MedWire News: Scalp psoriasis and seborrheic dermatitis can be differentiated by looking at vascular patterns using dermoscopy, report researchers.

It can be hard to discriminate between the two conditions as they have very similar clinicopathological features, says the team. Both can occur on the scalp and it is particularly difficult to diagnose psoriasis or seborrheic dermatitis for isolated lesions in this area.

Byung-Soo Kim (Pusan National University, Busan, Korea) and colleagues carried out a retrospective observational study of 55 patients with scalp psoriasis and 41 patients with seborrheic dermatitis, aged 40.8 years on average, to assess the usefulness of dermoscopy for clinical differentiation. The patients were recruited from two Korean teaching hospitals.

"Previously, dermoscopy had been used in differentiating malignant pigmentary disorders, but recently, the use of dermoscopy has extended to the diagnosis of nonpigmentary skin disorders by defining the characteristic vasculatures," they explain.

Writing in the British Journal of Dermatology, Kim and co-workers report that the most notable scalp psoriasis features under dermsocopy were red dots and globules, twisted red loops, and glomerular vessels.

Seborrheic dermatitis, in contrast, was characterized by the presence of arborizing vessels and atypical red vessels, as well as featureless areas with no particular vascular pattern, but had no red dots and globules.

As atypical red vessels were commonly observed in both conditions, this was not considered to be a useful diagnostic feature.

"This study clearly shows that dermoscopy is a valuable non-invasive tool for differentiating scalp psoriasis and seborrheic dermatitis, and it can also reduce the frequency of unnecessary skin biopsies," conclude the authors.

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