Dermoscopic evaluation of normal canine skin with a handheld dermoscope

Abstract

Background

Dermoscopy is a noninvasive diagnostic tool that provides a magnified view of skin structures. While dermoscopy is described for certain canine dermatological diseases, large‐scale studies evaluating normal skin are lacking.

Hypothesis/Objective

This study aimed to correlate dermoscopic findings with histopathological results in healthy canine skin to enhance understanding of dermoscopic microanatomy and pigmentation patterns.

Animals

Healthy, adult, shelter dogs (n = 121).

Materials and Methods

After general anaesthesia for prescheduled sterilisation procedures, four regions on each dog were assessed using a handheld dermoscope followed by collecting a biopsy for histopathological investigation. Dermoscopic assessment included skin colour and pattern, presence of scale and blood vessel number. Dermoscopic findings were correlated with histopathological characteristics.

Results

Dermoscopy identified grey as the most common skin colour, diffuse as the primary pattern, most commonly mild scale and primarily absent blood vessels. Dermoscopy correlation with histopathological results identified moderate scale as more likely to have hyperkeratosis, and no significant correlation between visualised blood vessels and number of endothelial cells. Furthermore, the dermoscopic colour brown was more likely to have melanin within each epidermal layer, while white was less likely to have melanin within each layer. Despite the lack of gross and dermoscopic inflammation, such as erythema, 53 of 484 sites had histopathological evidence of inflammation, with primarily mild mastocytic and eosinophilic superficial dermatitis.

Conclusions and Clinical Relevance

Dermoscopy can identify characteristics in canine skin that correlate with histopathological results, yet mild inflammation may remain undetected. This correlation better establishes baselines for future studies utilising dermoscopy when assessing dermatological diseases.

Background – Dermoscopy is a noninvasive diagnostic tool that provides a magnified view of skin structures. While dermoscopy is described for certain canine dermatological diseases, large‐scale studies evaluating normal skin are lacking. Hypothesis/Objective – This study aimed to correlate dermoscopic findings with histopathological results in healthy canine skin to enhance understanding of dermoscopic microanatomy and pigmentation patterns. Conclusions and Clinical Relevance – Dermoscopy can identify characteristics in canine skin that correlate with histopathological results, yet mild inflammation may remain undetected. This correlation better establishes baselines for future studies utilising dermoscopy when assessing dermatological diseases.

INTRODUCTION

Dermoscopy is a noninvasive diagnostic method that provides a magnified view of the skin surface. ¹ Dermoscopy is commonly used to categorise human pigmented and nonpigmented skin lesions, assess follicular abnormalities and evaluate vascular patterns by assessing the specific colouration and patterns. ² , ³ The patterns are correlated to histopathological characteristics, allowing the noninvasive technique to diagnose diseases and refine when or where to take a lesion biopsy. ² , ³ , ⁴ Colouration on dermoscopy correlates with the nature of the pigment/structure and, in the case of melanin, the depth of the pigment observed on histopathological evaluation. ² , ⁴ , ⁵ Depth also determines the colour of haemoglobin, where superficial blood vessels, such as capillaries, appear red/pink, deeper blood vessels appear blue/purple and haemorrhaged blood appears brown/yellow. ¹ , ² , ⁴ , ⁵

There are limited dermoscopy studies in veterinary medicine. Normal feline and equine skin have been assessed with a handheld dermoscope, and biopsies of the examined areas were taken for histopathological evaluation to allow for comparison between modalities. ⁶ , ⁷ , ⁸ , ⁹ These studies involved fewer than 30 animals with limited breed variation. ⁶ , ⁷ , ⁹

Canine studies have assessed several specific disease patterns, such as skin erythema, dermatophytosis, hair follicle growth rates and alopecia X, yet only small numbers and limited breed variations of normal dogs were evaluated as controls in these studies. ¹⁰ , ¹¹ , ¹² , ¹³ , ¹⁴ , ¹⁵ , ¹⁶ Therefore, while previous studies suggest a diagnostic benefit of dermoscopy in veterinary medicine, there have been no large‐scale studies evaluating the dermoscopic characteristics of normal canine skin. As dermoscopic differences between equine and feline skin have been described, it is reasonable to assume that canine skin also will have differences from other animal species on dermoscopy. ⁶ , ⁷ , ⁸ , ⁹ Given the significant variation in cutaneous and pelage characteristics with different canine breeds, such as skin and hair pigmentation, establishing normal features and their correspondence with histopathological structures is critical to provide a reference with which to later assess the diagnostic ability of dermoscopy for canine skin diseases.

