Diagnosing psoriasis in darker skin types

Dr. Andrew F. Alexis of New York City explains how to diagnose psoriasis in Fitzpatrick skin types V and VI

As part of his talk on psoriasis in skin of colour at Skin Spectrum Summit 2019, Dr. Andrew F. Alexis detailed a number of ways that the condition can present differently in darker skin. His comments were part of a larger talk debunking myths surrounding the prevalence of psoriasis in darker skin and comparing the disease’s colour presentation and shape across skin shades. 

He began his talk by discussing how psoriasis in darker skin has come to be understood better over the years. Although it was once considered a “rare” skin condition in people of colour, Dr. Alexis debunked that myth. 

“This was due to underreporting,” he said. “Thankfully, more recent studies have shown that the prevalence of psoriasis in darker skin is far from rare; in fact, these studies have shown the prevalence rate [to be] in the one to two per cent range.”

Dr. Alexis said that sometimes the presentation is classic; it is usually sharply demarcated, brick red or pink, and can have plaques with silvery scales. 

“However, once we get into the more darkly pigmented ranges of the spectrum, including Fitzpatrick type V and type VI, the redness may be masked by melanin and may start to look a little more purple or violaceous than red,” he said.

The sharp lines of demarcation and the characteristic scale will still be present, he said, but because of the purplish hue, it can be difficult to distinguish from linchen planus, another papulosquamous disorder.

One factor that can help differentiate the two disorders is the location on the body where it is found.

“Lichen planus tends to favour the flexural side of extremities, including the wrist and forearm, while psoriasis will be more extensor,” he said. 

The shapes of the lesions of the two disorders differ as well, he said. “In lichen planus, plaques tend to be more flat-topped and polygonal.”

Hyperpigmented lesions ranging from dark brown to red-brown may appear on darker skin as opposed to red lesions on lighter skin.

Certain skincare practices may also hide the character of the scale. In his presentation, Dr. Alexis gave the example of a patient who had a nightly routine of applying petrolatum ointment on his scaly plaques and scraping off the scales with a kitchen knife. 

The takeaway: “This is a lesson to be learned as far as asking about what patients are doing and considering how that might impact the clinical appearance of the plaques in front of us,” said Dr. Alexis.

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A presentation by Dr. Monica Li on underreported, underdiagnosed rosacea in patients with skin of colour. Subscribe to Skin Spectrum Weekly and have each issue sent directly to your phone or inbox.

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