Synonyms: psoriatic arthropathy, arthropathia psoriatica, arthritis mutilans, seronegative arthritis associated with psoriasis

See also separate articles Psoriasis of Hands and Feet, Chronic Plaque Psoriasis, Erythrodermic Psoriasis and PUVA.

Psoriatic arthritis is an inflammatory arthritis affecting the joints and connective tissue and is associated with psoriasis of the skin or nails. Psoriatic arthritis is a progressive disorder ranging from mild synovitis to severe progressive erosive arthropathy. People with psoriatic arthritis presenting with oligoarticular disease progress to polyarticular disease and a large percentage develop joint lesions and deformities, which progress over time.¹

The disease is autoimmune-mediated with defined HLA associations (HLA-B27, -B17, -CW6, -DR4, -DR7 and others). Occasionally, it may occur in the absence of skin disease, or there may only be an insignificant rash which may not be noticed by the sufferer. Nail changes are a characteristic feature of the illness. The inflammatory process may involve the synovium and intra-articular structures, ligaments, fascial tissues and tendons (enthesopathy).

Epidemiology

The diverse clinical manifestations of this condition have impaired meaningful research on epidemiology.^2,3 The diagnosis can easily be missed or overlooked.²

Prevalence

• The prevalence of psoriasis in the general population is estimated at 2-3%. The prevalence of inflammatory arthritis in people with psoriasis is estimated at up to 30%. At least 20% of people with psoriasis have severe psoriatic arthritis with progressive joint lesions.¹
• International estimates of prevalence rates for psoriasis are about 1-3% of the population. Between 5% and 8% of these patients will suffer an associated arthropathy.⁴ Overall prevalence of psoriatic arthropathy in the white population is between 50 and 240/100,000 - that is about half as common as classical seropositive rheumatoid arthritis (RA).⁴

Risk factors

• Psoriatic arthropathy is much more common in the western white population than in other races.
• Men are more commonly affected by the spondylitic subtype, with higher incidence of the 'rheumatoid' pattern of disease among women.⁴
• It is most common in middle age (35-55) but may be seen in patients of any age.

Presentation

Psoriatic arthritis usually develops within 10 years of a diagnosis of psoriasis. The characteristics of psoriatic arthritis include joint stiffness, pain and swelling, and tenderness of the joints and surrounding ligaments and tendons. Symptoms can range from mild to very severe. The arthritis tends to be relapsing and remitting.²

• Usually the rash precedes the arthritis by a few years, but the opposite is occasionally true.
• The condition can present in those with minimal or no obvious rash. Occult rash should be looked for on the scalp, on extensor aspects of the forearms/elbows, and in the umbilicus and natal cleft.
• Some patients will only have nail changes rather than rash. Nails may show pitting, yellowing, transverse ridges or destruction (onycholysis).
• Cases where the arthritis initially affects the toes can appear very similar to gout.
• Enthesopathy affecting the Achilles tendon and plantar fascia is frequently seen. Tenosynovitis tends to affect the flexor rather than extensor tendons (both commonly affected in RA).
• Ocular involvement may be seen with conjunctivitis (20-30% of cases) and anterior uveitis (5% or so). Sacroiliitis and HLA-B27 positivity are commonly associated with ocular disease.
• Rarely, aortitis similar to that seen in ankylosing spondylitis or Reiter's syndrome and secondary amyloidosis are features of the disease.
• The presence of classical extra-articular manifestations of RA with psoriatic rash (e.g. nodules or scleritis/sicca syndrome) suggests the coincidental presence of psoriasis and RA.

