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Mark Thomas MRPS, MGPC, BPharm, ClinDip, IP
Lead Clinical Pharmacist, Gateshead Health NHS Foundation Trust, Tyne and Wear
Psoriatic arthritis (PsA) is a chronic inflammatory joint disease that is associated with psoriasis. This condition usually affects patients who have pre-existing psoriasis. Approximately 2% of the population have psoriasis, and of these 20% of patients will go on to develop psoriatic arthritis. In patients with severe psoriasis, the prevalence of psoriatic arthritis can increase up to 40%. Men and women have an equal risk of developing this condition, with the peak onset between 20–40 years of age.1
Symptoms and presentation
Identifying the psoriasis component of this condition is usually straightforward as there are well-defined diagnostic criteria. Psoriasis typically presents as raised, bright red plaques on the skin that are covered with adherent silvery white scales. There may be a delay from the first presentation of psoriatic symptoms to the initial signs of joint dysfunction.
The common symptoms linked with PsA include:
Currently, there are no universally agreed diagnostic criteria or laboratory tests to confirm PsA. A diagnosis of PsA is made on the basis of clinical presentation suggestive of both psoriasis and inflammatory joint disease in more than one joint. The pattern of symptoms is important in confirming PsA and determining which form of the condition predominates.
Five subgroups of PsA are thought to exist. These are as follows:
Some laboratory tests may aid the diagnosis.
In patients with PsA, the erythrocyte sedimentation rate (ESR) is usually significantly raised, whereas the rheumatoid factor test is usually negative. On X-ray, there is a distinctive pattern of joint erosion that helps to distinguish between PsA and RA.
The condition is generally chronic and progressive, with erratic symptom severity including frequent flare ups and periods of remission.
Patients with active PsA have a significant risk of developing co-morbidities associated with this condition. These include diabetes mellitus, hypertension, coronary heart disease, inflammatory bowel disease, lymphoma and depression. It is important that any long-term management plan takes into account the risks of the patient developing one of these conditions and that adequate input is given from other specialists to treat them appropriately.
There are a number of tools available to assess the progression of both the psoriasis and joint dysfunction components of PsA.
The Psoriasis Area and Severity Index (PSAI) and the Dermatology Life Quality Index (DLQI) can be used to assess and monitor the progression of psoriasis. They are used as part of the criteria for the National Institute for Health and Clinical Excellence’s (NICE) guidelines for biologics in treating psoriasis.
There are a number of tools that are useful to measure the progression of symptoms in PsA. These include the American College of Rheumatology (ACR) joint count, the PsA response count (PsARC) and the European League Against Rheumatism (EULAR) response criteria.
The PsARC is designed specifically for use in PsA. This involves a four-stage assessment, including patient perception of symptoms, global physical examination, tender joint score and swollen joint score.
Treatments for PsA
The complex range of symptoms in PsA requires that the rheumatology and dermatology teams work closely in establishing an effective treatment plan for each patient. The aim of therapy is to reduce both joint pain and swelling, control symptoms of psoriasis and limit the longer-term progression of the condition. The most appropriate treatment options will vary depending upon the pattern, distribution and severity of the presenting symptoms.
Non-steroidal anti-inflammatory drugs
The usual first-line treatment is with oral non-steroidal anti-inflammatory drugs (NSAIDs). These drugs can provide effective short-term symptom relief in the initial stages of disease progression in PsA. They provide pain relief while reducing inflammation, which helps to control joint swelling and stiffness.
Often patients will experience an improvement in their symptoms with a few hours of taking NSAIDs. However, these drugs should only be used as adjuvant treatments, as they do not limit disease progression in PsA in the longer term. The lowest effective dose should be used for the shortest period to manage symptoms.1
Disease modifying anti-rheumatic drugs
In patients who present with persistent symptoms of PsA that are unresponsive to analgesia and NSAIDs, the next stage in treatment is to prescribe disease modifying anti-rheumatic drugs (DMARDs). There is some clinical evidence to support the use of methotrexate, sulfasalazine and leflunomide in the treatment of PsA.
In some cases, a combination of two DMARDs may be prescribed to control disease progression, but the aim of initial treatment is to use monotherapy to control both psoriasis and joint disease associated with PsA.
Methotrexate is usually started under the supervision of a specialist rheumatology team. It is a popular first-line DMARD in PsA, as it is effective in treating psoriatic arthritis, particularly when associated with pronounced cutaneous psoriasis. The dose is taken or given once weekly, in either tablet or injection form, in combination with folic acid supplements.
