Psoriasis

Overview
  • Psoriasis is a complex auto-inflammatory disease that affects nearly 2% of the US population and is often a life-long, chronic condition. Although the disease is most commonly associated with the skin, the immune derangement is systemic and can affect the joints as well
Pathogenesis
  • The immune pathogenesis of psoriasis is under active investigation and is likely initiated by derangements of T-cells, especially Th1 Cells. Given the therapeutic effectiveness of TNF-alpha inhibitors, derangements of inflammatory cytokines are clearly involved. Whatever initiating events, inflammation of the skin results in an enormous acceleration of cell division within the epidermis, thus yielding the thickened scaling plaque of psoriasis.
Morphology
  • Gross Morphology
    • Psoriasis classically presents as well-demarcated, erythematous plaques with a silvery scale and typically involves the extensor surfaces, scalp, and sacrum. When the scale is scraped off, tiny puncta of hemorrhage can be observed, termed the "Auspitz Sign". Lesions are typically bilateral and symmetric. Nails are often involved and can display small pits and separation of the nail fromthe nail bed, termed onycholysis. It should be pointed out that these descriptions are typical of the most common "Plaque" subtype of psoriasis and other subtypes, such as guttate, pustular, erythrodermic, inverse exist and will not be discussed further.
  • Histology
    • The morphology of psoriasis is characterized by acanthosis with downward extension of the epidermal rete ridges. The consequently elongated dermal papillae possess small tortuous vessels which can bleed when the overlying epidermis is scraped off and are thus responsible for the "Auspitz Sign" described below. Hyperkeratosis and parakeratosis are observed and collections of neutrophils, termed "Munroe Abscesses", can be seen in the stratum corneum.
Clinical Consequences
  • Psoriasis typically develops gradually, often in the third decade, and follows a waxing-waning course with occasional flares in the context of chronic therapy. Explosive onset of psoriasis should make the clinician suspicious for HIV infection. Psoriatic plaques are typically not pruritic and most patients are bothered by their cosmesis.
  • In a subset of individuals, patients can develop arthritis. Psoriatic arthritis (see page) is a joint-destructive process and typically involves the joints of the fingers
Treatment
  • A wide variety of therapies can be used for psoriasis and a detailed understanding is likely unnecessary for early medical students. Briefly, mild cases are often treated with topical corticosteroids, topical Vitamin D derivatives, and topical retinoids. Ultraviolet therapy of lesions in combination with psoralen, a DNA-binding chemical, has also been used successfully. More severe cases are often treated systemically with methotrexate, systemic retonoids, systemic cyclosporine, or biologics that target TNF-alpha