DERMATOSCOPIC EVALUATION FOR DIFFERENTIATING PSORIASIS FROM SEBORRHOEIC DERMATITIS

Abstract

SUMMARY T he dermatoscope is a low-cost, noninvasive device that is readily available in daily clinical practice. Previously, dermatoscopy had been used in differentiating malignant pigmentary disorders, but the use of dermatoscopy has been extended to the diagnosis of non-pigmentary skin disorders by defining the characteristic vasculature. Psoriasis and seborrhoeic dermatitis are common erythematosquamous dermatoses that may present with scaly erythematous patches and plaques. Owing to the similar clinicopathological features of these dermatoses, their differentiation poses a diagnostic challenge. The purpose of this study was to evaluate the role of hand-held dermatoscopy in differentiating psoriasis from seborrheic dermatitis and to correlate these findings with the histopathological features. The current study included 40 patients; 20 patients with psoriasis; and 20 patients with seborrheic dermatitis. The diagnosis was confirmed in all patients based on the clinicopathologic features. We detected in our series a statistically significant lower mean age in seborrheic dermatitis cases than those with psoriasis. No statistically significant difference was detected between psoriasis and seborrheic dermatitis as regards gender of patients although seborrheic dermatitis was more common in males than in females. Additionally, we stated that a close relation exists between dermatoscopic patterns and the underlying histologic features. The red dots and globules represent the tortuous and dilated blood vessels within the elongated dermal papilla, and are the characteristic histologic features of psoriasis. On the other hand, the more prevalent arborizing vessels and atypical red vessels observed in our seborrheic dermatitis cases indicate markedly dilated capillaries in slightly hyperplastic rete ridges. In our series, we found that the most significant dermatoscopic vascular features of psoriasis were red dots and globules and glomerular vessels. In particular, several reports have described the peculiar dermatoscopic features of psoriasis, and red globules have been considered as the key diagnostic criterion for psoriasis. However, in our seborrheic dermatitis cases, there were; atypical red vessels, red dots globules and arborizing vessels. Atypical red vessels were observed in both diseases, but the frequency of this feature was higher in seborrhoeic dermatitis. In our study, silver-white scales were observed exclusively in psoriasis cases. Alternatively, greasy yellowish scales were observed exclusively in seborrheic dermatitis cases. Besides, erythematous background and structureless areas were detected in both diseases and were not considered as useful criteria for differentiation. We further investigated the difference between the dermatoscopic features among treated and untreated cases in the same disease. To our knowledge, this study is one of the limited studies comparing the effect of previous treatment on dermatoscopic features. In our series, arborizing vessels, atypical red vessels and twisted red loops presented only in untreated cases in both diseases. On the other hand, glomerular vessels as well as red dots and globules were found to be much decreased in treated cases than in untreated cases in both diseases.