Patterns of presentation

• Symmetrical polyarthritis ('rheumatoid' pattern). This is more common in women. Wrists, hands, feet and ankles are usually affected. Distal interphalangeal (DIP) joints are involved rather than metacarpophalangeal (MCP) joints, helping to distinguish it from RA, along with absence of skin nodules and a negative rheumatoid factor (RF) test.
• Asymmetric oligoarticular/pauciarticular arthritis. Hands and feet are affected initially with enthesopathy causing dactylitis ('sausage fingers'). Usually up to five joints are involved.
• Lone DIP disease. The nail and paronychial tissues can also be involved, along with the terminal phalanx, looking like an infection or traumatic 'hammer blow' appearance. This is usually seen in men.
• Arthritis mutilans. This is a relatively rare variation of DIP disease. Resorption of the terminal phalanx, giving a 'telescopic digit' appearance. It gives the classical 'pencil in cup' radiographic appearance. 'Opera-glass hand' (flexion deformity of the DIP joints), seen mainly in men with early-onset arthritis.
• Spondylitic pattern ± sacroiliitis. This is more common in men. There is morning stiffness and limitation of back movement. There may not be much in the way of symptoms, and it may be noted radiologically. Unlike ankylosing spondylitis, the vertebrae are usually affected asymmetrically and there are sometimes bizarre radiological appearances such as syndesmophytes, paravertebral ossification and fusion of vertebral bodies with calcified intervertebral discs. The atlanto-axial joint may be involved, with destruction of odontoid peg and danger of subluxation.
• Juvenile onset. This accounts for up to a fifth of childhood arthritis and usually starts as a monoarthritis, but DIP pattern may be seen. Tenosynovitis affects up to a third and nail changes are present in about two-thirds. Epiphyseal involvement can affect growth. Sacroiliitis may occur. Simultaneous onset of rash and arthritis is more common than in adults.

Differential diagnosis

See also separate articles Acute Polyarthritis and Acute Monoarthritis.

• Rheumatoid arthritis (RA).
• Reactive arthritis (Reiter's syndrome).
• Ankylosing spondylitis.
• Enteropathic arthropathy.
• Gout (particularly foot monoarthritis).
• Septic arthritis.
• Juvenile chronic arthritis and other causes of childhood arthritis.

Investigations

There are no 'clinching' confirmatory tests. Clinical and radiographic impressions are often sufficient to make the diagnosis in the presence of a classical rash.

• ESR and/or CRP will often be elevated.
• Rheumatoid factor (RF) is usually negative but 5-10% of the general population have positive RF so its presence should not be used to rule out psoriatic arthropathy.
• Other autoimmune markers such as antinuclear factor (ANF) do not have any discriminatory value.
• It is not unusual for serum urate to be elevated in the acute phase and gout may co-exist with psoriatic arthritis.
• Synovial fluid aspirate should not show evidence of any crystals, but the white cell count (predominantly neutrophils) is often significantly high.
• Serum immunoglobulin A (IgA) is elevated in about two thirds of sufferers, but must be interpreted against a background elevation affecting about one third of those with uncomplicated psoriasis.
• HLA status may aid in diagnosis but needs to be interpreted with care, usually in a secondary care setting.
• X-ray changes classically associated with psoriatic arthritis include:
  • Mild bony erosion at the edge of cartilage.
  • Asymmetric erosive changes in the small joints of the hands and feet.
  • Distal interphalangeal (DIP) or proximal interphalangeal (PIP) involvement - more common than metatarsophalangeal (MTP) or metacarpophalangeal (MCP) changes.
  • DIP cases may have erosion and deformity with bony ankylosis of the joint and subluxation.
  • Erosion of the distal tuft of the distal phalanx.
• MRI/CT scanning may be more specific and sensitive in picking up subtle signs, particularly in the hands and feet, which indicate psoriatic arthropathy but need expert interpretation. MRI is useful for imaging the sacroiliac joint to detect inflammation/deformity.

Management

All patients suspected of having psoriatic arthritis should be assessed by a rheumatologist so that an early diagnosis can be made and joint damage can be reduced.⁵

Drug

In patients with psoriasis and psoriatic arthritis, monotherapy that addresses both skin and joint disease should be used in preference to multiple therapies.⁵ Methotrexate, retinoids and psoralen combined with ultraviolet A (PUVA) treatment appear to be most effective at treating skin and joints together.⁴

