Congenital non-epidermolytic ichthyosis was diagnosed in two littermate mixed-breed Yorkshire terrier puppies. Histopathological results confirmed lamellar orthokeratosis; genetic testing for known mutations was negative. Topical treatment improved clinical signs, yet relapse occurred upon discontinuation. This case expands the breeds affected and emphasises the need for life-long management.
Background: Zinc-responsive dermatosis, characterised by parakeratotic hyperkeratosis, is most commonly reported in Arctic breeds and, more recently, suspected in Boston terriers.
Objectives: To describe the clinical and histological features of pinnal parakeratotic hyperkeratosis in French bulldogs, evaluate the response to zinc supplementation, and compare tissue zinc concentrations between affected and unaffected dogs.
Materials and methods: Sixteen French bulldogs with histologically confirmed parakeratotic hyperkeratosis were identified retrospectively across the United States. Follow-up information was obtained from medical records and owner email surveys. Tissue zinc concentrations were measured by inductively coupled plasma mass spectrometry in skin biopsy samples from affected and control French bulldogs.
Results: All 16 dogs had bilateral pinnal hyperkeratosis; six also had lesions on the nasal bridge, scrotum or tail. Of 12 dogs that received oral zinc supplementation, eight (67%) improved or achieved complete resolution, including four that responded to zinc supplementation alone. Relapse occurred in four dogs following discontinuation of supplementation, with improvement in three upon reintroduction. Tissue zinc concentrations did not differ significantly between affected and control biopsy samples.
Conclusions and clinical relevance: French bulldogs may be predisposed to pinnal parakeratotic hyperkeratosis suggestive of zinc-responsive dermatosis. Zinc methionine supplementation at approximately 2 mg/kg/day was associated with clinical improvement in most cases. Prospective studies are warranted to clarify pathogenesis, compare zinc formulations, and establish diagnostic and therapeutic guidelines.
Background: Apoptotic keratinocytes have been described with canine epitheliotropic cutaneous T-cell lymphoma (eCTCL) without further detailed characterisation of this feature.
Hypothesis/objectives: This study aims to characterise confirmed eCTCL cases enriched with apoptotic keratinocytes as a novel cytotoxic variant of canine eCTCL.
Animals: Canine eCTCL cases from a veterinary pathology diagnostic laboratory database were searched from 2018 to 2024.
Materials and methods: Haematoxylin and eosin-stained slides were examined for evidence of lymphocytes, apoptotic keratinocytes with lymphocytic satellitosis, and epitheliotropism in the lower half of the epidermis and adnexal structures by a board-certified veterinary pathologist. Immunohistochemical (IHC) staining for CD3 and CD20 was performed in addition to clinical follow-up with response to treatment, and PCR for Antigen Receptor Rearrangement (PARR) assay (T and B cell).
Results: Six cases with representative features were identified. Various breeds were affected with a median age of 10 years at presentation. Skin lesions included generalised crusting, scaling, erythema and erosions/ulcerations; mucocutaneous junctions were involved in three of six dogs. Histopathological results confirmed an interface cytotoxic pattern eCTCL in all cases, marked by lymphocytic epitheliotropism and apoptotic keratinocytes. IHC staining demonstrated > 90% strong CD3+ T-cell immunoreactivity in the epidermis and follicular epithelium in all cases. All six confirmed cases showed clonality for the T-cell receptor gene using PARR analysis.
Conclusions and clinical relevance: This cytotoxic variant of canine eCTCL clinically and histologically can resemble other cutaneous diseases with cytotoxic dermatitis (e.g., hyperkeratotic erythema multiforme). IHC and clonality testing and monitoring response to treatment may be necessary for definitive diagnosis.
Background: Lapatinib is widely used in human oncology; however, dermatological adverse events (DAEs) are common and have been correlated with treatment efficacy. In veterinary medicine, lapatinib use in combination with piroxicam has been shown to be effective in treating canine urothelial carcinoma (UC); however, the incidence and prognostic significance of DAEs in dogs remain unknown.
Objective: To evaluate the DAEs in dogs with UC treated with lapatinib and piroxicam.
Animals: Eighty-five dogs with UC were treated with lapatinib/piroxicam and 42 were treated with piroxicam alone.
Materials and methods: This retrospective cohort study evaluated dogs diagnosed with UC and treated with lapatinib and piroxicam, and those treated with piroxicam alone. Relevant data were extracted from the medical records. The DAEs were assessed using the Veterinary Cooperative Oncology Group Common Terminology Criteria for Adverse Events and Naranjo algorithm. The log-rank test and Cox proportional hazards model were used to assess progression-free survival (PFS).
