Dermoscopy as a diagnostic tool in Psoriasis

Received 15 August 2020 Revised 29 September 2020 Accepted 30 September 2020 Online 10 January 2021 Print 31 January 2021 Dermoscopy allows visualizing vascular and non-vascular structures and aids in making an accurate diagnosis of pathological skin lesions. The aim of the present study was to observe and report the dermoscopic patterns of psoriatic lesions and correlate the dermoscopic diagnosis with the clinico-histopathological diagnosis. This was a prospective, observational study conducted over a period of 18 months in 44 patients who presented with psoriasis to the outpatient clinic of our department. Psoriatic skin lesions were evaluated clinically and subjected to dermoscopy and histopathological examination and the resulting diagnoses were correlated to establish the diagnostic utility of dermoscopy in psoriasis. The resultant findings were predominantly vascular i.e. red globules (RG-75%), glomerular like vessels (GLV22.72%), red dots (RD-2.27%), in regular distribution (100%) and the non-vascular findings were white scales (93.18%) in a diffuse arrangement (79.54%) and a light red background (56.18%). A combination of these vascular and non-vascular features predicted psoriasis accurately and was found to be significant. A positive correlation between the clinico-dermoscopic-histopathological diagnosis was possible in 75% of the cases. In conclusion, dermoscopic examination is a good auxiliary to strengthen the clinical diagnosis of psoriasis and may help evade the necessity of a biopsy on further standardization of the dermoscopic features in literature. Corresponding author

Dermoscopy allows visualizing vascular and non-vascular structures and aids in making an accurate diagnosis of pathological skin lesions. The aim of the present study was to observe and report the dermoscopic patterns of psoriatic lesions and correlate the dermoscopic diagnosis with the clinico-histopathological diagnosis. This was a prospective, observational study conducted over a period of 18 months in 44 patients who presented with psoriasis to the outpatient clinic of our department. Psoriatic skin lesions were evaluated clinically and subjected to dermoscopy and histopathological examination and the resulting diagnoses were correlated to establish the diagnostic utility of dermoscopy in psoriasis. The resultant findings were predominantly vascular i.e. red globules (RG-75%), glomerular like vessels (GLV-22.72%), red dots (RD-2.27%), in regular distribution (100%) and the non-vascular findings were white scales (93.18%) in a diffuse arrangement (79.54%) and a light red background (56.18%). A combination of these vascular and non-vascular features predicted psoriasis accurately and was found to be significant. A positive correlation between the clinico-dermoscopic-histopathological diagnosis was possible in 75% of the cases. In conclusion, dermoscopic examination is a good auxiliary to strengthen the clinical diagnosis of psoriasis and may help evade the necessity of a biopsy on further standardization of the dermoscopic features in literature. ture as multiple, salmon pink to erythematous, papules and plaques associated with easily removable micaceous scales 3 . Although histopathology remains the undisputed gold standard diagnostic test for psoriasis, it is an invasive procedure. Therefore, further efforts are warranted to substantiate the clinical diagnosis non-invasively. Dermoscopy has an established value in evaluation of skin tumours and is gaining growing interest regarding its application in the field of general dermatology especially in inflammatory conditions like psoriasis, where the features noted are representative of the underlying microscopic pathology [4][5][6] .

Material and methods
This is a prospective, observational study conducted over a period of 18 months in 44 patients with psoriatic skin lesions who attended the outpatient clinic of the Department of DVL in our institute. Patients were selected by the convenience sampling method. Patients who have used topical or systemic medications for a period of ≥1month, undergone any invasive procedure over the lesions, secondarily infected lesions or debilitating conditions were excluded from the study. Informed written consent of participating patients was taken and necessary demographics were noted. A detailed clinical history and examination aided in a clinical diagnosis of psoriasis, based on standard definitions and features known as per the literature. The clinical photographs of the lesions were captured with a digital camera. A videodermoscope (Ultracam TLS, Dermaindia) equipped with providing a high optical magnification, three light sources (white light, polarized light, ultraviolet light) and an inbuilt camera was used to evaluate the lesions. The dermoscopic screening of the lesions was carried out according to a systematic approach specified by Zalaudek et al 7 , which takes into consideration the number of lesions, vascular morphology, arrangement of the vasculature and other salient dermoscopic features, all of which aid in reaching a diagnosis. Images of these findings were captured and stored in the system along with patient details for future reference. Then a 4-5mm punch biopsy of the lesion was done under local anesthesia and sent for histopathological examination (HPE). Hematoxylin and Eosin (H&E) staining was done, and histopathological features were noted. The clinical and dermoscopic findings were compared and contrasted with the histopathological features and a conclusive diagnosis was reached. All the data obtained was tabulated and statistically analyzed at the end of the study using SPSS version 20.0, to obtain valid conclusions. Continuous vari-ables are presented as mean ± SD and discrete variables are shown as percentages.

