Background

• Occurs in 1%-3% of the population. Transmitted genetically, with variable penetrance and disease manifestations due to environmental triggers
• Precipitants:
  • Medications  (beta-blockers, antimalarials, lithium)
  • Systemic steroids, while effective at clearing psoriasis, can cause severe flares when withdrawn
  • Koebner’s phenomenon: Trauma may trigger lesions at sites of injury
  • URI’s (especially streptococcal) or cutaneous infections
  • Stress, alcohol
  • Systemic steroid withdrawal
• Associated with diabetes, metabolic syndrome, arthritis, inflammatory bowel disease, malignancy (lymphoma and skin cancer), depression
• Independent risk factor for cardiovascular morbidities, possibly in relation to inflammation 
• Can be more emotionally than physically disabling, affecting patients’ self-image and leading to activity avoidance, some of which (e.g., sunbathing) could have a therapeutic benefit

Evaluation

• Distribution:
  • Scalp, behind the ears, palms, and soles
  • Extensor extremities (knees and elbows)
  • Periumbilical and sacral areas
  • Gluteal cleft “gluteal pinking” = pathognomic for psoriasis
  • Nail changes (see below)
  • Usually spares palms, soles, and face
• Morphology:
  • Well-demarcated pink papule or plaque with overlying adherent silvery scale
  • May have associated pustules
  • Can be confused with eczema or seborrheic dermatitis
  • Guttate psoriasis can resemble secondary syphilis or pityriasis rosea
• Nail changes:
  • Pitting: Nail plate cells are shed much like the psoriatic skin scale, leaving punched out depressions. Not specific (can occur with eczema, fungal infections, alopecia)
  • Onycholysis: Separation of the nail from the nail bed, often simulating a fungal infection
  • Oil spots: Yellow-brown spots under the nail plate
• Psoriatic arthritis:
  • 5-42% of psoriasis associated with seronegative spondyloarthropathy
  • The most common form is asymmetric oligoarthritis of small joints (hands, feet, wrists), but can also involve spine and entheses
  • Unlike rheumatoid arthritis, frequently involves the DIPs

Psoriasis variants and characteristics

• Plaque psoriasis: Most common variant, erythematous plaques with well-defined margins and thick silvery scale in a classic distribution described above
• Guttate psoriasis: Acute eruption of multiple small (<1cm) psoriatic lesions; primarily involves trunk in children/young adults; associated with a recent Strep infection. Tx: UV
• Pustular psoriasis: May be life-threatening with widespread erythema/scaling and superficial pustules arising from suddenly formed erythematous areas in the flexural regions. Risk of hypocalcemia, high output heart failure, electrolyte abnormalities.  Tx: infliximab, cyclosporine, acitretin, derm consult
• Inverse psoriasis: Involves intertriginous areas rather than extensor surfaces. Scale is typically absent. Can be confused for candida infection or tinea.
• Erythrodermic psoriasis: Rare, generalized erythema/scaling at high risk for complications due to loss of skin barrier protection; warrants hospital admission for intensive topical steroid therapy and monitoring of fluid loss and high output cardiac failure.

Treatment

• Treat until the skin feels normal (close eyes and run finger along plaque)
• Topicals have variable efficacy and treatment dissatisfaction and nonadherence is high.
• Psoriasis is not a scarring condition

Table 4: Treatment of Psoriasis

References

Nestle FO, Kaplan DH, Barker J. Psoriasis. N Engl J Med. 2009;361(5):496-509.

Schon MP, Boehncke WH. Psoriasis. N Engl J Med. 2005;352(18):1899-912.          

Weigle N, McBane S. Psoriasis. Am Fam Physician. 2013 May 1;87(9):626-33.

Habif TP. Clinical Dermatology: A Color Guide to Diagnosis and Therapy - Chronic Pruritus. 6^th Edition, Saunders. 2015: p215-217.