Psoriatic Arthritis

Question 1

What is the epidemiology of psoriatic arthritis?

Answer 1

Affects between 5-25% of those with psoriasis

In 80% of cases, psoriasis precedes the arthritis

Not necessarily associated with severity of psoriasis

More common in western white populations

Most common between 35-55

Question 2

What is the aetiology of psoriatic arthritis?

Answer 2

Genetics:
- HLA-B27, B17, CW6, DR4, DR7 associations

The obvious association is the presence of psoriasis of the skin or nails
- May occasionally occur in absence or with a rash that is insignificant and unnoticed

Question 3

What is the pathophysiology of psoriatic arthritis?

Answer 3

Inflammatory arthritis affecting joints and connective tissue, tendons and sometimes entheses

Progressive with wide ranging severity
- 40-60% develop erosive and deforming joint complications

Question 4

How does psoriatic arthritis present?

Answer 4

Joint stiffness, pain, tenderness and swelling

• Can extend to whole digits i.e. a dactylitis
• Several characteristic joint presentations

Rash c.2-3yrs before arthritis in majority of cases

• Look for occult rash on scalp, extensor aspects of forearms/elbows, umbilicus and natal cleft
• Look for nail signs - pitting, yellowing, onycholysis etc

Tensosinovitis
- Tends to affect flexor rather than extensor tendons (RA often involves both)

Ocular involvement:
- Conjunctivitis - 20-30%; also associated with HLA-B27 and sacroiliitis

Tends to be relapsing and remitting

Question 5

What are the characteristic joint presentations in psoriatic arthritis?

Answer 5

Symmetrical polyarthritis

• ‘Rheumatoid pattern’
• F > M
• Wrists, hands, feet, ankles
• DIP joints rather than MCP + no skin nodules + -RF (unlike lots of RA)

Asymmetric oligoarticular arthritis:

• Hands + feet initially
• Including dactylitis
• Up to 5 joints

Lone DIP disease:

• • terminal phalanx
• Looks like an infection or traumatic ‘hammer blow’
• M > F

Arthritis mutilans:

• Relatively rare variation of DIP disease
• Resorption of terminal phalanx = ‘telescopic digit’ with ‘pencil in a cup’ XR appearance; ‘opera-glass hand’ (flexion deformity of DIP)
• M > F, early onset

Spondylitic pattern +/- sacroiliitis:

• M > F
• Morning stiffness and limitation of back movement

Juvenile onset:

• 1/5th of childhood arthritis
• Usually a monoarthritis pattern
• Simultaneous onset of rash + arthritis more common than in adults

Question 6

How do you investigate psoriatic arthritis?

Answer 6

Nothing definitive but clinical signs/Hx of rash + some testing can be useful for ruling in and out

ESR/CRP - often elevated

Synovial fluid should now show crystals; WCC usually high

HLA status interpreted with care, often by specialists

Serum IgA - raised in 2/3rds

RF - usually -ve but +ve in 5-10% of general population so should not be used to rule out

Not unusual for serum urate to be raised in acute phase

XR changes:

• Mild bony erosion
• DIP or PIP involvement
• Erosion of distal tuft of distal phalanx etc

Question 7

How do you manage psoriatic arthritis?

Answer 7

Referral to rheumatology

Drugs:

• NSAIDs
• IA steroid injection as an adjunct
• DMARDs - methotrexate etc - for those with many swollen joints, structural damage, high ESR/CRP, extra-articular manifestations
• TNF-inhibitors - etanercept, infliximab etc - considered if inadequate response to 1+ DMARD

Surgery:
- Various procedures depending on deformity etc

Physiotherapy, OT