This study aimed to establish dermoscopic features of healthy canine skin and to correlate those features with histopathological characteristics in order to enhance understanding of the microanatomy associated with dermoscopic findings with a handheld dermoscope.

MATERIALS AND METHODS

Animal use

This study was approved by the Institutional Animal Care and Use Committee of Arizona Veterinary Specialists.

Study population

The study population included healthy, adult, shelter dogs with pre‐scheduled surgical sterilisation. Dogs were of any intact sex, age (≥1 year), breed and size. Dogs without officially documented pedigree were classified as ‘mixed breed’. To further demonstrate the differences between mixed breed dogs, secondary factors such as the hair colour, pattern, coat structure, body size, furnishings (e.g. eyebrows, beard) and ear shape were described. ¹⁷

The dogs included were determined as healthy based on physical and dermatological examination. While the shelter environment did not allow for a detailed dermatological history, it was determined that no pruritic behaviour had been observed or reported before inclusion. Exclusion criteria included patients <1 year of age, and evidence of dermatological or systemic disease.

Dermatological evaluation

Dermatological examination was performed on dogs before preanaesthetic sedation and surgical preparation for sterilisation surgery. This would ensure that any iatrogenic changes in skin pigmentation were accounted for, such altered skin colouration resulting from vascular or blood pressure changes under general anaesthesia.

Anaesthetic protocol

The standardised anaesthetic protocol was pre‐medication with acepromazine (0.044 mg/kg; Boehringer Ingelheim Vetmedica) and butorphanol (0.4 mg/kg; Elanco) followed by induction with ketamine (5 mg/kg; Boehringer Ingelheim Vetmedica) and midazolam (0.25 mg/kg; Gland Pharma Ltd). General anaesthesia was then maintained with isoflurane gas administered to effect. Each dog in the study received the same anaesthetic protocol.

Dermoscopic evaluation

A contact polarised and noncontact nonpolarised light handheld dermoscope (Delta 30; Heine) was used to acquire images at ×10 magnification after induction of general anaesthesia from four regions on each dog. Polarised and nonpolarised images were collected at each site. The polarised contact images were obtained using a nonliquid contact plate, which was very lightly placed on each site to limit the pressure that could impact structure evaluation (Delta 30 Contact Plate; Heine). Areas assessed were the cranial aspect of the head, dorsal neck, caudal dorsum above the pelvis, and the inguinum approximately 2 cm to the left of the linea alba (Figure 1). This latter area was chosen to avoid interfering with healing from the sterilisation procedure. Each area was lightly clipped with a 6‐mm guard and images were acquired using a smartphone (iPhone11 Pro; Apple) directly connected to the dermoscope. A smartphone application (heine derm) stored patient information and dermoscope pictures with high‐resolution image quality up to 12 megapixels. All images were obtained by the same investigator, phone and dermoscope to reduce factors relating to variations in phone image sampling and colouration. Specific dermoscopic characteristics that were evaluated are summarised in Table 1 based on dermoscopic criteria characterised previously. ¹⁸ , ¹⁹ In order to confirm there were no differences in dermoscopic findings after sedation or general anaesthesia, an unblinded preliminary study comparing dermoscopic images pre‐ and post‐sedation or general anaesthesia was performed on seven healthy dogs (unpublished data). These dogs were not enrolled in the current study.

FIGURE 1.

Anatomical location of dermoscopic evaluation sites.

TABLE 1.

Dermoscopy characteristics described for each location.

