Key Points

• Affects up to 2% of the population.
• Chronic disorder in those with a polygenic predisposition combined with triggering factors such as infections (especially streptococcal pharyngitis, but also HIV infection) or medications (e.g. interferon, β-blockers, lithium, or oral CS taper).
• Koebner phenomenon – elicitation of psoriatic lesions by traumatizing the skin.
• Common sites.
– Scalp.
– Elbows and knees.
– Nails, hands, feet, trunk (intergluteal fold).
• Skin lesions.
– Most commonly – well-demarcated, erythematous plaques with silvery scale (Fig. 6.1).
– Other lesions include sterile pustules, glistening plaques in intertriginous zones.
• Histopathologic findings.
– 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.
• Pathogenesis.
– Regarded as a T-cell-driven disease involving cytokines, including TNF-α and IL-23 (stimulates Th17 cells).
– 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).
• May be generalized (Fig. 6.5).
• Lesions may be surrounded by a peripheral, blanching ring (Woronoff ’s ring), especially when patient is receiving phototherapy.

Guttate Psoriasis

• Typical lesion – small papule or plaque (3 mm to 1.5 cm) with adherent scale (Fig. 6.6).
• Generalized distribution.
• Affects children > adults.
• 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

• Linear, erythematous, scaly lesions that often follow the lines of Blaschko.
• DDx: inflammatory linear verrucous epidermal nevus (ILVEN; follows the lines of Blaschko; resistant to therapy), epidermal nevus with superimposed psoriasis.

Erythrodermic Psoriasis

• Generalized erythema of the skin, with areas of scaling.
• Gradual or acute onset.
• 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).
– Often associated fever.
– Triggering factors – pregnancy (termed impetigo herpetiformis), rapid tapering of CS, hypocalcemia, infections.
– DDx: acute generalized exanthematous pustulosis (AGEP; pustular drug reaction) (see Chapter 17).
• Palmoplantar (pustulosis).
– Sterile pustules on palms/soles (Fig. 6.8).
– May have no evidence of psoriasis elsewhere.
– Triggering factors – infections, stress.
– May be aggravated by smoking.
– Associated with inflammatory bone lesions (see Chapter 21).
• Annular pattern (Fig. 6.9).
– DDx: includes Sneddon–Wilkinson disease (see below).
• Exanthematic type.
– Significant overlap with AGEP.
• Localized pattern – within plaques, often due to irritants (Fig. 6.10).
• Acrodermatitis continua (of Hallopeau).
– Erythema and scale of distal digit with pustules (Fig. 6.11).
– Often associated fever.

 

Special Sites

Scalp

• Well-demarcated, erythematous plaques with silvery scale.
• Scale may be attached for some distance onto scalp hairs, giving an asbestos-like appearance (pityriasis amiantacea).
• Occasionally alopecia may be seen within lesions.
• DDx: seborrheic dermatitis (more diffuse pattern), tinea capitis, dermatomyositis.

Flexural (Inverse Psoriasis)

• Shiny, pink, well-demarcated thin plaques with minimal scale (Fig. 6.12).
• Common sites include the axilla, inguinal crease, intergluteal cleft, inframammary area, and retroauricular fold.
• Sebopsoriasis – seborrheic dermatitis and psoriasis are at either ends of a spectrum, with intermediate forms termed sebopsoriasis.
• Additional DDx: seborrheic dermatitis, candidiasis, tinea cruris, erythrasma, granular parakeratosis (see Fig. 13.4).

Oral

• Migratory, annular lesions with central denuded areas and white borders.
• Similar to geographic tongue clinically and histopathologically.

Nail (See Chapter 58)

• Fingernails > toenails (Fig. 6.13).
• Associated with psoriatic arthritis.
• Findings include nail pitting, oil spots (salmon patch), onycholysis with proximal red rim, splinter hemorrhages, subungual debris.

Sneddon–Wilkinson Disease (Subcorneal Pustular Dermatosis)

• Often begins in body folds or major intertriginous zones.
• Lesions are annular with superficial pustules on the border.
• Classic sign is a half and half pustule with clear fluid superiorly and pus inferiorly (dependent portion).
• Two schools of thought – this disease is (1) a variant of psoriasis vs. (2) a separate entity (Fig. 6.14).

Psoriatic Arthritis (See Table 6.1)

• Seen in 5–30% of patients with cutaneous psoriasis.
• Most commonly is an asymmetric oligoarthritis affecting the distal interphalangeal joints (Fig. 6.15).
• More rarely, but classically, is arthritis of all the interphalangeal joints.
• Occasionally, presentation is rheumatoid arthritis-like, affecting small- and medium-sized joints symmetrically.
• Arthritis mutilans – rare form with acute, rapidly progressive joint inflammation and destruction; softening and telescoping of the digits.
• Spondylitis and sacroiliitis – axial arthritis as well as arthritis of the knees and sacroiliac joints; may be HLA-B27-positive and may have associated inflammatory bowel disease or uveitis.
• DDx: reactive arthritis (previously referred to as Reiter’s disease).
– Urethritis, arthritis, ocular findings (e.g., conjunctivitis), and oral ulcers in addition to psoriasiform lesions, especially on the soles (keratoderma blennorrhagicum) or genitalia (balanitis circinata) (Fig. 6.16).
– More common in men.
– Strongly associated with HLA-B27.
– Course is often self-limited.
– May be severe in HIV-positive individuals.

Treatment

• Topical agents.
– First-line.
• CS (Table 6.2).
• Vitamin D3 analogues (calcipotriene, calcitriol) (Table 6.3).
– Second-line.
• Calcineurin inhibitors (may be first-line for sensitive areas such as the face or flexures).
• Tars (e.g. liquor carbonis detergens [LCD] 5%).
• Anthralin.
• Tazarotene.
• Phototherapy and systemic agents.
– First-line.
• Phototherapy – UVB (narrowband or broadband > PUVA) (Table 6.4); if thick keratotic plaques, can combine with oral retinoids.
• Methotrexate (oral or intramuscular, occasionally subcutaneous) (Table 6.5).
• Oral retinoids (e.g. acitretin, isotretinoin).
– Second-line systemic.
• Targeted immunomodulators (‘biologic’ agents) (Tables 6.6 and 6.7).
• Cyclosporine.
• See Table 6.8 for treatment options in patients with comorbidities or special situations.
• See Table 6.9 for the recommended laboratory evaluation for patients receiving targeted immunomodulators.