Less widely known but well described is the association of arthritis with the psoriasis.
In fact 5-8% of psoriasis patients develop an arthritis.
The arthritis is preceded by the rash in 70-80% of cases, but in 10 % precedes the rash.
The delay in developing the rash may be months to years. In approximately 15% the rash and arthritis appear at the same time.
The severity of the rash does not mirror the severity of the arthritis and a flare of the rash does not necessarily coincide with an arthritis flare.
Nail changes are present in 80% of patients with the arthritis versus 20% without arthritis.

The arthritis is usually seen at age 30-40’s, but it can rarely be seen in juvenile patients.
There is no sex difference in incidence.

There are five varieties of the arthritis but overlaps can occur.

1. Peripheral type - involves the distal interphalyngeal joints. 10%
2. Peripheral symmetrical polyarthritis - Similar to Rheumatoid arthritis. 25%
3. Asymmetrical joint type - asymmetrical, pauciarticular and affecting the hands, and feet, with sausage like digits. Large joints can be involved as an oligo/pauciarticular arthritis 80%
4. A spondyloarthropathy - affecting spine and sacroiliac joints. 5%-20%
5. A severe mutilating peripheral type - Arthritis mutilans.
 

Enthesitis - inflammation of tendon insertions occurs commonly, i.e. Achilles’ tendonitis.
The sausage like swelling of the digits is a common characteristic manifestation of the arthritis and is caused by dactylitis. These can be seen also in reactive arthritis.

Family history is common and should be specifically asked for by the practitioner - especially as the rash may not be present and the arthritis may appear initially as an unspecified arthritis with Rheumatoid factor negative. The suspicion of a Psoriatic arthritis would then be considered.
The genetic HLA associations include For Psoriasis alone :A1, B13, B17, Cw6. For Axial involvement - spinal type - B27, B38. For erosive disease : DR4.

Systemic involvement can occur with:

Ocular changes in 30%
Conjunctivitis
Episcleritis
Keratoconjunctivitis sicca
 

Aortic Valve disease has been described.

Because of the high skin turnover - hyperuricaemia and gout can occur coinciding with the psoriasis.

Association with HIV infection is also more recently identified with a tendency to severe rash and arthritis.

Investigations

Hematology.

Elevation of the ESR and CRP are proportional to the inflammatory process of the disease.
Rheumatoid factor is negative, but in a small percentage of the population may be elevated in an unrelated and coincidental manner.
Therefore diagnosis of Psoriatic arthritis must be made in these patients only with caution.

Radiology

Several characteristic findings are seen on XRAY.
Asymmetrical joint involvement.
Marginal erosions.
Widening of the joint margin
Erosion of the distal tufts of the digits
Subchondral erosions and development of the pencil in cup deformity
Periostitis
Osteolysis of the bone with telescoping of the digits.
Calcification of the enthesitis points with spur formation.
Sacroiliitis in some patients - often asymmetrical.
Syndesmophytes as in spondyloarthropathies.

Therapy

The therapy is based on the principal of symptomatic relief, and consideration for second line therapy. Symptomatic therapy is similar in many respects to that of the other inflammatory arthropathies, with the exception that oral steroid / cortisone is not recommended. Concern is also raised by dermatologists that steroid withdrawal may precipitate a severe skin manifestation of psoriasis - called pustular dermatitis.

Antiinflammatories remain the cornerstone of therapy and a wide assortment of these are available, and choice as to which type can be individually assessed. Analgesics for pain relief are also indicated as appropriate.

Local steroid injections ie.. triamcinolone are extremely useful for therapy of both Articular and soft tissue lesions - such as bursae, and tendonitis.

Joint protection and physical and occupational therapy are essential aspects to treatment and maintenance of function. Adequate splinting of joints - ie semi-static resting splints for the wrists ( my favorite splint here is the Futuro wrist splint), are very useful to reduce swelling and preserve function. Hydrotherapy / aquatherapy are also useful as are exercises and general rehabilitation exercise principals - determined at an individual level.

Second line therapy / Disease modifying therapy.

The choice of a second line agent is used for:
Those patients in whom the skin disease itself is severe.
Where the extent of arthritis is severe.
Erosive disease.
The function of the patient is threatened.
Symptomatic or conservative therapy is not sufficiently successful.

The choice of agents

1. Methotrexate. This is increasingly seen world-wide as the agent of choice, with starting dose 7.5 - 15 mg./ week Caution is raised regarding hepatotoxicity, and monitoring is essential. The skin and joints are shown to benefit - usually from the 2nd - 3rd week of therapy. Dose can be increased if required up to 20-30mg / week.

2. Gold Salts - either oral or injectable. This generally helps 50-75 % of patients

3. Salazopyrine (Sulphasalazine) This I find extremely useful for the spondyloarthropathy in particular, but benefit to the arthritis as well as to the skin manifestations are reported in several studies. The dose is 1g twice daily.

4. Antimalarials are generally not used as they are frequently identified with a deterioration in the psoriasis.

5. Retinoids i.e. etretinate are used mainly for the psoriasis rash, but have been shown to also relieve the arthritis. However they have a high side effect profile and can cause teratogenicity, making their use difficult in a population of patients in childbearing years. They also interestingly have been associated with development of a hypertrophic skeletal spinal disorder - DISH - diffuse idiopathic skeletal hyperostosis.

6. Cyclosporine A has also been used in resistant cases at 5mg / kg / day , with improvement at 2-4 weeks. The arthritis and skin, benefit but the disease activity returns within 6 weeks of drug withdrawal. The drug needs monitoring because of hypertension and renal problems.

7. PUVA - Photo chemotherapy (Psoralen Ultraviolet A, PUVA) PUVA treatment is of benefit for some Psoriatic arthritis patients. This benefits skin and was shown to help the peripheral ( but not the axial ) arthritis as well.

Surgery

The use of surgery may be required in the event of joint mechanical changes and the principals of surgery are the same as for Rheumatoid arthritis.