous microbiome and skin barrier function in atopic dermatitis, show the impact of antimicrobial therapy on the skin microbiome, and highlight the utility of canine atopic dermatitis as a spontaneous nonrodent model of atopic dermatitis.

Computed tomographic characteristics of odontogenic neoplasms in dogs.

Odontogenic neoplasms are locally invasive oral tumors in dogs. The purpose of this retrospective study was to describe CT characteristics for varying histopathologic types of canine odontogenic neoplasms. A board-certified veterinary radiologist who was unaware of histologic findings reviewed and scored imaging studies. A total of 29 dogs were included in the study. Twenty-three of these dogs had concurrent dental radiographs. The most common CT characteristics for all tumor types were a direct association with or in the region of multiple teeth in 96.4% (27/28), contrast enhancement in 96.3% (26/27), alveolar bone lysis in 93.1% (27/29), and mass-associated tooth displacement in 85.2% (23/27). Mass-associated cyst-like structures were identified in 53.6% (15/28) and were only present in tumors containing odontogenic epithelium. Canine acanthomatous ameloblastomas (n = 15) appeared as extra-osseous (10/15) or intra-osseous (5/15) masses. Intra-osseous canine acanthomatous ameloblastomas were more likely to have mass-associated cyst-like structures and were subjectively more aggressive when compared with extra-osseous canine acanthomatous ameloblastomas. Amyloid-producing odontogenic tumors (n = 3) had subjectively uniform CT imaging characteristics and consisted of round soft tissue and mineral attenuating masses with multiple associated cyst-like structures. Fibromatous epulides of periodontal ligament origin (n = 4) were contrast enhancing extra-osseous masses that were rarely referred for CT examinations and 25% (1/4) were not visible with CT. Other odontogenic tumors were less represented or had more variable CT imaging characteristics. Mass-associated tooth destruction was appreciated more often with dental radiographs and extra-oral tumor extension was identified more often with CT.

Clinicopathological findings of canine seborrhoeic keratosis with comparison to pigmented viral plaques.

BACKGROUND: Seborrhoeic keratoses (SKs) are common benign epidermal neoplasms in humans and are rarely diagnosed in the dog. These circumscribed, raised, variably pigmented plaques arise in middle aged to older humans, with a focal or multicentric distribution; although common, the underlying cause of these lesions is not known. Although less common in the dog, the lesions are similar and have features that overlap with papillomavirus-associated pigmented viral plaques. HYPOTHESIS/OBJECTIVES: Seborrhoeic keratoses in the dog are negative for canine papillomavirus. ANIMALS: Eleven cases of SK from a 12 year period were reviewed. METHODS: This was a retrospective study of the histopathological findings and case histories. Complete clinical records following collection of the skin biopsy were available in five of 11 cases. Immunohistochemistry was performed for all cases; PCR analysis was carried out for papillomavirus in six cases. RESULTS: Histologically, SKs had an exophytic to mildly endophytic epidermal proliferation, creating a papillomatous to acanthotic, hyperkeratotic, frequently pigmented plaque. There was an absence of hypergranulosis or viral cytopathic effect; PCRs for canine papillomavirus within the formalin-fixed paraffin-embedded skin biopsies were negative. No breed, sex or site predilection was recognized. The mean age at biopsy of the lesions was 8.8 years (range 5-14 years). CONCLUSIONS AND CLINICAL IMPORTANCE: Histopathological features and negative papillomavirus status distinguish SK as an important differential diagnosis for pigmented viral plaques in dogs.