2.3.1.3 Clinical manifestations
Psoriasis could be categorized into psoriasis vulgaris，psoriasis arthropathica（psoriatic arthritis），erythrodermic psoriasis，and pustular psoriasis according to their respective clinical patterns.Psoriasis vulgaris accounts for more than 90％of cases，and the other two types listed above（except psoriatic arthritis）are frequently the exacerbation of psoriasis vulgaris caused by triggers such as strongly irritating topical treatments，the sudden withdrawal of systemic glucocorticoids or immunosuppressants，infection，or even mental stress.
1.Psoriasis vulgaris
This type of psoriasis begins with red papules or maculopapules that gradually becomes well-demarcated red plaques in a variety of morphologic patterns（e.g.，guttate，nummular，geographic，ostraceous），covered with thick silvery scales.Scraping off these lamellar scales is similar to scraping off wax drippings（candle wax phenomenon），which then exposes a shiny reddish translucent film on the surface of the lesion（film phenomenon）.When the film is removed completely，punctuate spots of bleeding appear within a few seconds（Auspitz's sign）.The candle wax phenomenon，the film phenomenon，and the punctate bleeding are all important diagnostic clues for psoriasis.The degree of pruritus vary from patients to patients.
2.Psoriasis arthropathica
It is also known as psoriatic arthritis.5％-8％of psoriatic patients eventually develop psoriatic arthritis.Psoriatic arthritis typically has a chronic course.Psoriasis lesions usually precede the onset of joint symptoms.Psoriatic arthritis can affect any particular joint，but is more common affecting large joints of the lower extremities，the distal joints of the fingers and toes，and even the back and sacroiliac joints.Marked nail damage often accompanies digital joint arthritis.The involved large joints may resemble rheumatoid arthritis with joint malformation.However，unlike rheumatoid arthritis，the rheumatoid factor in psoriatic arthritis is usually negative.Patients with spine and sacroiliac joint involvement show a strong correlation with HLA-B27 antigen.(https://www.daowen.com)
3.Erythrodermic psoriasis
This type of psoriasis appears as inflammation and exfoliation of the skin over most of the body surface，in which the small normal-appearing areas look like islands.There is generalized redness and swelling of the skin covered with bran-like scales which may be accompanied with fever and lymphadenopathy.The course of this condition is more persistent and also is more likely to recur.
4.Pustular psoriasis
There are two forms of pustular psoriasis，i.e.，generalized pustular psoriasis and localized pustular psoriasis.①Generalized pustular psoriasis：Here the pustules have a sudden onset and can spread quickly over the entire body.The yellow or yellow-white，pinhead to milium-sized，superficial，sterile，and small pustules occur in groups around old lesions of psoriasis vulgaris or in normal skin，and may coalesce，thereby forming“large lakes”of pus.The skin around the pustules is often red，inflamed and can be painful.Attacks are often preceded by chills，high fever，and other constitutional signs.The patients may present fissured tongue，and thickened and turbid fingernails or toenails when the tongue and nails are involved.Usually the pustules dry up to form crusts within 1-2 weeks，but recurrent attacks can take place.The conditions can be progressive in some patients，presenting with severe symptoms and death from secondary infection and multiple organ failure.②Localized pustular psoriasis：The sterile pustules are distributed symmetrically at the palms and soles only，especially in the thenar or hypothenar eminences or in the central portion of the palms and soles.For each episode，crops of small pustules develop on the erythematous areas and may rupture and crust or desquamate within 1-2 weeks，but new pustules will keep appearing under the scales.The process runs a chronic course with only a slight chance of significant remission.Nails are often involved in these patients，with punctate depressions，transverse grooves，longitudinal ridges，onycholysis，and subungual pus.