19th January 2024

Psoriatic arthritis 

Background

Definition

Psoriatic arthritis is a chronic seronegative inflammatory arthritis which affects joints and connective tissue and is associated with psoriasis of the skin or nails. Psoriatic arthritis can also affect tendons, leading to dactylitis (swelling of digits) or enthesitis. It is a progressive disorder, and the presentation can range from mild synovitis to the development of severe erosive arthropathy in around 40-60% of patients.

Epidemiology

Psoriatic arthritis has been shown to affect around 20-30% of patients with psoriasis and is more common in the middle-aged Caucasian population. It correlates poorly with skin psoriasis and can often precede the development of skin symptoms. Due to the clinical heterogeneity of symptoms and the absence of skin signs in some patients, the prevalence and incidence of psoriatic arthritis may be underreported. Males and females are equally affected; however, males tend to experience an earlier onset of disease.

Causes and risk factors

The aetiology of psoriatic arthritis is unknown; however, there appears to be an increased incidence of the disease in first-degree relatives. Risk factors include family history of psoriatic arthritis, presence of HLA-B27 genotype, obesity, smoking and psoriatic nail disease. Those patients who have sustained trauma to joints or tendons, or those with a history of infections, particularly HIV, are also at increased risk for the development of psoriatic arthropathy.

Presentation 

The clinical presentation of psoriatic arthritis varies greatly, with a diverse pattern of joint involvement and dermatological features. Patients often have a large variation in disease course and outcomes and may or may not have pre-existing psoriatic skin manifestations. The disease presents most commonly in young or middle-aged adults who either have a personal or family history of psoriasis. Symptoms can vary from mild to severe, and the arthritis tends to run a relapsing and remitting course. All patients with any type of psoriasis should be reviewed annually for the development of arthritis, particularly within the first 10 years of the diagnosis of skin disease.

The hallmark feature of psoriatic arthritis is inflammatory pain, stiffness and swelling in the joints; however, other features may be present. The most commonly affected areas are the knees, ankles, hands and feet, with axial disease also occurring occasionally. The most common pattern of joint disease is monoarticular or oligoarticular with asymmetric involvement; however, polyarticular disease can occur.

Symptoms and signs

• Joint symptoms
  • Pain, tenderness, swelling in peripheral joints or axial skeleton
  • Prolonged morning stiffness longer than 30 minutes
  • Symptoms improve with activity and worsen with prolonged rest
• Dactylitis – swelling and tenderness of whole digit
• Psoriatic skin disease- red or silvery white, inflamed well-circumscribed scaly papules and plaques mostly found on extensor surfaces and the scalp
• Psoriatic nail disease
  • Pitting – shallow dents on nail
  • Oncolysis – painless separation of nail from the nail bed
• Enthesitis – mostly affecting Achilles tendon and plantar fascia
• Ocular features:
  • Conjunctivitis – most common
  • Anterior uveitis
  • Mostly seen in patients with sacroiliitis and HLA-B27 positivity
• Features of metabolic disease, e.g. hypercholesterolaemia, high blood pressure, etc

Image Source: Wikimedia Commons (2013). Psoriasis am Unterschenkel, Licensed under a creative commons licence. Available for free at:  https://commons.wikimedia.org/wiki/File:Psoriasis_am_Unterschenkel.JPG (Accessed: 30 June 2021).

Patterns of presentation

The Moll and Wright diagnostic criterion is the simplest and most often used classification system to describe the 5 main patterns of presentations in psoriatic arthritis:

1. Symmetric polyarthritis (30-40%, most common type)- symmetric polyarthritis most commonly occurs in women and can mimic the pattern seen in rheumatoid arthritis. Wrists, hands, feet, and ankles are usually affected. Factors which can help in differentiating psoriatic arthritis from rheumatoid arthritis are distal interphalangeal joint involvement rather than metacarpophalangeal joints, absence of skin nodules and absence of rheumatoid factor or anti-CCP in blood results.
2. Asymmetric oligoarthritis (20-30%)- most commonly affected areas are hands and feet, initially with enthesitis causing dactylitis (“sausage fingers”). Usually, less than 5 joints are involved.
3. Distal interphalangeal joint (DIP) arthritis (10%)- sole DIP joint involvement usually occurs in men. The nail and surrounding tissues can also be involved.
4. Arthritis mutilans (5%)- arthritis mutilans is a rare type of severe and deformative DIP disease, which gives the appearance of “telescoping fingers” due to resorption of the terminal phalanx. The classic “pencil in cup” appearance on radiographs can be seen. This is the most severe and debilitating form of psoriatic arthritis.
5. Psoriatic spondylitis with sacroiliac and spinal involvement- spondylitis most commonly occurs in men and presents with morning stiffness and limited range of back movement. Patients may be asymptomatic, and there may not be any obvious radiological findings. This can mimic ankylosing spondylitis; however, tends to affect vertebrae asymmetrically rather than symmetrically.

Image Source: Wikimedia Commons (2010). Psoriatic arthritis2010, Licensed under a creative commons licence. Available for free at: https://commons.wikimedia.org/wiki/File:Psoriatic_arthritis2010.JPG (Accessed: 30 June 2021).

Diagnosis

The diagnosis of psoriatic arthritis is clinical and is based largely on history and examination. Blood tests and imaging are performed either to establish severity of symptoms or exclude other diagnoses, particularly rheumatoid arthritis. Inflammatory joint pain and stiffness lasting more than 30 minutes, and joint or digit swelling are highly suggestive features of psoriatic arthritis in patients with pre-existing skin disease.

Investigations

Blood tests:

• ESR and CRP – can be normal or raised in polyarticular and progressive arthritis
• Rheumatoid factor – a negative result can be used to distinguish between rheumatoid arthritis and psoriatic arthritis
• Anti-CCP – useful for excluding rheumatoid arthritis (although note that anti-CCP is not always positive in RA)
• Lipid profile, fasting blood glucose and uric acid level – metabolic screen due to the increased risk of cardiovascular disease in patients with psoriatic arthritis

Imaging:

Patients who present with evidence of joint inflammation should receive plain x-rays of the hands and feet. Early disease may not produce characteristic radiological changes, and x-rays may, therefore, only reveal soft tissue swelling. The following radiological features can be demonstrated in patients with psoriatic arthritis:

• DIP joint erosions
• Joint subluxation
• Periarticular new-bone formation
• Periostitis
• Pencil-in-cup deformity: due to periarticular erosions and bone resorption in advanced disease
• Arthritis mutilans: osteolysis and articular collapse can cause “telescoping fingers” in advanced disease

MRI or CT scanning may be a more specific and sensitive method of investigating subtle psoriatic arthritis signs, especially in the hands and feet. MRI imaging of the sacroiliac joints can detect early pre-radiographic sacroiliitis, which is characteristically asymmetric and can be asymptomatic. Spinal changes tend to mostly affect the cervical spine, and subchondral bone oedema is a characteristic finding.

Other investigations:

Synovial fluid aspiration can be performed if there is a high suspicion of gout. The aspirate should not contain crystals; however, the white cell count is often high. Ultrasound of the joints can also be used to demonstrate involvement of entheses in psoriatic arthritis.

Differential diagnoses 

It can often be difficult to differentiate between psoriatic arthritis and other types of inflammatory joint disease. However, distinguishing features can include pattern of joint involvement, dactylitis, enthesitis and the absence of rheumatoid factor or anti-CCP antibodies.