Skin colouration	Pink, dark pink, brown, black, white, grey
Pattern of skin colouration	Diffuse: homogenous colouration Linear: parallel, reticular or perpendicular Pseudopod: finger‐like projection with nodular tip Circle: annular structure Clod: irregularly shaped structure Dotted: rounded structures <0.1 mm in diameter
Appearance of vasculature	None, linear, dotted, corkscrew, comma, hairpin
Degree of scale	None, mild (<30% of field of view), moderate (30%–60%), marked (>60%)

Biopsy and histopathological evaluation

Biopsy samples were collected under general anaesthesia to reduce stress and discomfort. Each dermoscopic site was marked with a Sharpie, lidocaine was then infused subcutaneously after dermoscopic imaging for local anaesthesia (maximum dose 5 mg/kg per dog; Sparkhawk Laboratories), and a 4‐ to 6‐mm punch biopsy tool was used to collect each skin sample including all skin layers (Disposable Biopsy Punch; Integra LifeSciences Production Corp). Sites were closed with a buried suture pattern within the dermis (3‐0 monocryl; Ethicon, Inc.). Skin samples were placed in 10% formalin in preparation for histopathological assessment. Samples were routinely processed longitudinally and stained using haematoxylin and eosin. ²⁰

The pathologist, who had a specific interest in dermatopathology, was blinded to the dermoscopic results. The evaluation of each sample included the presence and severity of hyperkeratosis, superficial dermis endothelial cell density, subjective degree of epidermal pigmentation, distribution of pigmentation within the epidermis and presence of subclinical inflammation. The immunohistochemical (IHC) marker for Factor VIII‐related antigen was used to identify endothelial cells within each sample. It was determined that documenting the total cells positive for Factor VIII would be a better representation of the amount of vasculature present in each sample instead of counting individual vessels. ²¹ If subclinical inflammation was present, the type, location and degree of inflammation was recorded.

Statistical methods

Data were assessed as either categorical or numerical data. Associations between categorical variables were assessed by the chi‐square test of association, or by Fisher's exact test when ≥20% of expected frequencies were <5. Most numerical variables were nonparametrically distributed, and correlation between numerical variables was measured by Spearman's rank correlation coefficient (rho). Summary statistics for numerical data are presented as median (range). p‐values <0.05 were considered statistically significant.

RESULTS

Signalment

A total of 122 dogs were enrolled in the study. One dog was excluded after sample collection owing to the subsequent diagnosis of hypothyroidism; therefore, 121 dogs were assessed. As a consequence of the pedigree paperwork not being present for any animal, all were categorised as mixed breed for accuracy, yet there were certain phenotypes noted such as three Great Dane phenotype, three Chihuahua phenotype, seven Poodle phenotype, seven German Shepherd dog phenotype and 19 Siberian Husky phenotype dogs. Eighty‐two dogs had a phenotype that was not suggestive of a particular breed. The mean patient age was 2.5 years, and there were 70 male and 51 female dogs. There were 14 small dogs (<20 lb), 39 medium dogs (20.1–45 lb), 56 large dogs (45.1–74 lb) and 12 extra‐large dogs (>74 lb) with a mean weight of 49.6 lb. Evaluated phenotypic characteristics were ear shape, hair length, hair structure, colour, pattern and furnishings (Table 2).

TABLE 2.

Secondary gross characteristics of study population.

Ear shape	Hair length	Hair structure	Hair colour	Hair pattern	Furnishings
60.3% dropped 39.6% upright	52.9% short 36.4% medium 10.7% long	76% straight 18.2% loose curl 4.1% tight curl 1.7% wiry	44.6% black 20.7% brown 15% white 9.8% tan 7.4% grey 1.7% yellow 0.8% red	28.9% solid colour 3.3% brindle 50.4% bicolour 2.5% pointed 7.4% tricolour 0.8% merle 5.0% spotted 1.7% sable	97% absent 3% present

Dermoscopy

There are subtle differences between the polarised and nonpolarised modalities, yet the dermoscopic characteristics measured were consistent and will be described as one moving forward. The hair follicles at each site were identified as compound hair follicles, including one primary, thicker hair and several (two to five) secondary, thinner hairs associated with each follicular pore. The hair shafts associated with one pore varied from all being one colour to having multiple colours represented. The inguinal location had the least amount of hair follicles noted, while the dorsal head had the most amount of hair follicles noted within the dermoscopy field‐of‐view.