Results: DAEs occurred in 31.8% of the dogs in the lapatinib/piroxicam group, with alopecia and hyperpigmentation being the most common. In the piroxicam group, DAEs were observed in 7.1% of dogs. The relative risk of developing DAEs in the lapatinib/piroxicam group was 4.4 (p < 0.01). In the lapatinib/piroxicam group, DAEs were associated with a longer PFS (p < 0.03). The Cox proportional hazards model identified DAEs as independent prognostic factors for improved PFS (hazard ratio, 0.52, p < 0.05).
Conclusions and clinical relevance: Lapatinib treatment in dogs induces DAEs, which serve as biomarkers of lapatinib efficacy in canine UC.
Background: Poodles and poodle cross-breds develop a poorly described dorsal truncal hair coat condition informally called "doodle dysplasia".
Hypothesis/objective: To characterise the clinical, histopathological and epidemiological features of dorsal melanotrichia in poodles and poodle crosses.
Animals: Twenty-nine privately-owned poodles and poodle cross-breds with an unidentified cause for dorsal melanotrichia in the United States.
Materials and methods: Retrospective and prospective case recruitment from private/academic dermatology and general practices, and involved record review, owner questionnaire, and dermatohistopathological analysis between 2019 and 2024. Inclusion criteria were poodles and poodle cross-breds with coat colour changes restricted to the dorsum, with or without other concurrent dermatological lesions or systemic signs.
Results: The average age of onset was 4 years. Summer was the most commonly reported season of onset (46% dogs), and recent grooming was noted in 57% of dogs with the information available. The most common pattern and distribution were serpiginous in 67% of dogs, and dorsal thorax and lumbar in 39% of dogs. Additional changes were alopecia and alteration of texture. Of those dogs with resolution, 71% had recurrence of coat colour and texture alterations 12 months or 24 months later. Histopathological changes were overall mild, with the most common being outer root sheath apoptosis and altered pigmentation in follicles, without strong evidence to support a dysplasia.
Conclusion and clinical relevance: "Doodle dysplasia" is a condition with a possible seasonal and/or environmental component. Given the lack of clear evidence for dysplasia, we propose a new name: dorsal melanotrichia of poodles and poodle crosses.
Background: Dermoscopy is a non-invasive technique used to preliminary assess skin lesions in humans and, more recently, in animals. Calcinosis cutis (CC) is an uncommon condition in dogs characterised by cutaneous calcification typically secondary to iatrogenic hyper-glucocorticism or endogenous hyper-adrenocorticism.
Objectives: The aim of this study was to describe and characterise the dermoscopic features of CC in dogs affected by hyper-cortisolism, either iatrogenic or spontaneous, and assess the inter-observer agreement of the dermoscopic parameters.
Materials and methods: Twelve lesions from 12 client-owned dogs, histologically diagnosed as CC associated with spontaneous or iatrogenic hyper-cortisolism, were included in this study. Dermoscopic images of the lesions at ×10 magnification were independently evaluated on a computer screen by three ECVD board-certified veterinary specialists and one ECVD resident.
Results: At ×10 magnification, all lesions exhibited single or multiple structureless bright white areas and erythema. In eight of the 12 lesions, these white areas surrounded prominent plugs of yellowish-to-brown material emerging from follicular ostia and/or epidermal ulcerations. The main vascular pattern was dominated by a single vessel type (monomorphic pattern), consisting mainly of short, dilated, linear curved vessels (seven of 12), with short linear vessels observed in four lesions. Histopathological results confirmed that the white structures observed dermoscopically corresponded to calcium deposits within the dermis. A specific association was not observed between dermoscopic features and the distribution or localisation of mineralisation described in the histological evaluations.
Conclusions and clinical relevance: Dermoscopy represents a useful technique to assess CC in dogs.
Background: An increased number of dogs with unresolved yeast otitis externa (OE) after miconazole treatment was observed at a tertiary practice.
Hypothesis/objectives: To evaluate miconazole susceptibility in Malassezia pachydermatis isolates from canine OE.
Animals: Eleven client-owned dogs (16 ears) with clinical and video otoscopic signs of OE and cytological evidence of yeast.
