Dermoscopic Differential Diagnosis of Psoriasis

Abstract

Psoriasis is a chronic inflammatory skin disease, which is mainly characterized with erythematous indurated plaques with squams such as many other inflammatory skin diseases. Also different clinical subtypes of psoriasis can show distinctive clinical appearances. As an example, inverse psoriasis does not have squams and resemble erythema intertrigo; or erythrodermic variant cannot be distinguished from other erythroderma causes sometimes. From reasons above, differential diagnosis of psoriasis should be done carefully to manage a chronic and long-term treatment required disease appropriately. Histopathologial examination is gold standard technique for certain diagnosis; however, dermoscope is a noninvasive and easily applicable diagnostic tool with high specificity. In this chapter, we discuss dermoscopic differential diagnosis of psoriasis.

1. Introduction

Psoriasis is a chronic inflammatory skin disease that progresses with remission and exacerbations [1, 2]. It constitutes an important percentage, approximately 6–8% of patients who apply to dermatology clinics [3]. Due to its high prevalence and chronic course, it is important to diagnose it early and clearly to manage patient appropriately and avoid functional losses as much as possible. In addition, in some situations that should be intervened swiftly such as erythrodermic psoriasis or generalized pustular psoriasis; the sooner we diagnose, the better we take control of disease setting.

In diagnosis of psoriasis, usually clinical observation is enough; however, in doubtful cases, histopathological examination is required as gold standard technique. However, it requires an invasive procedure and needs time for pathological preparation. With dermoscopy, we can mostly distinguish psoriasis from other resembling diseases in clinic noninvasively. Despite it not being gold standard, easily applicable and noninvasive properties of dermoscopy make it a helpful diagnostic tool and reduce the need of performing biopsies.

2. Dermoscopy of psoriasis types and differentials

2.1 Plaque psoriasis

Plaque psoriasis is the most common clinical subtype of psoriasis with 90% of all cases [4]. It is characterized by erythematous, well-defined, and usually indurated plaques greater than 1 cm in size with white-silvery scales on them (Figure 1). They can vary in size and may coalesce. Especially rapidly progressing lesions can be seen in annular configuration (Figure 2) [4, 5]. Removal of psoriatic scales may cause pinpoint bleedings, which is called Auspitz sign. Psoriatic plaques are mostly located in the scalp, trunk, lumbosacral area, and extensor surfaces of extremities (Figure 3) [6].

Figure 1.

Erythematous, well-defined indurated plaque with white scales.

Figure 2.

Erythematous, annular plaques with white scales.

Figure 3.

Psoriatic plaques located on the trunk and extensor surfaces of the arms.

2.1.1 Dermoscopy of plaque psoriasis

Dermoscopic examination of a psoriasis plaque should be done in three categories: background, vessels, and scales. Examination should be done with minimal pressure to visualize vessels better and with immersion oil if possible.

In dermoscopic examination of plaque psoriasis with handheld dermoscope, we usually see regularly distributed dotted vessels in a reddish-pinkish background and white scales (Figure 4) [7]. In some cases, background can be grayish-white due to highly hyperkeratotic scales (Figure 5).

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).

Apart from regular distribution, vessels can be distributed scattered, in clusters, in rings, and patchy (Figure 6a). In higher magnifications (with videodermoscopy), these dotted vessels can be seen as bushy capillaries, globules, radial capillaries, globular rings, hairpin capillaries, and comma vessels in descending order [8] (Figure 6b). Rarely dot blood hemorrhages can be seen in vessel locations (Figure 5). Scales can be distributed diffuse, patchy, central, or peripheral in descending order; however, white color is key point for scales [8, 9].

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).

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

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).

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

Figure 8.

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

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].

Figure 9.

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

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 10.

Glomerular vessels in the center, white scales. Note the linear arrangement of dotted vessels at the periphery (red circles) and actinic keratosis area at top left. Anatomical localization: Forearm (×20).