The primary skin colour across all sites was grey (44%), followed by white (26%), brown (14%), light pink (11%), black (3%) and dark pink (<2%). The most common pigmentation pattern was diffuse (72.3%) and then clod (22.5%). The remaining samples were either line (2.1%), dotted (1%) or a combination of those patterns (2.1%) (Figure 2). Although most sites did not have visible vasculature (68%), when present there was an average of one to two vessels per site (range one to nine). When present the vessel morphology per evaluated site was dotted (41.3%), linear (38%) or comma (16.1%), with the remaining vessels showing a combination of appearances (4.6%) (Figure 3). Scale was absent in 38% of sites, mild in 56.8% and moderate in 5.2% (Figure 2). Presence of scale was significantly impacted by body site (p < 0.001), where the ventrum did not have scale in 65% of dogs and there was moderate scale on the head in 11% of dogs.

FIGURE 2.

Dermoscopic patterns: (a) brown linear pattern with white pattern; (b) brown clod pattern with white; (c) diffuse grey with overlying mild white scale; and (d) pink, brown, white and black colouration.

FIGURE 3.

Dermoscopic vasculature appearance: (a) black arrow identifies a comma vessel; white arrow identifies a dotted vessel; and (b) black arrowhead identifies a linear vessel. Picture exposure/colouration was adjusted to highlight vasculature.

Histopathological results

A total of 484 biopsy samples were evaluated (four sites per dog). There was no acanthosis noted in any sample. The subjective presence of hyperkeratosis was noted in 2.5% of samples, with the majority being mildly orthokeratotic (2.2%), while the remaining samples were classified as moderately orthokeratotic (0.3%). The superficial dermis endothelial cell density median was 44 cells at ×400 magnification (range 0–172). Epidermal pigment, specifically melanin, was absent in 34.7% of samples and subjectively mild in 54.6%, moderate in 10.1% and marked in 0.6%. Pigment distribution was multifocal in 48.1% and diffuse in 14.5% of samples.

There was inflammation in 53 sites (11%) from a total of 36 different dogs. The degree of inflammation was subjectively recorded as mild and moderate in 96% and 4% of sites, respectively. The location of inflammation was in the superficial dermis in 94.3% of samples, with the remaining present in the epidermis. The inflammatory pattern was superficial dermal mastocytic, eosinophilic, or a combination in 71.6% of sites, with other inflammatory patterns noted to be epidermal neutrophilic pustular (5.7%), superficial dermal lymphocytic, eosinophilic and mastocytic (20.8%) and perivascular lymphoplasmacytic (1.9%).

Dermoscopy association with histopathological results

The samples with moderate scale on dermoscopy were more likely to have at least mild hyperkeratosis on histopathological evaluation compared to the samples with none or mild dermoscopic scale (p = 0.022). When assessing the number of vessels found on dermoscopy to the number of endothelial cells found on histopathological evaluation, there was no significant correlation between these two findings (ρ = −0.034; p = 0.54). When comparing the dermoscopic primary skin colour to the presence of pigment in each epidermal layer, brown was more likely to be associated with pigment within each layer and white was less likely to have pigment within each layer (p < 0.001). While white skin colour was less likely to have pigment in each epidermal layer, there were still cases that had at least mild pigmentation present in each cell layer. There was no significant association in the number of blood vessels noted on dermoscopy and the presence of subclinical inflammation in samples (p = 0.49). Additionally, there was no association between the dermoscopic skin colours and the presence of subclinical inflammation (p = 0.21).

DISCUSSION

This study described different dermoscopic characteristics in 121 normal adult dogs and related those findings to histopathological results. This allows for a better understanding of canine cutaneous microanatomy associated with dermoscopic findings, benefiting future dermoscopic studies by providing a normal baseline.

