History and exam

Key diagnostic factors

common

skin lesions

Typically erythematous, circumscribed scaly papules and plaques on elbows, knees, extensor surfaces of limbs, scalp, and, less commonly, nails, ears, and umbilical region.[Figure caption and citation for the preceding image starts]: Nail psoriasis - pitted nailsFrom the collection of Professor Tsu-Yi Chuang, MD, MPH, FAAD; used with permission [Citation ends].com.bmj.content.model.Caption@787230e

In plaque psoriasis, there are raised inflamed plaque lesions with a superficial silvery-white scaly eruption. The scale may be scraped away to reveal inflamed and sometimes friable skin beneath.[2] Pinpoint bleeding points are known as Auspitz's sign.[Figure caption and citation for the preceding image starts]: Plaque psoriasis on legsFrom the collection of Professor Tsu-Yi Chuang, MD, MPH, FAAD; used with permission [Citation ends].com.bmj.content.model.Caption@33b34843[Figure caption and citation for the preceding image starts]: Plaque psoriasis on backFrom the collection of Professor Tsu-Yi Chuang, MD, MPH, FAAD; used with permission [Citation ends].com.bmj.content.model.Caption@9365c8a[Figure caption and citation for the preceding image starts]: Plaque psoriasis on kneeFrom the collection of Professor Tsu-Yi Chuang, MD, MPH, FAAD; used with permission [Citation ends].com.bmj.content.model.Caption@264651ce[Figure caption and citation for the preceding image starts]: Plaque psoriasis on footFrom the collection of Professor Tsu-Yi Chuang, MD, MPH, FAAD; used with permission [Citation ends].com.bmj.content.model.Caption@52474b4a[Figure caption and citation for the preceding image starts]: Plaque psoriasis on scalpFrom the collection of Professor Tsu-Yi Chuang, MD, MPH, FAAD; used with permission [Citation ends].com.bmj.content.model.Caption@73b8ea9a

In guttate psoriasis, there are widespread, erythematous, fine, scaly papules (water drop appearance) on trunk, arms, and legs. The lesions often erupt after an upper respiratory infection.[2][Figure caption and citation for the preceding image starts]: Guttate psoriasisFrom the collection of Professor Tsu-Yi Chuang, MD, MPH, FAAD; used with permission [Citation ends].com.bmj.content.model.Caption@1715dc6e

In pustular psoriasis, acute generalised pustular psoriasis (von Zumbusch) is rare, severe, and urgent; palmoplantar pustulosis affects palms and soles and is chronic.[2][Figure caption and citation for the preceding image starts]: Pustular psoriasisFrom the collection of Professor Tsu-Yi Chuang, MD, MPH, FAAD; used with permission [Citation ends].com.bmj.content.model.Caption@62ab401d

In erythroderma (erythrodermic psoriasis), there is generalised erythema with fine scaling. It is often associated with pain, irritation, and sometimes severe itching.[2][Figure caption and citation for the preceding image starts]: ErythrodermaFrom the collection of Professor Tsu-Yi Chuang, MD, MPH, FAAD; used with permission [Citation ends].com.bmj.content.model.Caption@42c5138b

Other diagnostic factors

common

family history

Most people with psoriasis have a positive family history.[11][16]

Studies of monozygotic twins, linkage studies, and genome-wide association studies provide evidence that psoriasis has a genetic predisposition.[11][12][13]

joint swelling or pain

Psoriatic arthritis occurs in 20% of people with psoriasis and can point towards a diagnosis of cutaneous psoriasis.[3] 

Psoriatic arthritis has several presentations including joint pain, tendinitis, enthesitis, or dactylitis. In most cases arthritis presents after the onset of cutaneous psoriasis, but it may be a presenting sign.[49]

Risk factors for psoriatic arthritis include early age at first presentation, female sex, polyarticular involvement, and genetic predisposition.[50] 

Risk factors

strong

genetic

Most people with psoriasis have a positive family history.[11][16]

Studies of monozygotic twins, linkage studies, and genome-wide association studies provide evidence that psoriasis has a genetic predisposition.[11][12][13]

Psoriasis has been linked to a number of genes, with the strongest association to those involved in the immune response, particularly IL23R, IL12B, and tumour necrosis factor (TNF)-alpha.[14]

infection

Guttate psoriasis is often observed subsequent to upper respiratory infection, such as streptococcal pharyngitis. It may also be associated with HIV infection. Viral infection, immunisation, and any intercurrent illness have been linked to flares of guttate and plaque psoriasis.[16][19]

local trauma

Trauma, such as surgical scars and injection sites, may result in the appearance of new psoriatic lesions at the site of injury.[29] This is known as the Koebner phenomenon.

medications

Several medications may induce or exacerbate pre-existing psoriasis (the incidence of psoriasis exacerbation is generally greater than that of psoriasis induction), including antihypertensives and lithium.[30]

The latency period between drug ingestion and psoriasis flares varies, and can be considerable for certain medications.[31][32]

weak

stress

Stress and sleep deprivation are recognised to exacerbate psoriasis. Stress reduction techniques may be useful in managing exacerbations.[33][34]

smoking

Systematic reviews and meta-analyses have found that that smoking is a risk factor for the development of psoriasis.[35][36]

Risk increases the greater the number of cigarettes smoked per day and in longer durations of smoking.[35]

ethnicity

Psoriasis is reported to be twice as common in white people than in black people.[7][37]

alcohol

Alcohol consumption may be associated with increased risk of psoriasis.[38][39]

Heavy alcohol intake exacerbates psoriasis and complicates treatment by increasing the inflammatory response, altering pharmacology, and potentially reducing adherence to medication.[40][41]

greater body mass index (BMI)

Obesity is more prevalent in people with psoriasis (30% to 40%) compared with the general population.[42] 

Obesity as measured by BMI, waist circumference, waist-to-hip ratio, and weight gain is associated with increased risk of psoriasis and exacerbation of pre-existing psoriasis.[43][44][45][46]

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