# Pityriasis Rubra Pilaris

> Pityriasis rubra pilaris for NEET-PG Dermatology: Griffiths types 1-6, islands of sparing, orange keratoderma, checkerboard histology, treatment.

- Canonical URL: https://prepelephant.com/topics/neet-pg/dermatology/pityriasis-rubra-pilaris
- Exam / course: NEET-PG · Subject: Dermatology
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-02
- Last updated: 2026-10-02
- How to cite: "Pityriasis Rubra Pilaris", PrepElephant, https://prepelephant.com/topics/neet-pg/dermatology/pityriasis-rubra-pilaris

## Direct answer

Six Griffiths types, one histology: pityriasis rubra pilaris (PRP) is a papulosquamous disorder of follicular plugging that spreads cephalocaudally into salmon-orange erythroderma with palmoplantar keratoderma, unmistakably punctuated by islands of sparing — normal skin islands within the red sea. Classical adult type 1 begins in the scalp and descends over weeks, may cause ectropion, and clears in one to three years in the majority; type 6 rides alongside HIV with acne conglobata and lichen spinulosus and responds poorly. Histology shows the quotable checkerboard sign — alternating horizontal and vertical orthokeratosis and parakeratosis — with thick suprapapillary plates and a sparse infiltrate. Acitretin is first-line therapy, with methotrexate and off-label biologics behind it.

## What you must remember

- **Type map (Griffiths):** 1 classical adult (over half of cases, scalp-first descent, best prognosis); 2 atypical adult (alopecia, long course); 3 classical juvenile (onset in the first decade, behaves like type 1); 4 circumscribed juvenile (prepubertal, elbows and knees); 5 atypical juvenile, often familial; 6 HIV-associated (acne conglobata, lichen spinulosus, nodulocystic lesions, refractory).
- **Three clinical signatures:** salmon-orange generalised erythema with follicular plugging, waxy orange palmoplantar keratoderma, and islands of sparing — the triad the photographic question is built on.
- **Cephalocaudal spread:** scalp and face first, trunk then extremities, ending in exfoliative erythroderma with ectropion and alopecia in severe type 1.
- **Histology quote:** alternating orthokeratosis and parakeratosis in horizontal and vertical planes ("checkerboard"), thickened suprapapillary plates, sparse dermal infiltrate — a favourite slide description.
- **Therapy ladder:** acitretin 0.5-1 mg/kg (practical start 25-50 mg daily) is first line; methotrexate next; TNF, IL-12/23 and IL-17 inhibitors reported in series — the IL-17 logic mirrors psoriasis.
- **Type 1 natural history:** most patients clear within 1-3 years and stay clear — the prognostic sentence exams reward; types 2, 4 and 5 run chronic courses.
- **Supportive care:** emollients by the kilogram, keratolytics for keratoderma, ocular lubrication for ectropion, and monitor erythroderma complications — thermoregulatory loss, high-output cardiac strain, sepsis risk.
- **Indian practice note:** the psoriasis mimic is strong; biopsy before labelling, because PRP lacks the Auspitz sign and responds poorly to phototherapy.

## Telling it apart from erythrodermic psoriasis: a reasoned comparison

Both diseases can put a red, scaly patient in the bed; the discrimination is clinical first and histological second. Walk the bedside: PRP shows follicular, nutmeg-grater papules, orange-hued palmoplantar waxy keratoderma, and — decisively — sharp islands of sparing scattered across trunk and limbs. Erythrodermic psoriasis tends to carry larger flaky sheets, nail pitting or oil drops, a personal history of plaques and arthritis, and Auspitz positivity on scraping. When the clinical picture sits on the fence, the biopsy arbitrates: PRP's checkerboard parakeratosis with thick suprapapillary plates contrasts with psoriasis's regular acanthosis, parakeratosis and clubbed rete ridges with neutrophils in the stratum corneum. The stakes are practical — phototherapy, a psoriasis staple, can flare PRP, and biologics chosen on the wrong label behave unpredictably — so the biopsy before immunosuppression is not academic caution but the hinge of management.

## How the exam frames it

Expect a photograph with normal-skin islands inside orange erythroderma, or a histology slide with alternating ortho- and parakeratosis; either way the answer spells PRP. The one-liner comparisons are predictable: versus psoriasis (islands of sparing, negative Auspitz, checkerboard histology), versus ichthyosis (acquired pattern without follicular plugging), and the HIV vignette — young man with generalized erythroderma plus acne conglobata and lichen spinulosus, where type 6 is the expected answer and antiretroviral therapy is part of it. Dose questions like acitretin's weight-based range appear in viva form; the defensible answer quotes 0.5-1 mg/kg with monitoring of lipids and liver enzymes, and a firm statement that no therapy is curative — most type 1 disease clears itself on a clock of one to three years.

## Frequently asked questions

### Which feature most reliably distinguishes PRP from erythrodermic psoriasis?
Sharp islands of uninvolved skin within confluent salmon-orange erythroderma, supported by the checkerboard histology of alternating ortho- and parakeratosis.

### What characterises Griffiths type 6 PRP?
HIV-associated disease with acne conglobata, lichen spinulosus and nodulocystic lesions, resistant to conventional therapy.

### What is the first-line systemic treatment?
Acitretin at 0.5-1 mg/kg per day, with methotrexate and off-label biologics as alternatives in refractory disease.

### How does classical adult PRP typically evolve?
Cephalocaudal spread from the scalp to erythroderma over weeks, then spontaneous clearance within one to three years in the majority.

### Why is phototherapy used cautiously in PRP?
PRP can flare with phototherapy, unlike psoriasis, so retinoids are preferred before light-based treatment is attempted.