The target dose is usually the maximum dose that the patient can tolerate, following a rapid titration. The maximum dose should not exceed 25mg weekly. Methotrexate should be used within the guidelines set out by the National Patient Safety Agency (NPSA).
Sulfasalazine is considered to be a useful treatment option in PsA when the pattern of joint dysfunction is mainly restricted to the peripheral joints.
The dose should be titrated over the course of four weeks up to an initial target dose of 1g twice a day. Further dose titration is possible up to a maximum of 1.5g twice a day.
Leflunomide is the only DMARD to have a UK product licence for use in PsA. It is recommended for the treatment of active peripheral psoriatic arthritis. There is good clinical evidence for using leflunomide for this indication.
It is administered as an oral tablet and with an initial maintenance dose of 10mg daily. If tolerated, this can be titrated to a target dose of 20mg daily.
There is little clinical evidence to demonstrate the effectiveness of oral or intra-muscular gold, azathioprine or ciclosporin. These drugs are not currently recommended for the treatment of PsA.
In addition, hydroxychloroquine may occasionally be used as part of a dual therapy regime in patients who may be resistant to standard DMARD therapy and present with severe synovitis. Although not recommended for routine use in PsA, it may be prescribed with caution in PsA.
There is evidence suggesting that hydroxychloroquine can worsen the psoriasis component of the disease. Use of this drug should therefore be restricted to patients with severe joint disease and well controlled psoriasis, with regular symptom monitoring through a specialist dermatology clinic.
Choice of DMARD
There is no clinical evidence to compare the relative efficacy of the DMARDs in the treatment of PsA. Therefore, the choice of DMARD is dependant upon a range of factors, including:
Monitoring of DMARDs
All DMARDs require regular blood monitoring. This should reflect local and national guidelines, but should include:
Monitoring should be undertaken by either a specialist hospital service or as part of a community-based, shared-care arrangement.
While oral corticosteroids are not recommended for treating symptoms of PsA, there is some evidence to support the occasional use of intramuscular or intra-articular corticosteroid injections in patients who present with severe inflammatory arthropathy in specific joints.
It should be noted that overuse of parenteral corticosteroids may cause a subsequent flare up of the patient’s psoriasis and this should be considered when prescribing corticosteroids in PsA.
Anti-tumour necrosis factor (anti-TNF) drugs, such as adalimumab, etanercept or infliximab are recommended for treatment of active PsA – as defined by three or more tender joints and three or more swollen joints associated with psoriasis – in patients who have failed to respond to, are intolerant of, or have had contraindications to at least two disease modifying therapies. Treatment should be withdrawn after 12 weeks if there is not a significant, positive response as defined by the PsARC.2,3,4
Etanercept is a human TNF receptor fusion protein. It inhibits the binding of TNF-α to TNF receptors. The recommended dose is either 25mg given subcutaneously twice weekly or 50mg given subcutaneously once weekly.
Infliximab is a chimeric human-murine monoclonal antibody that inhibits the functional activity of TNF-α. Infliximab should be prescribed either in combination with methotrexate or as monotherapy in patients intolerant to methotrexate or for whom methotrexate may be contraindicated.
The recommended dose is based on 5mg/kg and so the dose prescribed will vary from patient to patient dependent upon body weight. The drug is given by intravenous infusion, and is repeated two weeks and six weeks after the initial infusion, then every eight weeks thereafter, with regular monitoring.
Adalimumab is a recombinant human monoclonal antibody. It binds specifically to TNF and neutralises its activity. The recommended dose is 40mg given by subcutaneous injection on alternate weeks.
All patients prescribed biologic therapy should be followed up and monitored via the specialist rheumatology services as defined in the national guidelines.
Treatment specific for symptoms of psoriasis
The nature of PsA means that both joint dysfunction and psoriasis need to be treated effectively.
There are a range of treatment options available to the dermatologists who manage psoriasis. These include:
For patients with psoriasis who do not gain an adequate response to first-line topical therapies, there are a range of additional treatments available, including phototherapy, retinoid tablets, methotrexate and acitretin. Should their symptoms remain unresponsive to treatment, consideration can be given to the use of biologic therapies, as per national guidelines.
Multidisciplinary team approach
Allied health professionals have a key role to play in the management of PsA. Any specialist clinical service aimed at treating patients with PsA, should have access to additional specialties including: