Diagnosing and differentiating pityriasis rubra pilaris (PRP) from other disorders can be a challenging task. Although histopathology remains the gold standard, it may not be feasible at times, especially in children.

Overall, our results suggest that dermoscopy might be particularly useful to discriminate between PRP and psoriasis, at least in an Indian population, since the dermoscopic patterns of the 2 entities are clearly different.

Of note, yellow color, which was in our study and previous studies one of the consistent findings of PRP, has been suggested as a potent negative predictive factor for the diagnosis of psoriasis. A previous study investigated the accuracy of dermoscopic criteria for the differentiation of psoriasis from other inflammatory diseases.

Dermoscopic criteria

As per the latter study, the presence of regularly distributed dotted vessels is very highly suggestive of psoriasis over any other diagnosis. Although the latter study did not include PRP in the control group, the results and previous results on dermoscopy of PRP suggest that the same conclusion is very likely to be valid for the differential diagnosis between psoriasis and PRP.

In addition, the latter study suggested yellow color as a potent negative predictive factor for the diagnosis of psoriasis. In the present and previous studies, yellow color was one of the most consistent findings of PRP, supporting further that dermoscopy is useful for the differential diagnosis between PRP and psoriasis.

Previous reports investigated also the dermoscopic findings in peculiar subtypes of PRP. Specifically, erythrodermic PRP was suggested to dermoscopically display orange blotches and islands of non-erythematous (spared) skin displaying reticular vessels. In contrast, erythrodermic psoriasis is typified by diffusely distributed whitish scales and regularly arranged dotted/glomerular vessels.

Keratoderma resulting from PRP has been suggested to display structureless orange areas of different sizes in a patchy distribution along with the white scale. Dermoscopy of juvenile PRP also shows multiple whitish keratotic follicular plugs and a yellowish peripheral keratotic ring surrounded by erythema with some linear vessels.

The sample did not include patients with these peculiar forms of PRP, so the latter evidence cannot be assessed by the present study. Round-to-oval yellowish areas surrounding a central hair with or without follicular plugs represent the most frequent dermoscopic pattern of PRP.

In contrast, psoriasis is typified by numerous and regularly distributed dotted vessels and white scales. This information might aid clinicians to differentiate atypical cases of PRP from psoriasis.