6
Psoriasis
Key Points
• Affects up to 2% of the population.
• Koebner phenomenon – elicitation of psoriatic lesions by traumatizing the skin.
– Scalp.
– Nails, hands, feet, trunk (intergluteal fold).
– Most commonly – well-demarcated, erythematous plaques with silvery scale (Fig. 6.1).
Fig. 6.1 Psoriatic plaques. Note the sharp demarcation and silvery scale. Courtesy Julie V. Schaffer, MD.
– Other lesions include sterile pustules, glistening plaques in intertriginous zones.
– Regular acanthosis, confluent parakeratosis with neutrophils, hypogranulosis, dilated blood vessels (see Chapter 1).
• Major systemic association is psoriatic arthritis (see Table 6.1), most commonly presenting as asymmetric oligoarthritis of hands/feet; the metabolic syndrome is also common.
– Genes that have been associated with psoriasis include those encoding caspase recruitment domain family member 14 (CARD14, a regulator of NF-κB signaling) and, for generalized pustular psoriasis, the IL-36 receptor antagonist (a regulator of IL-8 production and IL-1β responses).
Variants
Chronic Plaque Psoriasis
• Typical lesion – well-demarcated, erythematous plaque with silvery scale.
• Often symmetrical lesions on the elbows and knees; additional sites include the scalp, presacrum, hands, feet, intergluteal fold, and umbilicus (Figs. 6.2–6.4).
Fig. 6.3 Palmoplantar psoriasis. Erythematous scaling plaques of the palmar (A) and plantar surfaces (B). Occasionally, there is well-demarcated hyperkeratosis with minimal erythema (C). A, Courtesy, Peter C. M. van de Kerkhof, MD.
Fig. 6.4 Psoriasis of the genitalia. Erythematous plaques with scale on the penis and scrotum. Courtesy, Peter C. M. van de Kerkhof, MD.
Guttate Psoriasis
• Typical lesion – small papule or plaque (3 mm to 1.5 cm) with adherent scale (Fig. 6.6).
Fig. 6.6 Guttate psoriasis. A Small discrete papules and plaques of guttate psoriasis in an adolescent; note the Koebner phenomenon. B Numerous papules due to the Koebner phenomenon after a sunburn. B, Courtesy Ronald P. Rapini, MD.
• Often preceded by an upper respiratory tract infection.
• In children, may have spontaneous remission but often responds well to UVB phototherapy.
• DDx: pityriasis rosea, syphilis, id reaction to tinea pedis, and small plaque parapsoriasis.
Linear Psoriasis
Erythrodermic Psoriasis
• Generalized erythema of the skin, with areas of scaling.
• Nail changes, facial sparing, and a history of typical plaque-type psoriasis may be helpful clues.
• May be seen after abrupt tapering of medications, especially CS.
• DDx: other causes of erythroderma, e.g., pityriasis rubra pilaris, generalized atopic dermatitis, Sézary syndrome (see Table 8.2).
Pustular Psoriasis
• Generalized pustular psoriasis (von Zumbusch pattern).
– Erythema and sterile pustules arising within erythematous, painful skin; lakes of pus characteristic (Fig. 6.7).
Fig. 6.7 Pustular psoriasis. Large areas of erythema with numerous pustules. Confluence of pustules creates lakes of pus. Courtesy, Julie V. Schaffer, MD.
– DDx: acute generalized exanthematous pustulosis (AGEP; pustular drug reaction) (see Chapter 17).
– Sterile pustules on palms/soles (Fig. 6.8).
Fig. 6.8 Pustulosis of the palms and soles. Multiple sterile pustules are admixed with yellow-brown macules on the palm.
– May have no evidence of psoriasis elsewhere.
– Triggering factors – infections, stress.
