Psoriatic arthritis (PsA) is an inflammatory arthritis that occurs in up to 30% of psoriatics. It is typically considered a seronegative inflammatory arthritis, ie, without detectable rheumatoid factor. About 15% of patients develop PsA before skin psoriasis is present.

The etiology of the disease is multifactorial, with both genetic and environmental factors. PsA affects men and women equally and is predominantly seen in white individuals, similar to psoriasis.

Symptoms:

• Pain, stiffness in affected joints, with joint stiffness present for > 30 minutes in the morning (after waking) or after prolonged inactivity. Improves with activity (versus osteoarthritis / degenerative joint disease, which typically worsens with activity).
• With axial involvement – Inflammatory back pain and stiffness that improve with activity; night symptoms can cause waking from sleep; decreased range of motion of the axial spine and neck over time.
• Tender / painful; swelling at entheses (sites of tendon insertion into bone).
• Tendonitis / tenosynovitis
• Ocular inflammation may lead to scleral erythema, dry eye / foreign body sensation, or uveitis with potential visual disturbance and pain.
• Hearing loss is increased in patients with PsA.

Signs:

• Tender, painful, swollen joints with possible erythema, effusion, and warmth noted in more actively inflamed joints.
• Dactylitis – Inflammation and swelling of the entire digit including metacarpophalangeal (MCP) through proximal / distal interphalangeal (PIP/DIP) joints and intervening soft tissue, giving a "sausage digit" appearance.
• Enthesitis – Inflammation at tendinous insertion into bone, with tenderness.

Common variants:

• Distal (DIP) arthritis
• Oligoarthritis, asymmetric
• Rheumatoid arthritis (RA)-like symmetrical polyarthritis
• Arthritis mutilans – aggressive, destructive phenotype
• Axial spondylitis, sacroiliitis

Note: Patients do not necessarily fit into any one pattern and may have features of several throughout the course of illness.

Risk factors:

• Patients with nail, scalp, and inverse (intertriginous) psoriatic skin disease have a higher risk of developing PsA.
• Several genetic risk markers (HLA associations) are associated with development and variable prognosis in PsA.

Timeline:

• Progression to PsA among patients with psoriasis has been reported to occur at a rate of around 2% per year.
• Episodic flares of the disease in addition to chronic, baseline joint inflammation.
• Joint erosion / damage may accrue over time, with the potential for development of functional impairments.

Accepted CASPAR criteria (ClASsification criteria for Psoriatic ARthritis) are routinely used to classify patients with PsA for trials and studies and may also aid in diagnosis of patients. These include the presence of psoriasis skin lesions, a family history of psoriasis, nail lesions, dactylitis, absence of rheumatoid factor, and periarticular bone formation on radiographs, with a point system to grade each feature (refer to CASPAR criteria; see References).