Dermoscopy in Psoriasis can be very useful – because it displays repetitive features.
Dermoscopic features of Psoriasis:
- Uniformity distributed dotted red vessels which histopathologically corresponds to the dilated capillaries found in the elongated dermal papillae
- A light/dull red background
- Diffuse white scaling ( histologically corresponding to parakeratosis.
These 3 features combined has good diagnostic accuracy
- The blood vessels in psoriasis are typically similar in size and shape and are distributed at uniform distance from each other
- But in the hyperkeratotic lesions – these vessel morphology cannot be appreciated – so on removing the scales we can see tiny bleeding points – this is referred to as “Dermoscopic auspitz sign)
The red dots can also be arranged in – patchy/clustered/ring form
Sometimes the vessels can be seen as red globules (vessels with diameter >0.1mm) and these globules are common in the leg (because of increased hydrostatic pressure)
- Dotted vessels and diffuse white scaling – also seen in Bowen’s disease – but vessels here are distributed in focal/clustered pattern and are also different in size, shape and distance among each other
- Uniform dotted/globular vessels – seen in LSC and secondary lichenification. But here the vessels are typically surrounded by a white halo due to the presence of hypergranulosis
Based on body sites/types – there is not much difference in the dermoscopic features except in the amount of scaling
- Guttate psoriasis – little or absent scaling
- Flexural psoriasis – lack scaling
- Pustular psoriasis – yellow globules and crusts are seen along with dotted vessels and white scales
- Follicular psoriasis – white follicular keratotic plugs which is surrounded by dotted vessels which are arranged uniformly
Also dermoscopy reveals skin atrophy that is not evident clinically – following chronic treatment with potent topical steroids which causes appearance of telangiectatic vessels.