Diagnosis: Chronic plaque psoriasis
Psoriasis is a noninfectious inflammatory skin disorder characterized by well-defined erythematous plaques that bear large, adherent silvery scales. It can appear at any age, but 75% of patients have an onset before the age of 40 years.1
Psoriasis was once considered a hyperproliferative disorder, but is now recognized as an autoimmune phenomenon involving activation of T-cells. As a result, new immunosuppressive agents have been added to the list of traditional therapies, opening a new chapter of immunomodulatory therapy.
Clinical presentations of psoriasis
In its classic presentation, psoriasis does not pose a diagnosis challenge to most clinicians—it presents as a sharply demarcated erythematous plaques with silvery white scales. Although many classification systems exist, a concise classification is included in TABLE 1. Skin conditions to be considered for differential diagnosis are summarized in TABLE 2. The US Food and Drug Administration defines “severe” psoriasis as involving more than 20% of body surface area.2
TABLE 1
Classification of psoriasis
| Chronic plaque psoriasis | Symmetrical plaques up to 20 cm in diameter, with a predilection for the elbows, knees, presacrum, scalp, hands, and feet |
| 5%–30% of patients develop a seronegative arthropathy | |
| Guttate psoriasis | Numerous small papules and plaques over the upper trunk and proximal extremities |
| Most common form of psoriasis in children, and may be triggered by any streptococcal infection including streptococcal perianal dermatitis | |
| Spontaneous remission is the rule | |
| Generalized pustular and erythrodermic psoriasis | Uncommon variants associated with high morbidity that may be fatal |
TABLE 2
Differential diagnosis
| Fungal infections |
| Squamous cell carcinoma in situ |
| Cutaneous T-cell lymphoma |
| Discoid eczema |
| Seborrhoeic eczema |
| Pityriasis rosea |
| Secondary syphilis |
| Hypertrophic lichen planus |
| Nummular dermatitis |