*2.1.2 Dermoscopic differential diagnosis of plaque psoriasis*

Differential diagnosis of plaque psoriasis should be done with skin diseases, which are characterized by erythematous plaques with scales such as dermatitis, tinea corporis, pityriasis rosea, pityriasis rubra pilaris, lichen planus, and non-pigmented squamous cell carcinoma in situ.

In dermoscopic examination of dermatitis, we usually see patchy or scattered distributed dotted vessels with yellow globules (corresponding to sero-crusts) [10]. Background can be erythematous or not depending on lesions phase (acute or

#### **Figure 4.**

*Regularly distributed dotted vessels on reddish background with patchy distributed white scales. Note dot blood hemorrhages (red circle). Anatomical localization: Upper extremity (10).*

#### **Figure 5.**

*Background color can barely be seen due to diffuse thick white scales. Dotted vessels can be seen in the center. Note dot blood hemorrhages (red circle). Anatomical localization: Elbow (10).*

chronic). Hemorrhagic crusts can be seen as well secondary to traumatization (**Figure 7**).

In dermoscopic examination of tinea corporis, we usually see peripherally located dotted vessels and rough white scales (**Figure 8**). In contrast with psoriasis, dotted

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

**Figure 6.**

*a: Vessel distribution patterns (regular, scattered, in clusters, in rings, patchy, respectively). b: Vessels subtypes can be seen in higher magnifications (bushy, globular, radial, globular ring, hairpin, and comma vessels, respectively).*

#### **Figure 7.**

*Yellow globules, dot blood hemorrhages, and hemorrhagic crusts, patchy distributed dotted vessels (red circle). Background is slightly pinkish. Anatomical localization: Lower extremity (20).*

vessels are not regularly distributed and not uniform. In addition, scales are only located peripherally, tend to peel outward, and shaped in moth-eaten pattern [11].

Pityriasis rubra pilaris shows dotted and more frequently linear vessels, perifollicular yellow-orange halos, follicular plugs with central hair on them (**Figure 9**). Scales can be yellowish or whitish. Background is usually dark or yellowish red [7, 12].

Squamous cell carcinoma in situ and psoriasis can be challenging especially in solitary plaques. Dermoscopic clues for non-pigmented squamous cell carcinoma in situ are dotted or glomerular vessels in clusters in the center and arranged in lines at the periphery with yellowish white scales (**Figure 10**) [13, 14].

#### **Figure 8.**

*Peripherally located dotted vessels and white scales. Note the moth-eaten pattern (red circle). Anatomical localization: Trunk (10).*

#### **Figure 9.**

*Dotted vessels regularly distributed on pinkish background. Note the follicular plugs and central hairs (red circles). Anatomical localization: Elbow (20).*

Dermoscopic features of plaque psoriasis and its differentials are summarized in **Table 1**.
