Psoriatic Arthropathy

Synonyms: Psoriatic arthritis, arthropathia psoriatica, arthritis mutilans, seronegative arthritis associated with psoriasis

See also Management of Psoriasis and PUVA therapy.

An association between psoriasis and joint disease was first noted by Bazin, a French physician, at the end of the 19th century. The link between the two conditions was not verified until the 1950s by Verna Wright, a rheumatologist practising at Harrogate spa hospital.¹ There are several manifestations of joint disease associated with psoriasis, so definitions vary, with differing diagnostic criteria. A useful overarching definition is an inflammatory arthritis associated with psoriasis, usually with a negative rheumatoid factor test (that is, a seronegative arthropathy).
The disease is autoimmune-mediated with defined HLA associations (HLA-B27, -B17, -CW6, -DR4, and -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).

The lack of diagnostic criteria for psoriatic arthropathy the diagnosis of psoriatic arthropathy until 1973, and the diverse clinical manifestations of this condition have impaired meaningful research on epidemiology.^2,1 The diagnosis can easily be missed or overlooked.¹

Prevalence

• UK prevalence of psoriasis is roughly 2,000/100,000 with equal numbers in men and women.
• Estimates of prevalence of psoriatic arthropathy are obviously lower and range from 20–100/100,000. Interestingly the M:F ratio is 1.3.³ It affects up to 10% of those with psoriasis.²
• International estimates of prevalence rates for psoriasis are about 1,000 to 3,000/100,000 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.⁴

Incidence

The reported incidence of psoriatic arthropathy has varied from 3.4 to 8 per 100 000.¹

Risk factors

• Psoriatic arthropathy is much commoner in the western white population than 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.

The arthritis tends to be relapsing and remitting.¹

Symptoms and signs

• Usually the rash precedes the arthritis by a few years, but the opposite is occasionally true.
• A family history of psoriasis may be the only clue to the aetiology of the arthritis in some cases.
• 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 forearms/elbows, in 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 akin to that seen in ankylosing spondylitis/Reiter's syndrome and secondary amyloidosis are features of the disease.
• The presence of classical extra-articular manifestations of RA with psoriatic rash (eg nodules or scleritis/sicca syndrome) suggests the co-incidental presence of psoriasis and RA.

Patterns of presentation

• Symmetrical polyarthritis ('rheumatoid' pattern) Commoner in women. Wrists, hands, feet and ankles usually affected. Distal interphalangeal (DIP) joints involved rather than metacarpophalangeal (MCP) joints, helping to distinguish from RA, along with absence of skin nodules and negative RF test.
• Asymmetric oligo/pauciarticular arthritis – Hands and feet affected initially with enthesopathy causing dactylitis ('sausage fingers'). Usually up to 5 joints involved.
• Lone DIP disease. The nail and paronychial tissues can also be involved, along with the terminal phalanx, looking like an infection or traumatic 'hammerblow' appearance. Usually seen in men.
• Arthritis mutilans. Relatively rare variation of DIP disease. Resorption of terminal phalanx giving 'telescopic digit' appearance. Gives classical 'pencil in cup' radiographic appearance. 'Opera-glass hand' (flexion deformity of DIP joints) seen mainly in men with early-onset arthritis.
• Spondylitic pattern ± sacro-ileitis. Commoner in men. Morning stiffness and limitation of back movement. May not be much in the way of symptoms, and 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. Atlantoaxial joint may be involved with destruction of odontoid peg and danger of subluxation.
• Juvenile onset. 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 commoner than in adults.

Major differential of nail changes is fungal nail infection.

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

See also acute polyarthritis and acute monoarthritis for wide differential diagnoses.

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

• ESR/CRP are often elevated.
• RF is usually negative but 5–10% may have positive RF (like the appreciable false-positive RF rate in general population) so its presence should not be used to rule out psoriatic arthropathy.
• Other autoimmune markers such as ANF do not have any discriminatory value.
• It is not unusual for serum urate to be elevated in the acute phase and indeed the two conditions may co-exist.
• Synovial fluid aspirate should not show evidence of any crystals, but white cell count (predominantly neutrophils) is often significantly high.
• Serum 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 edge of cartilage
  • Asymmetric erosive changes in small joints of hands and feet
  • DIP or PIP involvement commoner than MTP or MCP changes
  • DIP cases may have erosion and deformity with bony ankylosis of joint and subluxation
  • Erosion of distal tuft of distal phalanx
• MRI/CT may be more specific and sensitive in picking up subtle signs, particularly in hands and feet, that indicate psoriatic arthropathy but need expert interpretation. MRI is useful for imaging sacro-iliac joint to detect inflammation/deformity.

