Psoriatic Arthritis

Psoriatic arthritis (PsA) is a long-term inflammatory arthritis occurring in individuals with psoriasis, an autoimmune disease. This condition affects men and women equally and involves both genetic and environmental factors. Psoriatic arthritis can cause significant morbidity, characterised by joint inflammation and various systemic features.

Signs & Symptoms

Psoriatic arthritis commonly presents with pain, swelling, or stiffness in one or more joints. The affected joints are generally red or warm to the touch. The condition often manifests as asymmetrical oligoarthritis, affecting two to four joints within the first six months of disease onset, but can also be symmetrical in 15% of cases. The joints typically involved include the proximal and distal interphalangeal joints, metacarpophalangeal joints, and the wrist. Nail changes, such as pitting, thickening, and onycholysis, often accompany distal interphalangeal joint involvement.

Other notable symptoms include dactylitis, or sausage-like swelling of the fingers or toes, and enthesitis, particularly in the Achilles tendon or plantar fascia. Psoriatic arthritis can also lead to severe exhaustion that does not abate with rest and may progress to more destructive joint disease, such as arthritis mutilans. Early diagnosis and treatment are essential to prevent joint damage.

Causes

Psoriatic arthritis is an inheritable polygenic disease, with several genes implicated in its pathogenesis, including HLA-B*08, HLA-B*27, HLA-B*38, and HLA-B*39. Environmental factors such as obesity, severe psoriasis, nail disease, and tissue trauma can increase the risk. The exact trigger for the autoimmune response is often unknown.

Diagnosis

Diagnosing psoriatic arthritis involves a combination of clinical evaluation, health history, blood tests, and imaging studies. Features contributing to diagnosis include:

• Presence of psoriasis or a family history of psoriasis or psoriatic arthritis.
• Negative rheumatoid factor test.
• Arthritis symptoms in the distal interphalangeal joints.
• Nail pitting or onycholysis.
• Radiological evidence of degenerative joint changes.

Imaging studies like magnetic resonance imaging (MRI) can reveal signs of synovitis, enthesitis, and joint erosions.

Differential Diagnosis

Conditions that can mimic psoriatic arthritis include rheumatoid arthritis, osteoarthritis, reactive arthritis, gout, systemic lupus erythematosus, and inflammatory bowel disease-associated arthritis. Psoriatic arthritis is differentiated by features like distal interphalangeal joint involvement, nail changes, and spinal joint involvement.

Classification

Psoriatic arthritis can be classified into five main types:

1. Oligoarticular: Affects fewer than three joints and is generally mild.
2. Polyarticular: Affects five or more joints symmetrically and can be disabling.
3. Arthritis mutilans: Severe and deforming, with significant joint damage.
4. Spondyloarthritis: Characterised by stiffness in the neck or sacroiliac joint.
5. Distal interphalangeal predominant: Involves inflammation in the joints nearest the ends of fingers and toes, often with nail changes.

Treatments

Biological DMARDs

Biologics, such as TNF-α inhibitors (infliximab, etanercept, golimumab, certolizumab pegol, adalimumab) and IL-12/IL-23 inhibitors (ustekinumab), target specific parts of the immune system to control inflammation. They are administered via injection or IV infusion and may increase the risk of infections.

Nonsteroidal Anti-inflammatory Drugs (NSAIDs)

First-line medications for psoriatic arthritis include NSAIDs like ibuprofen and naproxen. These reduce pain and inflammation but can cause gastrointestinal and cardiovascular side effects.

Conventional Synthetic DMARDs

Oral medications such as methotrexate, leflunomide, and sulfasalazine help slow disease progression. They may take weeks to months to take effect and come with potential side effects like liver and kidney issues.

Phosphodiesterase-4 Inhibitors

Apremilast inhibits PDE4, reducing pro-inflammatory factors. It is taken orally and can cause side effects like headaches, nausea, and weight loss.

JAK Inhibitors

JAK1 inhibitors like tofacitinib and upadacitinib are used for active psoriatic arthritis. TYK2 inhibitors like deucravacitinib are currently undergoing clinical trials.

Other Treatments

Low-level laser therapy, photochemotherapy, corticosteroid joint injections, and orthopaedic surgery are other options for managing psoriatic arthritis symptoms and joint damage.

Epidemiology

Psoriatic arthritis affects 30% of people with psoriasis and can develop at any age, typically appearing 10 years after psoriasis onset. It is more common in Caucasians and equally affects men and women. Risk factors include severe psoriasis, nail involvement, scalp psoriasis, and a family history of PsA.

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Self-assessment MCQs (single best answer)

What is Psoriatic Arthritis (PsA)?

Which joints are commonly involved in Psoriatic Arthritis?

Which of the following is NOT a symptom of Psoriatic Arthritis?

Which genetic markers are implicated in the pathogenesis of Psoriatic Arthritis?

What is a major differential diagnosis for Psoriatic Arthritis?

Which of the following treatments is classified as a Biological DMARD?

Which of the following symptoms is characterised by inflammation at the insertion of tendons or ligaments?

What is the main distinguishing feature of Arthritis Mutilans?

Which imaging study is often used to reveal signs of synovitis, enthesitis, and joint erosions in Psoriatic Arthritis?

Which of the following is a risk factor for developing Psoriatic Arthritis?