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

	Background	Vessel types	Vessel arrangement	Scales	Additional features
Plaque psoriasis	Reddish-pinkish; Whitish (due to hyperkeratotic scales)	Dotted	Regular	Whitish-grayish
Dermatitis	Skin colored-pinkish	Dotted	Scattered/patchy	Yellowish	Irregularly distributed dot blood hemorrhages due to traumatization
Tinea corporis	Reddish	Dotted	Peripheral	White and rough; peripheral; moth-eaten pattern; tend to peel outwards
Pityriasis rubra pilaris	Dark red/yellowish red	Linear and/or dotted	Scattered	Yellowish-whitish; follicular	Perifollicular yellow-orange halos, follicular plugs, central hair
Squamous cell carcinoma in situ	Pinkish	Glomerular or dotted	Regularly in center, may organize in lines at the periphery	Yellowish white scales	Peripheral actinic keratosis areas may help (white and wide follicular openings, rosettes)

Table 1.

Dermoscopic features of plaque psoriasis and its differentials.

2.2 Guttate psoriasis

Guttate psoriasis, a psoriasis variant that is more common in pediatric population and young adults. Distinctly from other variants, we know that guttate psoriasis is selectively triggered by beta hemolytic streptococcal infections [15]. It is characterized by erythematous, well-defined flat papules/plaques lower than 1 cm in size with white-silvery scales on them. Lesions mostly located in the trunk and extremities (Figure 11a and b).

Figure 11.

a: Slightly erythematous flat papules/plaques with white scales on them in an adolescent. Trunk localization. b: Slightly erythematous flat papules/plaques with white scales on them in an adolescent. Extremity localization.

2.2.1 Dermoscopy of guttate psoriasis

Dermoscopic features of guttate psoriasis are very similar with plaque psoriasis, which is characterized by regularly distributed dotted vessels in a reddish background and white scales on them (Figure 12). Due to guttate psoriasis’ smaller lesion sizes (lower than 1 cm in diameter), findings may be insignificant when compared with plaque psoriasis (Figure 13).

Figure 12.

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

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.

Figure 14.

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

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

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).

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.

Figure 16.

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

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 17.

Yellowish-orange structureless areas with thin white scales. Note the focal dotted vessel areas (red circles). 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].

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).

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

	Background	Vessel types	Vessel arrangement	Scales	Additional features
Guttate psoriasis	Reddish-pinkish	Dotted	Regular	Whitish-grayish, thin and small
Pityriasis rosea	Pinkish	Dotted (vascularization is not dominant)	Patchy	White, thin, peripheral and tend to peel outwards “collarette sign”
Lichen planus	Pinkish, violaceus	Dotted or absent	Aroud Wickham striae	Whitish, patchy distributed, thin and small
Secondary Syphilis	Yellowish-orange	Absent		White and thin
Pityriasis lichenoides chronica	Pinkish, yellowish-orange	Dotted or linear	Focal	White, patchy, thin
Disseminated porokeratosis	Yellowish-brown	Unsignificant		White, small	Peripheral railway like double lines called “cornoid lamella”

Table 2.

Dermoscopic features of guttate psoriasis and its differentials.

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.

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.

Figure 19.

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

Genital involvement shares similar clinical features with inverse psoriasis such as well-defined erythematous papules and plaques (Figure 20). However, occlusion in the genital areas is not as much as flexural areas, scales could be more visible in the genitals.

Figure 20.

Coalesced erythematous papules located in the glans penis and penile dorsum.

2.3.1 Dermoscopy of inverse psoriasis

Dermoscopic features of inverse psoriasis are characterized by regularly distributed dotted vessels on reddish background (Figure 21). In contrast with other variants, scales are absent. Absence of scales enhances visualization of vascular structures. Consequently, dermoscopic differential diagnosis of flexural dermatosis mainly leans on evaluation of vascular structures.

Figure 21.

Regularly distributed dotted vessels on pinkish background. Anatomical localization: Inframammary (×10).

