Early recognition & diagnosis
Patient history
Symptoms
Note if lesions are chronic or come and go. Document symptoms such as itching, burning, or pain. Check for joint pain or stiffness that may suggest psoriatic arthritis.
Family history
Ask about PsO or autoimmune conditions in the family.
Triggers and contributing factors
Ask about stress, infections (eg, strep), medications, skin injuries, burns, trauma, obesity, alcohol use, smoking, or cold/chemical exposure.
Physical examination
Examine lesion features, noting onset, duration, and pattern.
Lesions are typically defined as thick plaques with silvery‑white scale on light skin, purple, gray, or brown on dark skin.
Lesions on elbows, knees, and lower back are common.
Lesions may be on the scalp, hairline, and face.
Palms of hands and soles of the feet may be affected, with cracked skin or pustules.
Note nail changes such as pitting, onycholysis (nail lifting), or yellow‑brown discoloration.
Auspitz sign may be present: Removal of scale may cause pinpoint bleeding; patients may report bleeding after scratching.
Other patterns:
- Guttate PsO appears as small red, drop‑like spots often triggered by infection
- Inverse PsO shows smooth red patches in skin folds, including the groin, without scales
- Pustular PsO features white pustules on red skin
- Erythrodermic PsO involves widespread bright red, peeling skin, sometimes covering nearly the entire body
PsO appearance
| Feature | PsO on lighter skin | PsO on darker skin |
|---|---|---|
Color of plaques | Red or pink | Purple, violaceous, or dark brown |
Scaling | Silvery‑white, sharply contrasting | Gray, silvery, brown and sometimes less visible scale |
Contrast with surrounding skin | High contrast; plaques sharply defined | Lower contrast; plaque borders may appear less sharply defined visually, with greater reliance on texture, induration, and scale |
Post‑inflammatory changes | Less common; may have mild, transient pink discoloration after plaques clear | More common; may have persistent dark (hyperpigmented) or light (hypopigmented) patches after plaques clear |
Scalp involvement | Redness and scale are obvious | Scaling more prominent than redness; redness may be missed |
PsO appearance | ||
Images are Janssen‑owned from clinical trials. | ||
Differential diagnosis of PsO
Consider these conditions with similar presentations
Eczema
Favors flexor surfaces; lacks thick silvery scale, plaques are less well‑defined/poorly demarcated than PsO.
Seborrheic dermatitis
Ill‑defined erythematous patches with greasy yellow scale on the scalp/face/chest.
Fungal infections
Annular plaques with scaly, erythematous border; rule out with fungal scraping if tinea suspected.
Pityriasis rosea
Acute, self‑limiting eruption that typically begins with a herald patch (salmon- or pink‑brown‑colored plaque with fine collarette scale) followed by multiple smaller oval plaques that align along skin cleavage lines in a “Christmas tree” distribution on the trunk and proximal extremities.
Cutaneous t‑cell lymphoma
Flat, irregular, red pruritic lesions in areas not exposed to the sun; includes mycosis fungoides, which presents as persistent, variably scaly patches or plaques with predilection for sun‑protected areas.
Discoid lupus erythematosus
Well‑demarcated plaques with adherent scale often on the face ears, or scalp that heal with scarring and dyspigmentation.
Superficial nonmelanoma skin cancer
Persistent, slow‑growing, pink‑red scaly patch or plaque on areas of chronic sun exposure.
Drug eruptions
Rapid onset of numerous small, sterile pustules on red, inflamed skin usually occurring 1–2 days after drug exposure, often accompanied by fever.
An online dermatology resource featuring images of various skin conditions, including PsO, can be accessed at https://dermnetnz.org.
Consider biopsy if diagnosis is in doubt