**Figure 12.**

*Regularly distributed dotted vessels in reddish background. White scales. Anatomical localization: Upper extremity (10).*

*Dermoscopic Differential Diagnosis of Psoriasis DOI: http://dx.doi.org/10.5772/intechopen.103004*

#### **Figure 13.**

*Regularly distributed dotted vessels on pinkish background. Scales are white, thin, and patchy. Anatomical localization: Upper extremity (10).*

#### *2.2.2 Dermoscopic differential diagnosis of guttate psoriasis*

Differential diagnosis of guttate psoriasis should be done with skin diseases, which are characterized by erythematous papules/small plaques with scales. Pityriasis rosea, lichen planus, nummular dermatitis, secondary syphilis, tinea corporis, pityriasis lichenoides chronica, and disseminated eruptive porokeratosis may count as differential. (Dermatitis and tinea corporis will not be mentioned because they were discussed above.)

Dermoscopic examination of pityriasis rosea shows irregular distributed dotted vessels and peripheral thin white scale (**Figure 14**) [10]. Scales tend to peel outward as in tinea corporis. But note the white scale is not rough and vessels are not in the same distribution with scales. Background is generally skin-colored or slightly pinkish.

In dermoscopic examination of lichen planus, key point is detecting Wichkam striaes, which cannot be seen macroscopically sometimes. In fair-skinned patients,

#### **Figure 14.**

*Patchy distributed dotted vessels and peripheral thin white scale. The configuration of the scales named "collarette sign." anatomical localization: Back (10).*

dotted and linear vessels around Wickham striae make these structures more visible (**Figure 15**); however, in dark-skinned patients, absence of peripheral vascular structures around Wichkam striaes may lead to misdiagnosis [16].

In dermoscopic examination of secondary syphilis, yellowish-orange background and absence of vascular structures are key points (**Figure 16**) [17]. Scales may be present, however, thinner and smaller when compared with psoriatic scales.

In dermoscopic examination of pityriasis lichenoides chronica, we usually see orange-yellowish structureless areas and focally distributed dotted or linear vessels (**Figure 17**) [18].

#### **Figure 15.**

*Reticular arranged white lines (Wickham striae). Note the dotted vessels around Wickham striae in this fair-skinned patient. Anatomical localization: Lower extremity (10).*

#### **Figure 16.**

*Yellowish-orange structureless area with thin white scales. Note the absence of vascular structures. Anatomical localization: Back (10).*

*Dermoscopic Differential Diagnosis of Psoriasis DOI: http://dx.doi.org/10.5772/intechopen.103004*

#### **Figure 17.**

*Yellowish-orange structureless areas with thin white scales. Note the focal dotted vessel areas (red circles). Anatomical localization: Hand dorsum (10).*

#### **Figure 18.**

*Small white scales on yellowish-brown background. Note the railway-like "cornoid lamella" at the periphery (red arrows). Anatomical localization: Hand dorsum (10).*

In dermoscopic examination of porokeratosis, key clue is peripheral double lines resembling railways (**Figure 18**). This feature is called "cornoid lamella" [19].

Dermoscopic features of guttate psoriasis and its differentials are summarized in **Table 2**.

#### **2.3 Inverse psoriasis**

Inverse psoriasis is another clinical variant of psoriasis, which involves flexural areas such as axillary, inguinal, and inframammary [20]. The prevalence of inverse psoriasis is not clear and varies in 3–36% because of diagnostic challenges [21]. And also it is controversial that if genital involvement is a part of inverse psoriasis; however, we include genital involvement under this topic for convenience of expression.


**Table 2.**

*Dermoscopic features of guttate psoriasis and its differentials.*

*a: Erythematous plaque located in inframammary fold. b: Erythematous papules and plaques located in axillary fold. Note peripheral lesions have mild white scales.*

Inverse psoriasis is typically present with well-defined erythematous plaques located in flexural areas (**Figure 19a** and **b**). It can present with or without typical psoriasis plaques. In contrast with plaque and guttate psoriasis, scales are insignificant or absent.
