Dermatology, Venereology and Leprosy
Papulosquamous Disorders and Psoriasis
Psoriasis for MBBS and NEET-PG: plaque, guttate and pustular forms, Auspitz sign, Koebner, nail and joint disease, topical and systemic therapy, mapped to NMC codes DR3.
MedNext Academy | 3 min read
Papulosquamous Disorders and Psoriasis
Psoriasis for MBBS and NEET-PG: plaque, guttate and pustular forms, Auspitz sign, Koebner, nail and joint disease, topical and systemic therapy, mapped to NMC codes DR3.
Psoriasis is the flagship papulosquamous disease and a heavily tested topic. This chapter covers its immune-driven pathogenesis, the recognition of silvery-scaled plaques, the Auspitz sign and Koebner phenomenon, nail and joint involvement, and a treatment ladder from topical vitamin D analogues to biologics, alongside the key papulosquamous differentials.
High-yield: Papulosquamous Disorders and Psoriasis
- Psoriasis is a chronic immune-mediated disease with T-cell-driven epidermal hyperproliferation, giving well-defined red plaques with silvery scale.
- Chronic plaque psoriasis favours the extensor surfaces of the elbows and knees, the scalp and the sacrum.
- The grattage test or Auspitz sign shows pinpoint bleeding when the scale is scraped off, reflecting dilated dermal capillaries in thinned suprapapillary plates.
- The Koebner phenomenon produces psoriatic lesions at sites of trauma such as scratch marks and surgical scars.
- Nail changes include pitting, onycholysis, subungual hyperkeratosis and the oil-drop sign.
- Guttate psoriasis is a shower of small drop-like plaques in a young person, classically two to three weeks after a streptococcal sore throat.
- Psoriatic arthritis affects a minority of patients, may be seronegative and can cause the pencil-in-cup deformity on radiographs.
- Erythrodermic and generalised pustular psoriasis are severe forms that can be life-threatening and may be precipitated by abrupt steroid withdrawal.
- Histology shows parakeratosis, acanthosis with elongated rete ridges, and neutrophil collections called Munro microabscesses.
- Topical treatments include vitamin D analogues such as calcipotriol, topical corticosteroids, coal tar and dithranol.
- Phototherapy with narrowband ultraviolet B is used for extensive disease not controlled by topical agents.
- Systemic options for severe or arthritic disease include methotrexate, ciclosporin, acitretin and biologic agents.
- Systemic corticosteroids are avoided in psoriasis because withdrawal can trigger a pustular or erythrodermic flare.
- Lichen planus, pityriasis rosea and secondary syphilis are the main papulosquamous differentials of psoriasis.
Psoriasis clinical clues
- **Plaque:** Well-defined red plaque with silvery scale on extensor surfaces and scalp.
- **Auspitz sign:** Pinpoint bleeding on scraping scale (grattage test).
- **Nails:** Pitting, onycholysis, subungual hyperkeratosis, oil-drop sign.
- **Severe forms:** Erythrodermic and pustular psoriasis; avoid systemic steroids.
NMC competencies in this chapter
- **DR3.1:** Distinguishing psoriatic lesions from other papulosquamous causes
- **DR3.2:** The grattage test and Auspitz sign
- **DR3.3:** Indications and modalities of treatment including topical, systemic and phototherapy
Frequently Asked Questions
What is the Auspitz sign?
Removing the silvery scale of a psoriatic plaque by gentle scraping, the grattage test, reveals pinpoint bleeding points. These come from the dilated capillaries of the thinned suprapapillary epidermis.
Why are systemic steroids avoided in psoriasis?
Stopping systemic corticosteroids can precipitate a severe rebound in the form of generalised pustular or erythrodermic psoriasis, so they are not used to control ordinary plaque disease.
What triggers guttate psoriasis?
It classically appears in a child or young adult two to three weeks after a streptococcal throat infection, as a sudden shower of small drop-shaped plaques over the trunk.
What nail changes suggest psoriasis?
Pitting, onycholysis, subungual hyperkeratosis and the oil-drop sign are characteristic, and nail involvement is more common in those with psoriatic arthritis.
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