Materials and methods: Yeast cultures were derived from ear swabs. PCR amplified portions of the internal transcribed spacer region (ITS), and partial sequences encoding the 18S rRNA small subunit (SSU), 26S rRNA large subunit (LSU), and actin (ACT1) loci for phylogenetic analysis, as well as the ERG11 gene that encodes lanosterol 14α-demethylase. Miconazole susceptibility was assessed by disk diffusion on Mueller-Hinton agar. Molecular modelling was used to evaluate the relationship between lanosterol 14α-demethylase amino acid substitutions and miconazole susceptibility.
Results: Isolates of M. pachydermatis from canine OE formed a three-clade phylogeny. Most ERG11 mutations predicted lanosterol 14α-demethylase substitutions that were clade-specific without an effect on miconazole susceptibility. Reduced susceptibility was associated with substitutions of amino acid A302, located in the lanosterol 14α-demethylase azole-binding site. Other altered amino acids were located elsewhere in the lanosterol 14α-demethylase protein without an apparent effect on miconazole binding.
Conclusions and clinical relevance: Clinical isolates of M. pachydermatis with reduced miconazole susceptibility were easily found, suggesting that miconazole resistance is present in routine patients. Lanosterol 14α-demethylase interactions with longer-tailed azoles involve additional contacts beyond A302 suggesting these drugs will be more effective against miconazole-resistant strains. However, effective antifungal stewardship is needed to slow development of pan-azole resistance that would limit treatment options for dogs with M. pachydermatis-associated disease.
Background: Cold atmospheric plasma (CAP) offers a novel, nonpharmacological approach with potent antimicrobial, anti-inflammatory and wound-healing properties without harming healthy tissue. In vitro studies have demonstrated its antimicrobial efficacy against key pathogens implicated in canine otitis externa (OE), a condition prone to chronicity if poorly managed.
Objectives: This study evaluated CAP's therapeutic efficacy and safety in treating canine acute OE.
Animals: Twenty-two dogs with bilateral acute OE.
Materials and methods: Dogs were divided into two equal groups with different bilateral treatment protocols. In Group 1, one ear was treated twice daily with topical antibiotic/antifungal/corticosteroid for 10 days (STD1), while the opposite ear was treated with CAP on Day (D)0 and D5 (CAP1). In Group 2, one ear received the same topical drug protocol (STD2), while CAP was applied to the opposite ear on D0, D3, D6 and D9. 0-3 otitis index score (OTIS-3) and cytological score were assessed on D0, D5, D10 and D15. Treatment response was assessed by the investigator and owners on D5, D10 and D15.
Results: Significant reductions in OTIS-3 and cytological score were observed over time in both CAP groups, similar to STD groups (p < 0.01). Treatment response in CAP groups was rated good-to-excellent by nearly all investigators and owners. CAP demonstrated high tolerability, with no adverse effects.
Conclusions and clinical relevance: CAP may represent a promising adjunctive therapy in the management of acute OE.
Background: Dermatophytes can be isolated from both symptomatic and asymptomatic cats, yet the role of skin commensals in modulating disease expression remains unclear. This study investigates whether microbial skin communities influence the clinical presentation (symptomatic or asymptomatic) of dermatophyte infection in Persian cats.
Hypothesis/objectives: We hypothesised that the fungal and bacterial skin microbiota differ between Persian cats with and without clinical signs of dermatophytosis. The objectives of this study were to compare the fungal and bacterial skin microbiota among healthy, symptomatic, and asymptomatic cats with dermatophytosis and to evaluate the performance of two skin sampling methods (carpet and toothbrush) for microbiome analysis.
Animals: Forty-five cats.
Material and methods: Cats were grouped according to clinical presentation: Persian cats with skin lesions characteristic of dermatophytosis (multifocal alopecia and scaling) and a positive fungal culture (symptomatic group; n = 15), Persian cats with no skin lesions and a positive fungal culture (asymptomatic group; n = 15), and domestic short hair cats with no history and clinical signs of skin disease and negative fungal culture (negative group; n = 15). Hair and scale samples were collected using carpet and toothbrush techniques from all animals. Fungal and bacterial communities were investigated using high-throughput sequencing targeting internal transcribed spacer (ITS)1 and 16S ribosomal (r)RNA genes.
Results: Our data showed that the taxonomic composition of fungal and bacterial communities was similar between symptomatic and asymptomatic cats, regardless of the sampling method used. No notable differences were identified in the relative abundance of Microsporum spp. between symptomatic and asymptomatic cats.
Conclusions and clinical relevance: Our findings suggest that the commensal microbiota may not influence the clinical presentation of dermatophyte infection. Instead, other factors, such as the host immune response, appear to play a pivotal role in determining disease outcomes.
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