Psoriatic arthritis

Introduction

Psoriatic arthritis is a chronic inflammatory arthritis associated with psoriasis, affecting both joints and entheses. It can lead to significant functional impairment and reduced quality of life if not diagnosed and treated promptly. Early recognition is critical to prevent irreversible joint damage and manage systemic complications.

Etiology and Risk Factors

Genetic Factors

Psoriatic arthritis has a strong genetic component. The presence of certain human leukocyte antigen (HLA) alleles, such as HLA-B27, HLA-Cw6, and HLA-B39, increases susceptibility. Family history of psoriasis or psoriatic arthritis significantly raises the risk of developing the disease.

Environmental Triggers

Environmental factors may precipitate the onset of psoriatic arthritis in genetically predisposed individuals. Common triggers include:

• Physical trauma or injury to joints or skin, known as the Koebner phenomenon
• Infections, particularly streptococcal infections, which can trigger an immune response
• Stress and lifestyle factors, such as smoking and obesity, which can influence disease severity

Immunologic Mechanisms

Psoriatic arthritis involves dysregulation of the immune system. T-cell mediated inflammation leads to overproduction of cytokines including tumor necrosis factor-alpha (TNF-α), interleukin-17 (IL-17), and interleukin-23 (IL-23). These cytokines contribute to synovial inflammation, bone erosion, and new bone formation at entheses and joints.

Pathophysiology

Inflammatory Pathways

The pathophysiology of psoriatic arthritis involves complex interactions between innate and adaptive immune responses. Activated T-cells release proinflammatory cytokines such as TNF-α, IL-17, and IL-23, which drive synovial inflammation and contribute to joint destruction. Dysregulated immune signaling also promotes angiogenesis and recruitment of inflammatory cells to affected tissues.

Joint and Enthesis Involvement

Psoriatic arthritis primarily targets the synovium and entheses, the sites where tendons and ligaments attach to bone. Enthesitis is a hallmark feature, leading to pain and swelling at these sites. Chronic inflammation results in both bone erosion and new bone formation, contributing to characteristic joint deformities and functional impairment.

Skin and Nail Manifestations

Skin and nail involvement are closely linked to joint disease in psoriatic arthritis. Psoriatic plaques, often on the scalp, elbows, and knees, can precede or follow joint symptoms. Nail changes, including pitting, onycholysis, and subungual hyperkeratosis, are common and may correlate with distal interphalangeal joint involvement.

Clinical Features

Articular Manifestations

• Peripheral Arthritis: Involves asymmetric or symmetric swelling of small and large joints, most commonly in the hands, feet, and knees.
• Axial Involvement: Inflammation of the spine and sacroiliac joints can cause back pain and stiffness, resembling spondyloarthritis.
• Dactylitis: Diffuse swelling of an entire finger or toe, often referred to as a “sausage digit.”
• Enthesitis: Tenderness at tendon or ligament insertions, commonly affecting the Achilles tendon, plantar fascia, and patellar tendons.

Extra-Articular Manifestations

• Skin and Nail Changes: Psoriatic plaques, scaling, and nail pitting or ridging.
• Ocular Involvement: Uveitis may occur, presenting with eye redness, pain, and photophobia.
• Cardiovascular and Metabolic Associations: Increased risk of hypertension, obesity, diabetes, and cardiovascular disease has been observed in patients with psoriatic arthritis.

Classification and Subtypes

Psoriatic arthritis can present in various patterns, which helps guide diagnosis and management. The main subtypes include:

• Symmetric Polyarthritis: Resembles rheumatoid arthritis with involvement of multiple joints on both sides of the body.
• Asymmetric Oligoarthritis: Involves fewer than five joints, often affecting the distal joints of the fingers or toes.
• Distal Interphalangeal Predominant: Primarily affects the distal interphalangeal joints of the hands and feet.
• Spondylitis Form: Axial involvement with inflammation of the spine and sacroiliac joints.
• Arthritis Mutilans: Severe, deforming arthritis characterized by bone resorption and joint collapse.

