Rheumatology: Psoriatic arthritis

Psoriatic arthritis (PSA) is severe autoimmune disease with typical presentation of a seronegative inflammatory arthritis along with features of psoriasis. It has variable presentation and can cause erosive changes and joint deformities.

Epidemiology:
2-3% of population have Psoriasis, one third of psoriasis patients will develop PSA
Male and female frequency are the same (M=F)
Bimodal, two peaks of occurence approx 25yrs and 55years. (also juvenile PSA presenting 9-12yrs)
Caucasians effected more than black or asian ethnicities
2/3 will have mild disease while 1/3 will develop severe manifestations of the disease.
Genetic and environmental factors contribute to disease
25-60% HLA-B27 positive
Link with obesity, strep pharyngitis (infections may trigger disease in those with inherited tendency) and trauma before onset.

Presentation:
Psoriasis preceded the arthritis by 8-10yrs on average
Many different presentations of psoriasis (dry itchy, sometimes painful desquamating plaques on the skin), check elbows, knees and hands. If not obvious check the scalp, behind the ear, umbilicus and nails for signs of psoriasis.
Often nail changes; nail pitting or onycholysis (loose nail), nails often thickened and discoloured.
Dactylitis is common (a sausage like swelling of toe or finger)
Often presents as an asymmetric oligoarthritis (2-4 joints effected)
there may be enthesitis (particulary the plantar fascia and achilles), fatigue, conjunctivtis (20%) and iritis (7%) also.
50% have spondyloarthropathy, presenting with lower back pain and stiffness. 20% sacroilitis
Will be Rheumatoid factor negative, and negative to most autoantibodies.
The joints will present with typical inflammatory features; swelling, effusion, erythema and heat, and will effect both small and large joints (see the different patterns below).

Diagnosis:
Seronegative arthritis and psoriasis
CASPAR criteria, 3 or more of folowing (99%sp 92%sn);
-evidence of psoriasis (current or family)
-psoriatic nail dystrophy
-negative RhF
-dactylitis
-radiographic evidence of juxtarticular new bone formation
XR can show pencil-in-cup deformity of phalanges (practically pathognomonic).
Think PSA if: involvemnet of DIPs without osteoarthritis, significant nail pitting, family history of PSA, absence of RhF positivity with polyarthritis.

Classification:
Most patients will have mild disease (2/3)
Five main presentations or subtypes:
-Asymmetric oligoarticular disease
-predominent DIP disease
-Arthritis mutilans (osteolysis of joints, mainly DIPs and PIPs with telescoping of digits)
-rheumatoid like polyarthritis (60% patients, MCPs, PIPs and wrists)
-isolated axial involvement (asymmetric sacrolilitis and jug handle syndesmophytes)

Prognosis:
Similar effect on quality of life and prognosis as rheumatoid arthritis
40-60% have erosive joint disease (deforming arthritis)
20% will develop ACR class 3 or 4 functional impairment
factors linked with poorer prognosis are; younger onset, female, acute onset, polyarticular disease and elevated CRP/ESR.
It is a lifelong disease that can flare at any point, with variable periods of remission.
Some many be clear for over 30years before a relapse.
Significant effect on quality of life.
overall mortality ratio 1.36

Treatment:
Patient should also be under the care of a dermatologist
Intial treatment with an NSAID, with addition of a DMARD if inflammation and joint pain persist.
DMARDS; sulfasalazine, azathioprine and methotrexate (most commonly used)
Steriods shuold be avoided
Treatment with biologic drugs if: peripheral arthritis with 3 or more joints tender and swollen AND have not responded to at least two standard DMARDs.
Etanercept, Infliximab, adalimumab are NICE approved. (be aware of immunosuppressive side effects and infections)
diet should be changed to a healthy diet focusing on foods that may lower inflammation; fresh fruit and veg, omega 3 acids.

Pearls and extras:

• Concordance for monozygomatic twins 35-75%, dizygomatic 12-20%
• trauma to joint is reported in 25% before onset
• arthritis and psoriasis occur simultaneously inj 33%
• no real relationshiup between tyep or pattenr of psorirasis and development of arthritis. more extensive psoriasis is linked with more deformity to a certain extent
• men tend to have a more DIP only presentation while women tend to resent iwt the polyarthritis subtype more
• pateints with DIP involvement are likely to have worse nail changes. 
• consider a concurrent HIV infection
• low titre RhF and CCA antibodies in 5% of patients
• hyperuricemia seen in 20%
• there have been anecdotable reports of 'flares' of arthritis with  hydroxychloroquine

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