• Rheumatoid arthritis (RA) – RA is an important differential diagnosis. It tends to present as a symmetric polyarthritis affecting small joints of the hands and feet. This pattern of disease can be observed in patients with psoriatic arthritis; however, these patients often have distal interphalangeal joint involvement. Dactylitis and sacroiliitis are not seen in RA, and rheumatoid factor and anti-CCP are usually positive. Hand x-rays of patients with RA would reveal osteopenia, joint space narrowing, erosions, and subluxation.
• Gout – gout usually presents with acutely swollen, warm and tender joints, and most commonly has either a monoarticular or oligoarticular pattern; however, can also affect several joints in the hands and feet, especially in the elderly. Synovial fluid examination would reveal negatively birefringent, needle-shaped crystals.
• Erosive osteoarthritis (OA) – OA often occurs in middle-aged women and affects distal and proximal interphalangeal joints of the fingers. X-rays of the hand will show characteristic changes such as osteophytes and joint space narrowing.
• Ankylosing spondylitis (AS) – some patients with psoriasis may also present with inflammatory spinal disease, which can be difficult to distinguish from AS.
• Enteric arthritis – patients with enteric arthritis would have a co-existing diagnosis of inflammatory bowel disease.
• Septic arthritis – patients with septic arthritis usually present with an acutely swollen, warm, and tender joint with systemic features such as fever. Synovial fluid culture would reveal the presence of underlying organisms.
• Reactive arthritis – reactive arthritis often presents with oligoarthritis, usually in weight-bearing joints and can also include dactylitis and enthesitis. However, there may often be a history of preceding gastrointestinal or genitourinary infection, and features such as conjunctivitis and urethritis may also be present. X-rays may show soft tissue swelling.
• Mycobacterial tenosynovitis – patients with mycobacterium tuberculosis and atypical mycobacteria may also present with dactylitis; however, synovial biopsy and culture would reveal the underlying organisms in these cases
• Sarcoid dactylitis – chronic sarcoidosis can also present with dactylitis, but patients will often have other features suggestive of underlying sarcoid, e.g., lymphadenopathy, respiratory symptoms. Chest x-ray may reveal hilar lymphadenopathy, and serum ACE levels may be raised.

Management

Non-pharmacological management

All patients with suspected psoriatic arthritis should be referred to a rheumatologist for assessment and management. Non-pharmacological therapies include physiotherapy, exercise, and optimization of metabolic risk factors such as smoking cessation and weight loss.

Pharmacological management

In patients with a combination of psoriatic arthritis and psoriasis, monotherapy, which can adequately treat skin and joint disease, is preferred. The European League Against Rheumatism (EULAR) guidelines recommend progression of therapies to achieve adequate disease control and individualised treatment plans.

• Non-steroidal anti-inflammatories (NSAIDs): NSAIDs can be used for symptomatic relief and may even be sufficient for patients with limited disease (i.e., monoarthritis, oligoarthritis and absence of joint erosions). An adequate trial consists of 6-12 weeks of at least 2 NSAIDs. If this does not produce a sufficient improvement in symptoms, other therapies are considered.
• Corticosteroid injections: Intra-articular steroid injections can be used as adjunctive therapy if response to NSAIDs is inadequate. Systemic steroids should be avoided due to the risk of rebound worsening of skin disease once withdrawn.
• Conventional disease-modifying anti-rheumatic drugs (DMARDs): Conventional DMARDs such as Methotrexate, Sulfasalazine or Leflunomide should be considered at an early stage in patients with multiple affected joints, structural damage, raised inflammatory markers and extra-articular manifestations. Methotrexate is often given first line due to ease of administration and rapid onset of action. Hydroxychloroquine should be avoided due to risk of worsening psoriasis. Conventional DMARDs, however, are only used for peripheral arthritis, as they have not been shown to have any benefit in treating axial disease.
• Biological disease-modifying anti-rheumatic drugs (DMARDs): Anti-TNF drugs such as Etanercept, Infliximab, Adalimumab or Golimumab can be offered in patients presenting with arthritis and three or more tender or swollen joints, when at least two other DMARDs have not produced a sufficient response. They are also considered for patients who present with progressive axial disease despite receiving an adequate course of treatment with at least 2 NSAIDs. If there is no response after 12 weeks of receiving a biological agent, treatment should be stopped. Other drugs which can be used if anti-TNF medications are contraindicated include Ustekinumab (human monoclonal antibody which inhibits receptor binding of interleukin 12 and interleukin 23), Secukinumab (monoclonal antibody to interleukin 17) and Apremilast (oral phosphodiesterase-4 inhibitor).

Summary of the management of psoriatic arthritis, adapted from BMJ Best Practice: Psoriatic Arthritis [Internet] Bestpractice.BMJ.com [cited June 2022]. Available from: https://bestpractice.bmj.com/topics/en-gb/524/management-approach

References 

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