2.3.2 Dermoscopic differential diagnosis of inverse psoriasis

Differential diagnosis of inverse psoriasis should be done with skin diseases, which present with erythematous patches/plaques in flexural and genital areas. Mechanical intertrigo, seborrheic dermatitis, lichen planus inversus, and fungal/bacterial infections may count as differential. Because no clear dermoscopic features have been defined for mechanical intertrigo and flexural infections, we will discuss dermoscopic features of seborrheic dermatitis and lichen planus inversus under this topic.

The main dermoscopic features of seborrheic dermatitis of flexural areas are irregularly distributed linear, blurry vessels [22]. As we mentioned before, we do not see classical yellowish scales of seborrheic dermatitis in flexuras.

When we review the literature so far, there are only three reports about dermoscopic features of lichen planus inversus. In all of these reports, dermoscopic features of only pigmented variant of lichen planus inversus were evaluated and defined as diffuse brown patches containing multiple granular gray-brown dots [23, 24, 25]. In our clinical practice, we see non-pigmented lichen planus inversus more than pigmented subtype. According to our dermoscopic experience, Wickham striae, which is seen in lichen planus inversus, tends to be in “starry sky” or “radial streaming” pattern rather than reticular pattern. Background is usually pinkish or violaceous. Dotted vessels usually encircle Wickham striae (Figure 22).

Figure 22.

Wickham striae in “radial streaming” pattern (red circle) and “starry sky” pattern (blue circle). Dotted vessels surround Wickham striae in a patchy arrangement. Anatomical localization: Intermammary (×10).

Dermoscopic features of inverse psoriasis and its differentials are summarized in Table 3.

	Background	Vessel types	Vessel arrangement	Additional features
Inverse psoriasis	Reddish-pinkish	Dotted	Regular
Seborrheic dermatitis of flexural areas	Pinkish	Linear, blurry vessels	Irregular
Lichen planus inversus	Pinkish, violaceus	Dotted or absent	Aroud Wickham striae	According to our dermoscopic experience, Wickham striae, which is seen in lichen planus inversus, tends to be in “starry sky” or “radial streaming” pattern

Table 3.

Dermoscopic features of inverse psoriasis and its differentials.

2.4 Pustular psoriasis

Pustular psoriasis is a rare clinical variant of psoriasis, which is characterized by sterile pustules on an erythematous skin (Figure 23). It could be either local or generalized [26]. In generalized pustular psoriasis, concomitant fever, malaise, dehydration may also be present [27].

Figure 23.

Small pustules and lake of pus on erythematous background.

2.4.1 Dermoscopy of pustular psoriasis

Dermoscopic features of pustular psoriasis are characterized by regularly distributed dotted vessels with milky globules (corresponding to sterile pustules) on reddish background (Figure 24) [28]. Attention should be paid on non-follicular localization of pustules. Typical vascular structures are seen. Nonspecific yellow crust may be seen. Dermoscopic features are same in both localized and generalized subtypes.

Figure 24.

Milky globules and regularly distributed dotted and bushy vessels on reddish background in pustular psoriasis. Anatomical localization: Trunk (×10).

2.4.2 Dermoscopic differential diagnosis of pustular psoriasis

Dermoscopic differential diagnosis of pustular psoriasis should be done with acute generalized exanthematous pustulosis (AGEP). In life-threatening clinical conditions such as generalized pustular eruptions, rapid and right diagnosis is essential, and dermoscope is very helpful at that point. In both pustular psoriasis and AGEP, pustules are sterile, disseminated, may coalesce, and be non-follicular. Thereby, we cannot distinguish these two situations by their clinical view only. In dermoscopic examination of both pustular psoriasis and AGEP, non-follicular milky globules on reddish background are seen [28]. Discriminately, in pustular psoriasis we see regularly distributed dotted vessels (Figure 24). In dermoscopic examination of AGEP, background is usually pinkish and vascular structures are absent (Figure 25) [29].

Figure 25.