Discussion
Psoriasis is a relatively common papulosquamous disorder which bears clinical overlap with other inflammatory conditions like pityriasis rosea, dermatitis, lichen planus, etc. Histopathology helps in the definitive diagnosis of these conditions but is invasive and may not always be feasible to perform. Dermoscopy is a suitable alternative for this purpose and shows characteristic combination of features in different diseases 4 . In our study, on dermoscopy, scaling was seen in all the cases (100%) and silvery white scales were observed in 93.18% with a diffuse distribution (79.54%). Atypi-cal features like white+yellow scales (6.81%), patchy (15.9%) and peripheral (4.54%) distribution of scales were seen in a relative minority. Surface features like scale morphology were better visible in the white light mode and the vascular features like vessel morphology, background color were better appreciated with the polarized light. Lallas et al 8 studied 139 lesions in 85 patients with psoriasis and found that while the vascular features were the same in all variants, the frequency of white scales varied according to the different body sites. They noted that white scales were detected in all scalp and palmo-plantar lesions, while flexural and genital psoriasis showed little to no scaling. A similar pattern was noticed in our patients, with patchy, white, minimal scales in flexural psoriasis, more hyperkeratotic scales in palmoplantar psoriasis and diffuse, white scaling in rest of the variants. Background color is also an important feature to consider while making a dermoscopic diagnosis. In this series, different background colors were noted (as shown in table 4) in psoriasis patients of which 56.81% showed a light-red background and 40.9% showed a dull red background. Lallas et al 4 noted the background colors of light red in 41% and dull red in 58% cases in their study, while Pan et al 9 found a predominance of light red color (78%). Grey blue background was found in a single case in our study (i.e. in the elephantine variety); this observation was previously noted only by Chandravathi et al 10 .
As stated earlier, the dermoscopic vascular findings observed in this study were Red globules/RG (75%), Glomerular Like Vessels/GLV (22.72%) and Red dots/RD (2.27%)arranged in a homogenous regular pattern in 100% cases. 20 (68.96%) of the 29 plaque psoriasis cases showed RG and 9 (31.03%) showed GLV. 80% of guttate psoriasis cases showed RG, while remaining 20% revealed GLV. 100% of scalp, flexural, erythrodermic and elephantine psoriasis cases showed RG. RD was seen only in a single case (33.33%) and RG in 66.66% cases of palmoplantar psoriasis.    4 noted that most cases of plaque psoriasis showed red dots, which were distributed regularly. They concluded that the combination of regularly distributed dotted vessels over a light red background along with diffuse white scales was highly predictive of psoriasis and that deviation from these findings significantly decreased the probability of a diagnosis of psoriasis 4 . In our study, we did not see red dots in a significant number of cases; instead there was a predominance of red globules followed by glomerular like vessels. In the studies by Vasquez-Lopez et al 11 and Chandravathi et al 10 RG, GLV in homogenous distribution were the predominant vascular findings. Musumeci et al 12 described videodermoscopic findings in psoriasis and noted the presence of dilated capillaries with a bushy aspect distributed homogenously throughout the lesions. As the magnification of the device increases the diameter of the vessels appears more and shows the tortuosity of the vessels. The variations observed in different studies may be attributable to the use of different models of dermoscope / videodermoscope which provide variable magnifications. Dilated vessels on dermoscopy are not a standalone feature suggestive of psoriasis as they may occur in other inflammatory and neoplastic disorders. Therefore, they must be assessed in combination with vascular arrangement and other non-vascular findings 4 . In the present study, a combination of dermoscopic features, i.e. Red globules (RG) and glomerular like vessels (GLV) in a regular arrangement over a light red background, along with white scales in a diffuse distribution were found to be significant.
Once a clinico-dermoscopic diagnosis was made, biopsy was performed where feasible. Of the 37 patients (84.09%) in whom biopsy could be done, histopathology was suggestive of psoriasis in 33 (89.18%) cases. Remaining 4 (10.81%) cases showed psoriasiform / non-specific features. The most common histological features observed in classical cases of psoriasis were hyperkeratosis, parakeratosis, decreased or absent granular layer, dilated blood vessels, supra papillary thinning, neutrophil abscesses, elongation of rete ridges. This was comparable to the findings of a study conducted by Gordon and Johnson 13 . Dermoscopic features seen can be explained by these underlying microscopic histopathological changes in psoriatic skin. A positive clinico-dermoscopichistopathological correlation was seen in 75% cases of psoriasis. In 15.9% cases biopsy could not be done as patients were either not willing or not suitable for the procedure. There was a clinicodermoscopic-histological dissonance in only 10.81% cases. However, dilated capillaries and hyperkeratosis were seen on histopathological examination, in 97.29% and 75.67% cases respectively which explains the positive clinicodermoscopic correlation seen despite a nonspecific histopathological diagnosis, since dilated capillaries in regular arrangement and diffuse white scales are major dermoscopic criteria for psoriasis.
In this study, dermoscopic assessment was done by a single observer with no appraisal of inter observer reproducibility, biopsy could not be done in all patients, not all variants of psoriasis were included. These limitations should be addressed in future studies.

Conclusion
Though histopathology remains the gold standard diagnostic test for psoriasis, based on the observations noted in the present study, it may be concluded that dermoscopy is a feasible, non-invasive test which provides another level of morphology between the macroscopic clinical and microscopic histopathological features. Further standardization of the relevant dermoscopic criteria in psoriasis may obliviate the need for invasive procedures.

Declaration of patient consent:
The authors certify that they have obtained appropriate consent forms in which the patients have given consent for their images and other relevant clinical information to be reported in the journal, with the understanding that their names or initials will not be published, and proper efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Conflicts of interest:
There are no conflicts of interest.