What are the clinical features of psoriatic arthritis?

Clinical Features of Psoriatic Arthritis

Psoriatic arthritis (PsA) is an inflammatory arthropathy characterized by joint inflammation, enthesitis (inflammation at tendon/ligament insertion sites), and dactylitis ("sausage digits"), occurring in 30-33% of psoriasis patients, typically presenting between ages 30-50 years with equal sex distribution. 1

Core Musculoskeletal Manifestations

Peripheral Joint Involvement

• Inflammatory arthritis presenting with joint pain, swelling, tenderness, and early morning stiffness lasting longer than 30 minutes 1
• Distal interphalangeal (DIP) joint involvement is characteristic and distinguishes PsA from rheumatoid arthritis, where DIP involvement is uncommon 1, 2, 3
• Asymmetric oligoarthritis is common initially, though the disease becomes polyarticular over time in many patients 4, 5
• Symmetric polyarticular pattern resembling rheumatoid arthritis occurs in approximately 20% of patients, especially females, but joints are typically less tender and swollen than in RA 1, 2
• Involved joints demonstrate signs of inflammation including swelling, redness, and warmth in addition to tenderness 1

Dactylitis

• "Sausage digit" represents a combination of enthesitis of tendons and ligaments along with synovitis involving an entire digit 1
• Affects small joints of hands and feet with associated periarticular swelling 1
• This feature is pathognomonic for PsA and uncommon in rheumatoid arthritis 1, 2

Enthesitis

• Inflammation at anatomic sites where tendons, ligaments, or joint capsule fibers insert into bone 1
• Common locations include plantar fascia insertion, Achilles tendon insertion sites, and ligamentous attachments to ribs, spine, and pelvis 1, 6
• Presents with localized pain and tenderness on palpation at insertion sites 6
• This feature is pathognomonic for PsA and uncommon in rheumatoid arthritis 1, 2

Axial Involvement

• Psoriatic spondylitis affects approximately 5% of patients exclusively, with 20-50% having both spinal and peripheral joint involvement 1
• Asymmetric sacroiliitis, often asymptomatic, can be detected on imaging 1
• Spondylitis affects any level of the spine in a "skip" fashion, unlike the continuous pattern in ankylosing spondylitis 1
• Patients are less symptomatic than those with ankylosing spondylitis and seldom progress to ankylosis 1

Cutaneous and Nail Manifestations

Skin Disease Relationship

• Skin lesions precede arthritis in 72.7% of cases: 9.7% by 1 year, 15.6% by 5 years, and 47.4% by more than 5 years 1
• Arthritis precedes skin lesions in 14.9-19.4% of cases 1
• Simultaneous onset of skin and joint symptoms occurs in 16.1% of patients 1
• The severity of skin and joint disease typically do not correlate with each other 1
• Psoriatic plaques may be small or patchy, occurring in scalp or perineum, and may not be immediately apparent 5

Nail Disease

• Nail psoriasis occurs in approximately 50% of fingernails and 35% of toenails in all psoriasis patients 1
• Up to 90% of PsA patients have nail changes, making nail examination crucial for diagnosis 1, 2
• Characteristic changes include pitting, onycholysis, subungual hyperkeratosis, and the oil-drop sign 1
• Nail disease is especially common in patients with DIP joint involvement 1, 2

Disease Course and Progression

Natural History

• Mean age at presentation is 50.6 years with mean disease duration of 10.7 years 1
• Prevalence is highest in the 40-59 year age group 1
• Initially presents as oligoarticular and mild disease, but becomes polyarticular over time 4
• At least 20% of patients develop severe disease 4
• Flares and remissions characterize the disease course 1

Progressive Joint Damage

• Up to 50% of patients have an 11% annual erosion rate in the first 2 years, indicating this is not a benign condition 5
• Erosive and deforming arthritis occurs in 40-60% of patients in rheumatology referral centers 1
• Progressive joint damage may occur within the first year if untreated 2
• Permanent joint destruction can result without adequate treatment 1
• Radiographic features specific to PsA include pencil-and-cup deformity, joint space widening, gross osteolysis, and ankylosis 3

Associated Comorbidities

Systemic Complications

• Increased risk for clinical and subclinical diabetes 1
• Increased risk for cardiovascular disease and associated mortality 1, 7
• Possible association with inflammatory bowel disease 1, 8
• Uveitis may occur as an extraarticular manifestation 1, 8

Distinguishing Features from Other Arthropathies

Versus Rheumatoid Arthritis

• Presence of psoriatic plaques or nail psoriasis establishes PsA diagnosis 1, 2
• Dactylitis and enthesitis are pathognomonic for PsA and uncommon in RA 1, 2
• DIP joint involvement strongly suggests PsA, as this is uncommon in RA 1, 2
• PsA shows less symmetric distribution with joints usually less tender and swollen than RA 1, 2
• Rheumatoid factor should be negative in PsA (though 20% may have low-titer positivity) 1, 2
• Absence of rheumatoid nodules favors PsA over RA 1, 2

Versus Osteoarthritis

• Morning stiffness and stiffness after prolonged inactivity are common in PsA, whereas stiffness occurs with joint activity in osteoarthritis 1
• DIP involvement in PsA shows joint inflammation, whereas osteoarthritis shows Heberden's nodes (bone spurs) 1
• Signs of inflammation (swelling, redness, warmth) are present in PsA but absent in osteoarthritis 1

Versus Ankylosing Spondylitis

• Psoriatic spondylitis patients are often less symptomatic with asymmetric disease compared to ankylosing spondylitis 1
• Psoriatic plaques or nail changes present in psoriatic spondylitis are absent in ankylosing spondylitis 1
• PsA patients seldom have impaired mobility or progress to complete ankylosis 1

Clinical Pitfalls and Diagnostic Challenges

Common Diagnostic Errors

• Differentiating inflammatory joint pain from osteoarthritis and chronic pain syndromes (fibromyalgia) can be challenging 1
• Physical examination may help establish inflammatory arthritis if signs of inflammation are present 1
• Screening tools (Psoriasis Epidemiology Screening Tool, Toronto Psoriatic Arthritis Screen) have moderate reliability but perform less well outside their original development populations, limiting their usefulness in routine evaluation 1
• No specific serologic or genetic test is available in the United States to definitively diagnose PsA 1, 2

Critical Assessment Points

• Recurrent early morning stiffness lasting longer than 30 minutes is a valuable screening question to ask all psoriasis patients at each visit 1
• Assessment should include evaluation of all 68/66 joints (including DIP joints of hands and both proximal interphalangeal and DIP joints of feet) 1
• Radiographs and advanced imaging (MRI, CT) can detect asymptomatic axial involvement 1
• Elevated acute phase reactants (ESR, CRP) support inflammatory arthritis but are nonspecific 1, 2