See psoriasis for details of management of skin manifestations of psoriasis. Skin disease treated concurrently with joint disease, although no strict correlation between activity of two or responsiveness to therapy.

Drug

Methotrexate, retinoids and PUVA appear most effective at treating skin and joints together.⁴

• NSAIDs may be used to treat inflammation but can worsen skin condition, in which case try a different agent or class of NSAID. Indomethacin is often used due to its potency but has significant GI and renal side effects.
• Intra-articular steroids are useful and may be used to inject peri-articular structures for enthesopathy, in expert hands.
• Disease-modifying anti-rheumatic drugs (DMARDs) should be used in patients with persistent inflammation, under expert guidance. Oral methotrexate and sulphasalazine have been shown to be effective and safe on the basis of systematic reviews.⁵ Further multicentre trials into other DMARDs are in progress, to assess safety and efficacy. Cyclosporin appears to be useful on the basis of early trials, but has significant pragmatic difficulties w.r.t. toxicity.⁴
• Drugs that modify the effect of TNF-alpha (eg soluble fusion proteins like etanercept or monoclonal antibodies such as infliximab) are under evaluation for this particular indication. NICE have issued guidance.⁶
  

  NICE guidance6,7 Etanercept 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 disease-modifying anti-rheumatic drugs (DMARDs), given on their own or together, haven’t worked. Infliximab should be offered as an option for treating adults with psoriatic arthritis if: The person meets the criteria in the two bullets above, and Etanercept causes a reaction which means that the person shouldn't continue taking it, or The person has a condition or is taking another medicine that means they should not take etanercept, or The person has major difficulty injecting themselves. Adalimumab should be offered as an option for treating adults with active and progressive psoriatic arthritis when: The person has arthritis with three or more tender joints and three or more swollen joints At least two other disease-modifying anti-rheumatic drugs (DMARDs), given on their own or together, haven’t worked. Treatment with adalimumab should be started and supervised by a specialist physician who is experienced in diagnosing and treating psoriatic arthritis. If the person’s psoriatic arthritis has not shown a measured response at 12 weeks, their treatment with etanercept or infliximab or adalimumab should be stopped.

• Anti-malarial derived DMARDs such as hydroxychloroquine are usually avoided due to their propensity to cause exfoliative dermatitis, worsening psoriasis. Oral corticosteroids are avoided due to danger of rebound exacerbation of rash when withdrawn.⁴

Non-drug

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

Moll and Wright’s description of psoriatic arthropathy suggested that the disease was less severe than that seen in RA.¹ However it has become clear that psoriatic arthropathy is much more aggressive than previously thought. About 20% of the patients develop a very destructive disabling form of arthritis. 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.¹The 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 An aggressive approach using DMARDs early in the course of severe inflammatory disease, plus the promise of response to newer agents should reduce the burden of the disease in the future. The detrimental effect on quality of life is similar to rheumatoid arthritis.¹
The following are associated with a worse prognosis and more severe disease:

• Arthritis mutilans and symmetric polyarthritis
• Young age at onset
• Severe skin involvement
• Gender (higher risk in females)
• Family history of arthritis
• HLA markers (HLA-B39 and HLA-B27 in the presence of HLA-DR7 are more likely to experience disease progression)

Significantly increased mortality is associated with:

• ESR of greater than 15 mm/h
• Medication use before the first clinical visit
• Radiological evidence of joint damage
• Absence of nail lesions

These include joint destruction, finger destruction, disability, extra-articular complications such as eye disease and rarely aortitis (causes aortic insufficiency).
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 (and can be as severe as rheumatoid arthritis).
Atlantoaxial subluxation with attendant neurological complications can occur.

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