• Non-steroidal anti-inflammatory drugs (NSAIDs) may be used to treat inflammation but can worsen skin condition, in which case try a different agent or class of NSAID. Indometacin is often used due to its potency but has significant gastrointestinal and renal side-effects.
• Intra-articular steroids are useful and may be used to inject periarticular structures for enthesopathy, in expert hands. Oral corticosteroids are usually avoided due to the danger of rebound exacerbation of a rash when withdrawn.⁴
• Disease-modifying antirheumatic drugs (DMARDs):
  • Should be used in patients with persistent inflammation. Treatment should be started and supervised by a specialist physician who is experienced in diagnosing and treating psoriatic arthritis.
  • Leflunomide is recommended for the treatment of active peripheral psoriatic arthritis.⁵
  • Sulfasalazine may be considered as an alternative in the treatment of peripheral psoriatic arthritis.⁵
  • Methotrexate may be considered in the treatment of psoriatic arthritis, especially when associated with significant cutaneous psoriasis.⁵
  • Antimalarial derived DMARDs such as hydroxychloroquine are usually avoided as they may cause exfoliative dermatitis, worsening psoriasis.
  • Etanercept, infliximab, adalimumab or golimumab:^1,6
    • Should be offered as an option for treating adults with psoriatic arthritis when:
      • The person has arthritis with three or more tender joints and three or more swollen joints.
      • At least two other DMARDs, given on their own or together, haven't worked.
    • If the person's psoriatic arthritis has not shown a measured response at 12 weeks, then treatment should be stopped.

Nondrug

Various surgical approaches are used to treat deformed joints for functional improvement. Chronic monoarticular synovitis can be improved by synovectomy, in combination with physiotherapy. Physical exercise helps to maintain mobility and reduce stiffness. Heat treatment aids stiffness.⁴

Complications

• These include joint destruction, finger destruction, disability, extra-articular complications such as eye disease and, rarely, aortitis (causes aortic insufficiency).
• Psoriatic arthritis can affect people's ability to work and carry out daily activities, which can have a substantial impact on quality of life.
• Atlanto-axial subluxation with attendant neurological complications can occur.

Prognosis

• Until recently, psoriatic arthritis was thought to be a mild disease. Figures suggested that severe joint deformity and destruction usually affecting the small joints of the hands and feet (called arthritis mutilans) occurred in only 5% of patients. However, more recent reports now suggest that arthritis mutilans occurs in 16% of patients. The course of psoriatic arthritis is comparable to rheumatoid arthritis, with about half of patients showing a progressive disease, eventually developing erosions and loss of function in affected joints.⁷
• People with psoriatic arthritis have a higher self-rated disease severity than those with psoriasis only. People with psoriatic arthritis have a 60% higher risk of mortality than the general population and their life expectancy is estimated to be approximately three years shorter.
• Despite clinical improvement with current disease-modifying antirheumatic drug (DMARD) treatment, joint damage has been shown radiologically in up to 47% of people with psoriatic arthritis at a median interval of two years.¹ Over time there is clinically active arthritis such that, by the time patients have been followed for more than 10 years, 55% have five or more deformed joints.²
• The condition can be disabling and cause marked joint destruction in a significant proportion of sufferers. Up to 10% may require some form of surgery for destructive deformity.⁴
• Aggressive treatment of early-stage progressive psoriatic arthritis can help to improve prognosis.¹

Prevention

Avoid prescribing lithium, oral corticosteroids, beta-blockers, antimalarials and any provoking NSAIDs, as they are known to cause exacerbations in some patients.

Document references

1. Psoriatic arthritis - etanercept, infliximab and adalimumab, NICE Technology Appraisal Guideline (August 2010); Etanercept, infliximab and adalimumab for the treatment of psoriatic arthritis
2. Gladman D D et al; Psoriatic arthritis: epidemiology, clinical features, course, and outcome. Annals of the Rheumatic Diseases, 2005
3. Veale DJ, FitzGerald O; Psoriatic arthritis--pathogenesis and epidemiology. Clin Exp Rheumatol. 2002 Nov-Dec;20(6 Suppl 28):S27-33. [abstract]
4. Al Hammadi A et al; Psoriatic Arthritis, Medscape, Mar 2011
5. Diagnosis and management of psoriasis and psoriatic arthritis in adults, Scottish Intercollegiate Guidelines Network - SIGN (October 2010)
6. Psoriatic arthritis - golimumab, NICE Technology Appraisal Guideline (April 2011); Golimumab for the treatment of psoriatic arthritis
7. Boehncke WH, Boehncke S, Schon MP; Managing comorbid disease in patients with psoriasis. BMJ. 2010 Jan 15;340:b5666. doi: 10.1136/bmj.b5666.