When assessing the histopathological pigmentation within each of the epidermal layers to the primary dermoscopic skin colour, brown was more likely to have pigmentation in each layer, while white was less likely to have pigmentation within each layer. Because some dogs with white skin colour had pigment in the epidermal layers, dermoscopy may not reliably determine pigment density in normal skin.

The majority of dermoscopic images had white nonadherent scale present, while most histopathological samples did not have hyperkeratosis. Even though the overall degree of scale could not be correlated to hyperkeratosis, the samples with moderate dermoscopic scaling were more likely to have at least mild hyperkeratosis present. This finding could indicate that moderate scale is more indicative of hyperkeratosis on histopathological evaluation and mild scale could be a normal finding on dermoscopy.

Dermoscopy is often used to evaluate vasculature in human medicine as it correlates with histopathological structures. ² , ⁴ , ⁵ In this study, the number of vessels found on dermoscopy did not correlate with the number of endothelial cells on histopathological evaluation. This indicates that dermoscopy may underestimate the vascular density in normal skin.

Cutaneous inflammation often appears as red pigmentation change (erythema) owing to increased blood flow and increased blood vessel density. ²² When assessing the group with histopathological evidence of inflammation, there was no significant correlation with dermoscopic skin colour or vessel number. The lack of association between the subclinical inflammation group and dermoscopic skin colouration or density of dermoscopically visible vasculature suggests that this modality is not sensitive for detecting mild inflammation.

Limitations

The first limitation is that the population of dogs was categorised as mixed breed owing to the lack of pedigree paperwork, which prohibited correlation of dermoscopic variations with breed. However, this is a limitation of any study that does not use dogs with pedigree analysis. Another limitation was lightly clipping the areas before collecting dermoscopic images because, in theory, the clipping could have altered the skin's surface. However, a 6‐mm guard was utilised to limit the amount of skin surface trauma and dogs were assessed before clipping any hair. Additionally, clinicians will be likely to utilise light clipping to evaluate the skin surface on future dogs. Another potential limitation was having patients under general anaesthesia before performing the dermoscopic imaging and biopsy collections; however, this was considered important to minimise patient stress and discomfort of the biopsy sampling because each animal was already undergoing a sterilisation procedure.

Two types of dermoscopes are available: handheld and video dermoscope. The handheld dermoscope is a useful tool for evaluating pigmentation and vasculature patterns, yet can lack detail of the follicular openings and hair shaft thickness. ¹⁹ A handheld dermoscope was used during this study as a consequence of it being a more financially accessible tool and potentially more likely to be used by clinicians. A future study could utilise a video dermoscope for further assessment of hair shaft and pore characteristics in normal canine skin. Additionally, future studies could utilise both longitudinal and transverse histopathological orientation for additional interpretative parameters. While a potential limitation, the transverse histopathological orientation was not utilised in this study as longitudinal orientation of biopsies is the current standard and the transverse orientation is complex to carry out, requiring additional training and expertise and may not be routinely available in clinical practice. ¹⁴

CONCLUSION

This study demonstrated that certain dermoscopic characteristics in normal canine skin can correlate with histopathological characteristics. This large‐scale study provides an important baseline for future studies utilising dermoscopy to assess cutaneous changes and dermatological diseases in canines.

AUTHOR CONTRIBUTIONS

Rachael Loek: Investigation; funding acquisition; writing – original draft; writing – review and editing; methodology. David Gardiner: Formal analysis; investigation. George Moore: Formal analysis; writing – review and editing; writing – original draft. Ashfaq Marghoob: Conceptualization; funding acquisition; resources. Carine Laporte: Conceptualization; funding acquisition; writing – review and editing; methodology; supervision.

FUNDING INFORMATION

American College of Veterinary Dermatology Research Foundation Grant.

CONFLICT OF INTEREST STATEMENT

The authors have no conflicts of interest to declare.

Loek R, Gardiner D, Moore G, Marghoob A, Laporte C. Dermoscopic evaluation of normal canine skin with a handheld dermoscope. Vet Dermatol. 2025;36:593–601. 10.1111/vde.13368

DATA AVAILABILITY STATEMENT

The data that support the findings of this study are available from the corresponding author upon reasonable request.