How Do Doctors Diagnose Psoriatic Arthritis?

Psoriatic arthritis (PsA) most often develops after psoriasis, although in a small percentage of people (10-15%), the inflammatory joint disease begins before the skin disease. Estimates vary on how many people with psoriasis develop PsA, in part because the disease presents with a wide variety of symptoms among people and diagnosis may be missed or delayed. However, the prevalence of PsA is estimated to occur in up to 40% of people with psoriasis.^1,2 PsA can occur at any age, including childhood, but most commonly appears between the ages of 30 and 50 years. It is characterized by swollen, painful, and stiff joints, ligaments, and tendons. People with psoriasis that have symptoms characteristic of PsA should be further evaluated, as early treatment is important to alleviate symptoms, prevent structural damage to the joints, and maximize quality of life.³

Who diagnoses psoriatic arthritis?

Rheumatologists, who specialize in the diagnosis and treatment of musculoskeletal disease and systemic autoimmune conditions, most often handle the diagnosis of PsA. Because most people first develop the skin condition, psoriasis, a dermatologist may be the first physician to recognize the person's symptoms as PsA.³

Evaluating psoriatic arthritis

Several areas are assessed when evaluating a patient for PsA, including:

• Peripheral joint assessment (where the doctor checks 68 joints for tenderness and 66 joints for swelling)
• Pain (which is patient reported)
• Patient assessment of disease activity
• Physical function (as measured by a health assessment questionnaire)
• Health-related quality of life
• Fatigue (which is patient reported)
• Acute phase reactants (for example, C-reactive protein or erythrocyte sedimentation rate measured by laboratory testing)

In addition, imaging is usually performed to view the affected joints.⁴

To aid in diagnosis, researchers have sought to create standardized diagnostic criteria. The most recent and well established are the Classification Criteria for Psoriatic Arthritis (CASPAR) criteria, which assess a patients’ personal and family history of psoriasis, as well as the patient’s physical symptoms of disease.^3,5

Tests performed during diagnosis of psoriatic arthritis

Several steps are used to confirm a diagnosis of PsA. Physicians perform physical exam to assess the joints and entheses, the attachment points of the ligaments and tendons. A detailed health history is also recorded. Blood tests are used to rule out rheumatoid arthritis and gout. Imaging tests, such as x-ray, ultrasound, MRI (magnetic resonance imaging) and/or CT scan (computed tomography), are often performed to evaluate the joints.^3,6

Undiagnosed psoriatic arthritis

Due to the wide variety in how PsA presents across all individuals, diagnosis of the disease can be difficult, leading to missed diagnosis or misdiagnosis. Research from the National Psoriasis Foundation indicates that nearly one in four people with psoriasis may have undiagnosed PsA. This is in addition to the 2 million people already diagnosed with the disease in the United States.⁷