Psoriasis
Authors: Annie Price, Saumya Singh
Chief Editor: Dr Daniel Keith
Psoriasis is a chronic inflammatory skin condition. There are several clinical subtypes responsible for varying phenotypes and histopathological findings. Whilst histopathological investigation is considered gold standard, the mainstay of diagnosis is made through careful clinical history and examination. As such, dermoscopy offers a useful and accessible diagnostic adjunct.
Macroscopic Appearance
An example of a psoriatic plaque: a well-demarcated area of scale on an indurated, erythematous background.
Example in Fitzpatrick Skin Type 3
A well-demarcated area of silvery scale with multiple erythematous, satellite plaques.
Example in Fitzpatrick Skin Type 2
Multiple coalesced, annular plaques with white scale. Several areas of hypopigmentation can be appreciated.
Example in Fitzpatrick Skin Type 5
Dermoscopic Appearance
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Scale is the hallmark sign of plaque psoriasis and is classically described in terms of colour (typically white) and distribution.
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Dotted vessels are also a characteristic dermoscopic feature of plaque psoriasis. They are arranged in symmetrical and regular patterns: it is the homogenous distribution of these vessels which is unique to psoriasis and differentiates it from other inflammatory skin disorders.
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Auspitz sign is characterised by punctate bleeding points. Dermal capillaries rupture in response to minimal trauma of the overlying hyperkeratosis. If underlying structures are obstructed by diffuse plaque, it may be appropriate to first remove some scale to reveal the bleeding papillaries. This phenomenon is referred to as dermoscopic Auspitz’s sign.
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Globular ring is where a ring shape is made up of dotted vessels.
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Signet ring sign and hidden hair seen in scalp psoriasis (not seen in the examples below).
Illustration courtesy of Dr Lizzy Wasson
This annotated example illustrates the following features:
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Auspitz sign (black arrows)
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Globular ring (yellow arrow)
This image shows white scale on an erythematous background. Circular and oval dotted capillaries can be seen in the centre of the plaque (yellow arrow) and hairpin dotted capillaries are visible at the peripheries (black arrow)
This is an unannotated version of the same image on the left, for comparison.
Diffuse white scale on an erythematous background
A further example of white scale in Fitzpatrick Skin Type 5.
Rossettes in Psoriasis
Rosettes can occasionally be observed in psoriasis, although they were initially thought to be specific to conditions such as actinic keratosis and squamous cell carcinoma. They appear as shiny white structures, visible under polarised light, along with shiny white lines and areas lacking clear structure. Over time, it has been recognised that rosettes can also appear in a variety of other inflammatory, infectious, and proliferative conditions. There are two types of rosettes: small rosettes (0.1–0.2 mm) and large rosettes (0.3–0.5 mm).
Macroscopic appearance:
Psoriatic plaques are mostly covered with white scales, though they can also have white-yellowish, yellowish, or blue-gray scales, and these scales are often spread out across the plaque. The background of the psoriatic papule can vary in shades of pink and red.
Macroscopic appearance on the dorsum of a patients hand
Erythematous plaque with whitish scales
Dermoscopic Features:
In plaque psoriasis, dermoscopy under polarised light typically shows regularly arranged dotted blood vessels on a pink background, a white network-like pattern, and widely spread whitish scales. The most common vascular feature in psoriasis is red dots or globules, which are usually arranged in a regular pattern.
Dermoscopy under polarised mode showing whitish scales (red arrow) and small white rosette (blue arrow).