Characteristics of psoriasis and contact dermatitis for differential diagnosis
| Characteristics | Psoriasis | Contact dermatitis |
|---|---|---|
| Sites involved | Knees, elbows, scalps, palm and sole, all body | Sites in contact with irritants or allergens |
| Symptoms | Generally none | Burning in irritant form, itching in allergic form |
| Signs | Solitary or multiple erythematous plaques with characteristic adherent silvery white scales, Koebner phenomenon | Erythema, edema, papule and vesicles, fissures in irritant form; hyperkeratosis in chronic form |
| Histology | ||
| Parakeratosis | Moderate or strong, confluent; para-/ortho-keratosis | Mild and in multiple foci |
| Acanthosis | Regular | More irregular |
| Granular layer | Thinner | Normal |
| Capillaries in the upper dermis | Tortuous or dilatate | Horizontal |
| Lymphocytic exocytosis in epidermis | No (less likely) | Yes |
| Edema of papillary dermis | No (less likely) | Yes |
| Spongiosis | More frequent | Less frequent |
| Munro microabscesses | Yes | No |
| Prevention | Not available | Avoidance of contact with irritants or sensitizing agents |