ESSENTIALS OF DIAGNOSIS
Silvery scales on bright red, well-demarcated plaques, usually on the knees, elbows, and scalp.
Nails: pitting and onycholysis (separation of the nail plate from the bed).
Mild itching is common.
May be associated with psoriatic arthritis.
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 6–69). Obesity worsens psoriasis, and significant weight loss may lead to substantial improvement. Psoriasis has several variants—the most common is the plaque type (eFigure 6–70)(eFigure 6–71)(eFigure 6–72) and hand involvement is also common (eFigure 6–73). Eruptive (guttate) psoriasis consisting of numerous, smaller lesions 3–10 mm in diameter occurs occasionally after streptococcal pharyngitis. Rarely, life-threatening forms (generalized pustular and erythrodermic psoriasis) may occur.
Koebner phenomenon on skin of the hands.
Scale—scalp psoriasis. (Reproduced with permission from Richard P. Usatine, MD, in Usatine RP, Smith MA, Mayeaux EJ Jr, Chumley HS. The Color Atlas and Synopsis of Family Medicine, 3rd ed. McGraw-Hill, 2019.)
Plaque—psoriatic plaque. (Reproduced with permission from Richard P. Usatine, MD, in Usatine RP, Smith MA, Mayeaux EJ Jr, Chumley HS. The Color Atlas and Synopsis of Family Medicine, 3rd ed. McGraw-Hill, 2019.)
Plaque psoriasis involving arm of patient with darker skin. (Used, with permission, from Lindy Fox, MD.)
Psoriasis involving palms of patient with darker skin (Used, with permission, from Kanade Shinkai, MD.)
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 6–22). 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 6–23) (eFigure 6–74) 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. Some patients have mainly hand or foot dermatitis ...