# Psoriatic and Reactive Arthritis

> Psoriatic and reactive arthritis for NEET-PG Orthopaedics covers spondyloarthropathy patterns, pencil-in-cup deformity, sausage digit and enthesitis.

- Canonical URL: https://prepelephant.com/topics/neet-pg/orthopaedics/psoriatic-and-reactive-arthritis
- Exam / course: NEET-PG · Subject: Orthopaedics
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-14
- Last updated: 2026-10-14
- Reference basis: Harrison's Principles of Internal Medicine; Apley's System of Orthopaedics and Trauma
- How to cite: "Psoriatic and Reactive Arthritis", PrepElephant, https://prepelephant.com/topics/neet-pg/orthopaedics/psoriatic-and-reactive-arthritis

## Direct answer

Psoriatic and reactive arthritis are seronegative spondyloarthropathies that cause asymmetric, distal and enthesial joint involvement. Psoriatic arthritis accompanies psoriasis, with nail pitting and pencil-in-cup deformity, while reactive arthritis follows an enteric or urogenital infection and classically causes urethritis, conjunctivitis and arthritis. Reactive arthritis is strongly linked to HLA-B27, and both conditions respond to NSAIDs and disease-modifying drugs when they persist.

## What you must remember

- **Psoriatic pattern:** asymmetric oligoarthritis, distal interphalangeal involvement, dactylitis and enthesitis, with nail pitting and plaques as clues.
- **Dactylitis:** a diffusely swollen digit, the sausage digit, from tenosynovitis and synovitis of the whole finger.
- **Radiology:** pencil-in-cup deformity from erosion and bone proliferation at the distal joint, with fluffy periostitis and, in severe disease, ankylosis.
- **Reactive triad:** urethritis, conjunctivitis and arthritis, with keratoderma blennorrhagicum, circinate balanitis and painless oral ulcers as added features.
- **Triggers:** Salmonella, Shigella, Campylobacter and Yersinia after enteric infection, and Chlamydia trachomatis after genitourinary infection.
- **HLA-B27:** strongly associated with reactive arthritis, and linked to axial and enthesial disease across the spondyloarthropathies, though not diagnostic on its own.
- **Management:** NSAIDs for symptoms, sulfasalazine or methotrexate for persistent psoriatic arthritis, and biologics such as anti-TNF agents for severe disease after infection screening.

## Telling the two apart at the bedside

A 34-year-old man has asymmetric swelling of the knee and ankle, a painful heel and a red eye that began after a bout of diarrhoea. The task is deciding between psoriatic and reactive arthritis.

1. **Ask about the trigger.** Diarrhoea or urethritis in the preceding weeks points to reactive arthritis, while known psoriasis or nail changes point to psoriatic arthritis.
2. **Examine the skin and nails.** Plaques, scalp involvement, nail pitting and onycholysis favour psoriasis, whereas keratoderma blennorrhagicum and painless oral ulcers favour reactive arthritis.
3. **Map the joints.** Asymmetric lower limb oligoarthritis with Achilles or plantar enthesitis fits both, while distal interphalangeal involvement and dactylitis lean towards psoriatic disease.
4. **Look at the eye.** Conjunctivitis is typical of reactive arthritis, while anterior uveitis can occur in either spondyloarthropathy and needs prompt ophthalmic review.
5. **Send the tests.** Stool culture, urethral or cervical swabs for chlamydia and gonorrhoea, HLA-B27, and radiographs of the sacroiliac joints, hands and feet are obtained.
6. **Start treatment.** NSAIDs suit both, antibiotics are reserved for an identified infection, and disease-modifying drugs are used for persistent or erosive disease.

## Telling the two apart in the examination

Most traps arise from ignoring the trigger, the skin or the enthesis.

- **Trap:** treating reactive arthritis with prolonged antibiotics for the joints — **Correct:** antibiotics treat the infection and do not reliably shorten established reactive arthritis, so NSAIDs and monitoring are the mainstay.
- **Trap:** calling a sausage digit gout because the joint is asymmetric — **Correct:** diffuse swelling of a whole digit is a psoriatic or spondyloarthropathy sign, and gout does not typically produce it.
- **Trap:** using HLA-B27 as a diagnostic test — **Correct:** it is a risk association, present in many healthy people too, so diagnosis rests on the clinical pattern, the trigger and imaging.

## Frequently asked questions

### What is the pencil-in-cup deformity, and which arthritis causes it?

Pencil-in-cup deformity is a radiological change in which the end of a bone is eroded to a pointed, pencil-like shape within a widened, cup-shaped joint. It is characteristic of psoriatic arthritis and is rarely seen in other conditions.

### What are the classic features of reactive arthritis?

Reactive arthritis classically presents as urethritis, conjunctivitis and arthritis, though not every patient has all three. Keratoderma blennorrhagicum, circinate balanitis and painless oral ulcers add to the picture.

### Which organisms commonly trigger reactive arthritis?

Salmonella, Shigella, Campylobacter and Yersinia trigger reactive arthritis after an enteric infection, while Chlamydia trachomatis triggers it after a genitourinary infection. The arthritis typically begins a few weeks after the infection.

### What is dactylitis, and why does it suggest a spondyloarthropathy?

Dactylitis is diffuse swelling of an entire digit, the sausage digit, from tendon sheath and joint inflammation. It is characteristic of psoriatic arthritis and is also seen in reactive arthritis, so it favours a spondyloarthropathy over gout or osteoarthritis.

### Is antibiotic treatment useful in established reactive arthritis?

Antibiotics treat the triggering infection, such as chlamydia, but they do not reliably shorten established reactive arthritis. Joint symptoms are managed with NSAIDs and, for persistent disease, with disease-modifying drugs such as sulfasalazine.