Milky globules on reddish background. Globules are non-follicular (red circle). Note the absence of vessels. Anatomical localization: Trunk (×10).

2.5 Erythrodermic psoriasis

Erythroderma is a life-threatening condition, which is defined as desquamation and erythema of more than 90% of body surface area [30]. Erythrodermic variant of psoriasis (Figure 26) generally occurs due to poor control of disease, withdrawal of anti-psoriatic treatments, triggering drug intake, underlying systemic infections or conditions [31]. Clinical clues for erythrodermic psoriasis diagnosis are known history of psoriasis, psoriatic nail changes, presence of psoriatic arthritis. However, if none of the mentioned features is present, dermoscopy could be a game-changer.

Figure 26.

Desquamation and erythema of all body surfaces.

2.5.1 Dermoscopy of erythrodermic psoriasis

Dermoscopic features of erythrodermic psoriasis are the same as other psoriasis variants. Regularly distributed dotted vessels on a reddish background, and patchy white scales are seen (Figure 27) [32].

Figure 27.

Regularly distributed dotted vessels and white scales. Anatomical localization: Lower extremity (×20).

2.5.2 Dermoscopic differential diagnosis of erythrodermic psoriasis

Dermoscopic differential diagnosis of erythrodermic psoriasis includes dermatosis that can present with erythroderma such as atopic dermatitis, mycosis fungoides, and pityriasis rubra pilaris (Pityriasis rubra pilaris will not be mentioned because it was discussed above.)

Dermoscopic examination of atopic dermatitis shows typical dermatitis features. Yellowish globules (corresponding to sero-crusts) and patchy distributed dotted vessels on a pinkish background are demonstrative (Figure 28) [32].

Figure 28.

Yellow globules, patchy distributed dotted vessels. Background is slightly pinkish. Tiny white scales are also present. Tiny white scales correspond to desquamation areas. Anatomical localization: Trunk (×10).

Dermoscopic features of erythrodermic mycosis fungoides are a combination of linear and dotted vessels on a pale pinkish background (Figure 29) [32]. Some short linear vessels may be curved and named as “spermatozoon-like” vessels.

Figure 29.

Linear, serpiginous, and dotted vessels on pinkish background. Tiny white scales correspond to desquamation areas. Anatomical localization: Trunk (×10).

Dermoscopic features of erythrodermic psoriasis and its differentials are summarized in Table 4.

	Background	Vessel types	Vessel arrangement	Scales	Additional features
Erythrodermic psoriasis	Reddish	Dotted	Regular	White, scattered-patchy scales
Erythrodermic atopic dermatitis	Pinkish	Dotted	Patchy	Yellowish sero-crusts
Erythrodermic mycosis fungoides	Pinkish (pale)	Linear and dotted	Scattered	Whitish scales can present.	.

Table 4.

Dermoscopic features of erythrodermic psoriasis and its differentials.

3. Conclusions

Psoriasis is a common skin disease with different clinical presentations. Generally, clinical evaluation is enough for diagnosis, though dermoscope is a helpful and noninvasive examination technique that enhances true diagnosis ratio. Knowing psoriasis’ and its differentials’ dermoscopic features may reduce requirement for histopathological examination and also makes rapid diagnosis possible in life-threatening conditions such as erythroderma. Note that regularly distributed dotted vessels on a reddish background are the most important clues for any variant of psoriasis. In doubtful cases, histopathological examination should be done for verifying the diagnosis as a gold standard technique.

Acknowledgments

All photos used in this chapter were taken by Dr. Ece Gokyayla with iPhone (XS) and dermatoscope (DermLite, DL4 model, 3Gen, USA) connected to an iPhone (XS) via adapter (DermLite Connection Kit MagnetiConnect). Immersion oil was not used. Written informed consent will be obtained from each patient in oral and written form. Only histopathologically or laboratorially confirmed cases’ photographs were included.

Conflict of interest

The authors declare no conflict of interest and no funding source.