Psoriatic arthritis (PsA) is inflammatory arthropathy affecting both large and small joints. PsA is seen in 1 in 5 patients with psoriasis and can occur either before, during or after the onset of psoriatic skin changes.1,2
The typical age of onset is 30-50 years old, with males and females equally affected.2
There is a strong genetic association as the majority of patients with PsA have at least one first or second degree relative with psoriasis or psoriatic arthritis.3
PsA belongs to a group of seronegative inflammatory spondyloarthropathies where the human leukocyte antigen B27 (HLA-B27) is commonly implicated.4
As PsA is a seronegative arthropathy, blood tests for rheumatoid factor (RF) and anti-cyclic citrullinated peptide (anti-CCP) are usually negative.
PsA results from an immune-mediated inflammatory response that affects the skin, joints, and periarticular structures. It tends to occur in patients with a genetic predisposition who are exposed to an environmental factor (e.g. joint trauma).
Risk factors for psoriatic arthritis include:
Personal history of psoriasis
First degree relative with psoriasis or psoriatic arthritis
History of joint trauma
Typical symptoms of psoriatic arthritis include:
Morning stiffness: greater than 30 minutes and improves over the course of the day
Constitutional symptoms: fatigue, malaise and low-grade fevers
The most common joints involved are the spine, sacroiliac joints (SIJ) and the small joints of the hands.
There are five recognised patterns of joint involvement:1
Asymmetric oligoarthritis: less than four joints affected in an asymmetrical pattern (most common)
Distal interphalangeal dominant: arthralgia of DIPs of fingers and toes with dystrophic nail changes
Symmetric polyarthritis: five or more joints affected in a symmetrical pattern
Spondylitis: inflammation of the spine including the neck, low back and SIJ
Arthritis mutilans: a rare and severe destructive arthropathy of the small joints in the hands and toes, coinciding with severe dactylitis
The following extra-articular manifestations are associated with seronegative spondyloarthropathies:
Mitral valve prolapse
Aortic root dilation
Differential diagnoses to consider in the context of psoriatic arthritis include:
Rheumatoid arthritis (RA)
Calcium pyrophosphate deposition disease (CPPD)
Relevant laboratory investigations include:
Rheumatoid factor (RF): a defining feature of PsA is seronegative blood tests, so RF positivity significantly lowers the likelihood of PsA
Anti-cyclic citrullinated peptide (anti-CCP): this finding is specific for rheumatoid arthritis, so positivity suggests RA rather than PsA
Inflammatory markers: erythrocyte sedimentation rate (ESR) and c-reactive protein (CRP) are non-specific markers that can indicate the degree of joint inflammation prognosis. They are less commonly elevated in PsA than RA.
Relevant imaging investigations include:
X-ray of affected joints: may show erosion of the small joints. Classic findings are erosions of the DIP with periarticular bone formation (osteophytes). In advanced disease, there may be “pencil in cup deformity” at the DIP
X-ray of the sacroiliac joints (SIJ): usually normal in the initial stages, but it is important to obtain a baseline radiograph for assessing disease progression
MRI of SIJ: looking for joint oedema (not routinely performed due to low specificity)
The diagnosis for PsA is a clinical diagnosis based on history and examination.
The CASPAR classification can be used to aid in the diagnosis, but it is intended for research, not clinical practice.7
The goal of management is to control joint inflammation to prevent long-term erosive changes and disability.
Management options include:
Non-steroidal anti-inflammatory drugs (NSAIDs): control inflammation and relieve pain but can take weeks to see an effect. Consider selective COX-2 inhibitors like celecoxib for those who cannot tolerate non-selective NSAIDs
Intraarticular glucocorticoid injection: reduce arthralgia but can aggravate skin symptoms (not routinely done)
Disease-modifying antirheumatic drugs (DMARDs)
Typical DMARDs used in the management of psoriatic arthritis include:
Methotrexate (MTX): an antifolate drug that is effective at treating skin lesions and peripheral joint symptoms, but less effective for axial joint symptoms. Often used first-line when multiple peripheral joints are affected.8
Biologics are monoclonal antibodies that can target specific components of the immune response to control inflammation.
Biologics used in the management of psoriatic arthritis include:
Tumour necrosis factor-alpha (TNF-a) inhibitors: an effective therapy for those who do not respond to MTX or those with axial joint symptoms
Ustekinumab (Stelara®): blocks IL-12 and IL-23 which inhibits T cell activation in an alternate inflammatory pathway to TNF-a, so considered in those who do not respond to TNF-a inhibitors
Secukinumab (Cosentyx®): blocks IL-17 in an which is another potential target for treatment affected for those who do not respond to initial therapy
Tofacitinib (Xeljanz®): JAK inhibitors are a newer class of biologics that can be considered when the initial treatment options don’t work
Pre-biologic screening tests
Patients need to be screened for underlying infections that may become reactivated when biologics are initiated.
Pre-biologic assessment should include testing for:
Tuberculosis: chest X-ray and interferon-gamma release assay (IGRA) blood test
HIV: viral serology
Hepatitis B: viral serology
Hepatitis C: viral serology
Complications of psoriatic arthritis include:
Cardiovascular disease: PsA is associated with a higher prevalence of obesity and dyslipidaemia, so patients are at an increased risk for cardiovascular disease 9
Joint erosion: those with bilateral spondylitis may show rapid joint deterioration of the hip and need arthroplasty
PsA is a seronegative inflammatory spondyloarthropathy that affects a subset of patients with psoriasis. The timing of arthritis does not always coincide with the onset of skin lesions.
There are strong genetic links as many patients have a first or second-degree relative with psoriasis or PsA. The haplotype of HLA-B27 is common to many of the seronegative spondyloarthropathies.
There are multiple known patterns in PsA affecting small joints, large joints and the axial skeleton
Enthesitis and dactylitis are hallmark findings in PsA
Diagnosis of PsA is clinical, based on history and physical examination findings and can be aided by the CASPAR criteria
The initial management includes NSAIDs, but DMARDs like methotrexate prove to be an effective drug for those with peripheral disease. Those with axial symptoms often benefit from biologics like TNF-a inhibitors, with alternate inflammatory targets should these not be effective
In the long term, patients with PsA have an increased risk of metabolic syndromes and cardiovascular disease
Dr Grainne Murphy
Dr Chris Jefferies
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Korean Academy of Rehabilitation Medicine. Modified Schober Test assessing flexion at lumbar spine. Licence: [CC BY-NC 4.0]
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Gladman, D. D., Ang, M., Su, L., Tom, B. D., Schentag, C. T., & Farewell, V. T. (2008). Cardiovascular morbidity in psoriatic arthritis. Annals of the Rheumatic Diseases, 68(7), 1131–1135.