Psoriatic Arthritis: Current Strategies for Diagnosis and Treatment
Dr. Mease: Psoriasis occurs in 3.2% of the US population, according to current findings from the National Health and Nutrition Examination Survey.1 Of these patients with psoriasis, 10% to 30% have PSA, based on findings from recent large-scale surveys. Unfortunately, many patients with PSA are undiagnosed.
This underdiagnosis was documented in the Prevalence of Psoriatic Arthritis in Adults with Psoriasis (PREPARE) trial, during which 949 patients were assessed for plaque psoriasis in dermatology offices in North America and Europe and then were referred to rheumatologists for evaluation, regardless of their musculoskeletal symptoms.2 Of these 949 patients, 30% were diagnosed with PSA based on a careful rheumatologic exam. Of the patients diagnosed with PSA, 41% had not been given this diagnosis previously.
Part of this underdiagnosis of PSA is simply lack of knowledge and awareness among clinicians and patients that patients with psoriasis can have an arthritic condition.
Q: How can clinicians overcome these barriers to diagnosis?
Dr. Mease: The key is to seed in the minds of primary care physicians (PCPs) and dermatologists the need to ask patients with psoriasis the question, “Have you ever had problems with persistent arthritis, morning stiffness, or back pain.”
For the PCP, the first step is to distinguish between inflammatory/immunologic conditions (inflammatory arthritis, enthesitis, or ankylosing spondylitis) versus mechanical/degenerative conditions (mechanical or degenerative arthritis, tendonitis, and back pain). Mechanical/degenerative conditions are ubiquitous issues in the primary care population and PCPs and other health care providers may not necessarily take the extra step to think, “could this possibly be an immunologic inflammatory condition?” Some key factors that would indicate the possibility of PSA include the following:
- Age of onset—the younger the age, the more likely it is to be an inflammatory condition
- Persistence of pain
- Multiple sites of pain
- Prominent and prolonged morning stiffness
- Stiffness after being still for a period
In the case of back pain, a key question to ask is, “does the pain awaken you in the middle of the night?” Another key question is, “Does the pain getter better or worse with activity.” If the pain improves with activity, it raises the possibility of it being related to an inflammatory condition.
In addition, it is important for clinicians to be educated about the clinical features that can be seen in patients with PSA. For example, enthesitis is an important clinical part of PSA. Enthesitis is inflammation that occurs wherever tendons and ligaments insert into bone. Common locations include the Achilles tendon insertion at the heel, plantar fascia insertion at the heel, and patellar tendon insertions. Even the ligamentous tissue that binds the rib cage together can be inflamed, causing chest pain. Many PCPs are not aware that immunologic cells can set up inflammation right at that juncture of the ribs in patients with PSA. Enthesitis may be tougher to treat than arthritis in patients with PSA and you may need to go further up the treatment ladder to effectively treat it.
Dactylitis is another clinical condition that occurs fairly frequently in patients with PSA. In this condition, a whole digit becomes swollen and looks like a sausage. Dactylitis is highly predictive of either PSA or another spondyloarthritis condition (Figure 1).
An inflammatory spondylitis also can occur in patients with PSA. All of these conditions—arthritis, enthesitis, dactylitis, and spondylitis—can occur, depending on the individual patient. The heterogeneity of the PSA presentation is somewhat of an obstacle to making the diagnosis; on the other hand, these conditions can help the clinician make the diagnosis through pattern recognition.
Q: Are there any screening questionnaires for PSA?
Dr. Mease:Approximately 6 or 7 different screening questionnaires have been developed and validated for PSA. Examples include the following:
- Psoriasis Epidemiology Screening Tool (PEST)—This tool involves 5 simple questions. If a patient responds positively to 4 out of the 5 questions, there is a high likelihood that they have PSA (Figure 2).3
- Psoriatic Arthritis Screening and Evaluation (PASE)—A 15-item questionnaire to screen for PSA in patients with psoriasis.4
- Toronto Psoriatic Arthritis Screen (ToPAS)—An 11-item self-administered questionnaire to screen for PSA in patients with psoriasis as well as the general population.5
All of the questionnaires show high sensitivity and specificity. The problem is getting clinicians to use them.
Q: What is the typical treatment ladder for patients with PSA?
Dr. Mease: Treatment guidelines are being updated by the Group for Research and Assessment of Psoriasis and Psoriatic Arthritis (GRAPPA) and will be released in 2015.6 The previous version of these guidelines was published in 2009 and, thus, does not include recently approved agents.7
Patients seen in the primary care setting often self-treat or are prescribed nonsteroidal anti-inflammatory drugs. These agents may be helpful, especially in patients with milder manifestations of PSA.
PCPs also may prescribe a course of prednisone to treat symptoms. A caution is that there have been reports of people with psoriasis who experience a significant flare of their underlying disease once treatment with prednisone is stopped. Thus, there is a bit of an art to using steroids in patients with PSA.
For initiation of immunomodulatory treatment, referral to a rheumatologist typically is required. Methotrexate is the disease-modifying antirheumatic drug (DMARD) most commonly prescribed as first-line for the treatment of PSA. Ironically, there is no controlled trial of methotrexate in the treatment of PSA that has shown it to be an effective medication compared to placebo. The reason for this lack of evidence is mainly because only 2 or 3 trials have been performed, and none were adequately powered with respect to the number of patients studied and/or they had other limitations.
However, the practical point is that we use methotrexate often, and it works in some patients adequately as monotherapy. In other patients, methotrexate is not adequate but is partially helpful and is used in combination with a biologic agent or apremilast (Otezla), an oral agent recently approved for plaque psoriasis and PSA.