Dotted vessels represent the most frequent dermoscopic feature of Psoriasis, being present in every single psoriatic plaque. Detection of any other morphologic type of vessels excludes the diagnosis of PP. The term “red globules” has also been used to describe the same dermoscopic feature.  Distinction between dots and globules is based on the diameter of the structure (dots are smaller), and it is important in dermoscopy of melanocytic tumors. In psoriasis, both terms may be used, since the roundish vascular structures can be of various diameters, although they are usually of similar size within a given lesion. Under higher magnifications (x100-x400), the psoriatic vessels appear as dilated, elongated, and convoluted capillaries. Histopathologically, red dots correspond to the loops of vertically arranged vessels within the elongated dermal papillae.
Important for differential diagnosis, the uniform distribution of the red dots within the lesion represents the dermoscopic hallmark of psoriasis. Dotted vessels may be detected in several inflammatory dermatoses, but no other disease exhibits the symmetrical and homogenous arrangement of vessels all over the lesion that characterizes psoriatic plaques, unless thick superficial scales cover them. Scales removal will bring to light the characteristic vascular pattern of psoriasis, possibly together with tiny red blood drops, which can be characterized as the dermoscopic “Auspitz sign”. A specific feature for the diagnosis of psoriasis is the sign of red globular rings, described by Vazquez-Lopez et al. If present, the red globules are arranged in irregular circles or rings. But even if highly specific, this sign is only seen in a minority of psoriatic lesions. Other types of vessels distribution are extremely rare in psoriasis. In addition, light red background color and white superficial scales are two common dermoscopic criteria of plaque psoriasis. In differential diagnosis of erythematosquamous dermatoses, scale color is of particular value: Yellow scales are a negative predictor of plaque psoriasis, therefore argueing for the presence of dermatitis.  Dermoscopic findings of psoriasis may vary dependent of the body site and the various amounts of scaling. In psoriatic balanitis and inverse psoriasis lesions that lack scaling, the regularly distributed red dots are prominent. Contrariwise, in scalp or palmoplantar psoriasis, thick hyperkeratotic plaques hide the typical vascular structures, which may be recognized after removal of the scales.
- Dermoscopic transformation of psoriatic plaques under treatment
Regular dermoscopic examination is of avail in patients under treatment with topical steroids or systemic biological agents, because additional morphologic information might be helpful for early detection of a relapse. Additionally, steroid-induced skin atrophy is earlier detected by dermoscopy (by revealing characteristic linear vessels) than in the clinical setting.
- Lallas et al.: Accuracy of dermoscopic criteria for the diagnosis of psoriasis, dermatitis, lichen planus and pityriasis rosea. Br. J. Dermatol. 2012;166:1198-205. PMID: 22296226. DOI.
- Vázquez-López et al.: Dermoscopic features of plaque psoriasis and lichen planus: new observations. Dermatology (Basel) 2003;207:151-6. PMID: 12920364. DOI.
- De Angelis et al.: Videocapillaroscopic findings in the microcirculation of the psoriatic plaque. Dermatology (Basel) 2002;204:236-9. PMID: 12037454. DOI.
- Vázquez-López et al.: A dermoscopy subpattern of plaque-type psoriasis: red globular rings. Arch Dermatol 2007;143:1612. PMID: 18087028. DOI.
- Kim et al.: Dermoscopy can be useful in differentiating scalp psoriasis from seborrhoeic dermatitis. Br. J. Dermatol. 2011;164:652-6. PMID: 21155753. DOI.
- Vázquez-López & Marghoob: Dermoscopic assessment of long-term topical therapies with potent steroids in chronic psoriasis. J. Am. Acad. Dermatol. 2004;51:811-3. PMID: 15523365. DOI.