6-11: Psoriasis

General Considerations

Psoriasis is a common benign, chronic inflammatory skin disease with both a genetic basis and known environmental triggers. Injury or irritation of normal skin tends to induce lesions of psoriasis at the site (Koebner phenomenon) (eFigure 6–15). Obesity worsens psoriasis, and significant weight loss in obese persons may lead to substantial improvement. Psoriasis has several variants—the most common is the plaque type (eFigure 6–13) (eFigure 6–16). Eruptive (guttate) psoriasis consisting of myriad lesions 3–10 mm in diameter occurs occasionally after streptococcal pharyngitis. Rarely, life-threatening forms (generalized pustular and erythrodermic psoriasis) may occur.

Clinical Findings

There are often no symptoms, but itching may occur and be severe. Favored sites include the scalp, elbows, knees, palms and soles, and nails. The lesions are red, sharply defined plaques covered with silvery scale (Figure 6–7). The glans penis and vulva may be affected. Occasionally, only the flexures (axillae, inguinal areas) are involved (termed inverse psoriasis). Fine stippling (“pitting”) in the nails is highly suggestive of psoriasis (Figure 6–8) (eFigure 6–17) as is onycholysis. The combination of red plaques with silvery scales on elbows and knees, with scaliness in the scalp or nail findings, is diagnostic. Patients with psoriasis often have a pink or red intergluteal fold. Not all patients have findings in all locations, but the occurrence of a few may help make the diagnosis when other lesions are not typical. Some patients have mainly hand or foot dermatitis and only minimal findings elsewhere. There may be associated arthritis that is most commonly distal and oligoarticular, although the rheumatoid variety with a negative rheumatoid factor may occur. The psychosocial impact of psoriasis is a major factor in determining the treatment of the patient.