Psoriasis is a relapsing chronic inflammatory condition of the skin, which manifests itself in other areas such as the synovial membranes and soft tissues around many joints, eyes, heart, and blood vessels. Damage to the synovial membranes that protect the joints leads to arthritis in 5-25% patients with psoriasis.
Features of Psoriatic Arthritis
Psoriatic arthritis (PsA) is manifested in several ways:
- Enthesitis or inflammation of the soft tissue around the joints, tendons, and ligaments
- The bone and articular cartilage
A confirmed diagnosis of PsA is made when the above-said features are present in a patient with psoriasis.
PsA occurs in both genders and at all ages, but is most common between 40-50 years. In most cases, it is associated with psoriasis vulgaris, guttate psoriasis, and pustular psoriasis. While PsA occurs simultaneously with skin lesions in 10-37% of patients, arthritis precedes the skin condition in 6-18% of patients. '
It is sometimes difficult to distinguish between the clinical signs and symptoms of PsA and other spondyloarthropathies. For example, patients presenting with joint inflammation, swelling and tenderness indicate true arthritis. In some other cases, the presenting features may be isolated spinal inflammation and pain, tendinitis or enthesitis, or dactylitis. The similarity in the presenting features may hinder early diagnosis of PsA. In most cases, PsA would have resulted in joint damage by the time a confirmed diagnosis is made. This joint damage can lead to deformity and subsequent functional disability.
A history of injury or infection can also cause the onset of psoriatic skin lesions. This is called the Koebner phenomenon where lesions appear following even mild mechanical trauma such as a light scratch across the skin. In some patients, a strep infection precipitates psoriasis. In some other individuals, the trigger may be a medication, a hormonal disorder, alcohol, or smoking. Pregnancy, steroid use, and emotional stress are other potential triggers.
Bone damage may involve the axial or peripheral joints, along with nail dystrophy or enthesitis. Again, any of the clinical manifestations may occur along with other lesions or in isolation.
Signs and Symptoms
In order of frequency, the major signs and symptoms include:
- Axial inflammation (back pain): This is seen in 25-50% of PsA patients. However, it is noteworthy that in most patients who have involvement of the axial joints, there are no symptoms or signs of limited chest expansion or impaired spinal flexion for at least a decade after onset of the disease. Sacroiliac pain is found in about 32% of these patients, usually beginning on one side and becoming bilateral over time. As a patient with PsA ages, half of these patients develop sacroiliac inflammation. The earlier the PsA begins, the more is the risk of developing hip disease.
- Spondylitis (18-46%) with occasional uveitis
- Inflammation of cervical vertebrae (23-39%)
- Inflammation of thoracic vertebrae (13-21%)
In 1973, Moll and Wright suggested criteria for the diagnosis and classification of PsA. These include:
- The classic distal interphalangeal (DIP) joint involvement: This makes up for 5% of PsA cases.
- Arthritis mutilans or destructive arthritis. This produces gross deformity and disability in 5% of cases.
- Symmetric polyarthritis: This is almost identical to that of rheumatoid arthritis but is seronegative and makes up for 15% of PsA cases.
- Asymmetric polyarticular arthritis with mostly DIP and metacarpophalangeal joints, oligo- or monoarticular: This has been reported in almost 70% of PsA patients and is the most common initial presentation. The articular cartilage is thinned out, the joint space appears narrowed radiologically, and the bone surface is eroded severely resulting in a pencil-in-cup deformity and apparent widening of the joint space.
- Inflammatory spondylitis mimicking ankylosing spondylitis: This has been observed in 5% of patients.
The diagnosis of PsA or related musculoskeletal disease is dependent upon the following criteria and scores as per the PARS:
- Any of the following signs of psoriasis:
- Presence of psoriasis as confirmed by a skin or joint specialist (score 2)
- History of psoriasis from the patient, family physician, skin or joint specialist (score 1)
- Family history of psoriasis in a first- or second-degree relative, as reported by the patient (score 1)
- Current evidence of nail dystrophy due to psoriasis, characterized by onycholysis, hyperkeratosis, pitting (score 1)
- Seronegativity (rheumatoid factor negative) by ELISA or nephelometry, or any other non-latex based method, if these are not available (score 1)
- Evidence of dactylitis especially with polyarthritis and associated with enthesitis. Dactylitis is found in 32%-48% of PsA patients, mostly involving the toes (75%) or more than one digit (50%)
- Current swelling of a whole finger (score 1)
- History of dactylitis with confirmation from a rheumatologist (score 1)
- X-ray evidence of new bone formation near the affected joint
- X-ray evidence of poorly-defined ossification around the joint margins but no signs of osteophyte formation on the hands or feet (score 1)
A confirmed diagnosis of PsA is a score ≥ 3 points along with evidence of inflammation of the joints.