Diagnosis

Clinical Evaluation

Diagnosis of psoriatic arthritis relies on a combination of history, physical examination, and identification of characteristic features such as dactylitis, enthesitis, and skin or nail changes. Assessment of joint swelling, tenderness, and range of motion is essential.

Laboratory Investigations

• Inflammatory Markers: Elevated erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) may indicate active inflammation.
• Autoantibodies: Rheumatoid factor and anti-cyclic citrullinated peptide antibodies are usually negative, helping to differentiate from rheumatoid arthritis.

Imaging Studies

• X-ray Findings: May reveal joint space narrowing, bone erosion, and new bone formation at entheses.
• Ultrasound and MRI: Useful for detecting early synovitis, enthesitis, and soft tissue inflammation.
• Bone Scintigraphy: Occasionally used to assess disease activity and detect occult inflammation.

Differential Diagnosis

• Rheumatoid Arthritis
• Osteoarthritis
• Reactive Arthritis

Treatment

Non-Pharmacological Management

• Physical Therapy: Exercises to maintain joint mobility, muscle strength, and overall function.
• Occupational Therapy: Guidance on joint protection techniques and adaptive devices to reduce strain during daily activities.
• Lifestyle Modifications: Weight management, smoking cessation, and stress reduction to decrease inflammation and improve outcomes.

Pharmacological Therapy

• Nonsteroidal Anti-Inflammatory Drugs (NSAIDs): Provide symptomatic relief of pain and inflammation.
• Conventional Disease-Modifying Antirheumatic Drugs (DMARDs): Methotrexate, sulfasalazine, and leflunomide help control disease activity and prevent joint damage.
• Biologic Agents: TNF inhibitors, IL-17 inhibitors, and IL-12/23 inhibitors target specific inflammatory pathways for patients with moderate to severe disease.
• Targeted Synthetic DMARDs: Agents such as JAK inhibitors provide an oral alternative for patients who do not respond to conventional therapies.

Surgical Interventions

• Joint Replacement: Indicated in advanced joint destruction with significant functional impairment.
• Tendon or Soft Tissue Procedures: Correct deformities or relieve pain in affected joints and entheses.

Prognosis and Complications

Functional Outcomes

The long-term functional prognosis depends on early diagnosis and effective management. Delayed treatment can lead to reduced mobility, chronic pain, and limitations in daily activities.

Joint Destruction and Deformities

Persistent inflammation may result in irreversible joint damage, deformities, and arthritis mutilans in severe cases. Structural changes contribute to significant disability if not controlled.

Comorbidities

• Cardiovascular Disease: Patients have an increased risk of myocardial infarction, stroke, and atherosclerosis.
• Metabolic Syndrome: Higher prevalence of obesity, insulin resistance, and dyslipidemia is observed in psoriatic arthritis.
• Psychological Impact: Chronic pain, disability, and visible skin lesions can lead to depression, anxiety, and reduced quality of life.

Prevention and Patient Education

Early Diagnosis and Treatment

Early recognition of psoriatic arthritis is crucial to prevent irreversible joint damage. Patients with psoriasis should be regularly evaluated for joint pain, stiffness, or swelling. Prompt initiation of pharmacological therapy can control inflammation and preserve function.

Self-Management Strategies

Patients can actively participate in managing their disease through:

• Adhering to prescribed medications and treatment plans
• Engaging in regular, low-impact exercise to maintain joint mobility
• Using protective techniques to reduce joint strain during daily activities
• Monitoring for early signs of flares and seeking timely medical care

Monitoring for Comorbidities

Patients with psoriatic arthritis should undergo regular screening for associated conditions, including cardiovascular disease, metabolic syndrome, and osteoporosis. Lifestyle modifications such as maintaining a healthy weight, avoiding smoking, and following a balanced diet can reduce the risk of complications.

References

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