Later Criteria
For the 30 years or so after their 1973 paper, almost all published studies of psoriatic arthritis used the criteria established by Moll and Wright: Psoriasis associated with inflammatory polyarthritis, usually with a negative serological test for rheumatoid factor.7 Moll and Wright seem to have designed their definition to be sensitive without being overly specific. However, some researchers believe that, in practice, Moll and Wright may have used other more specific disease features (such as dactylitis and enthesitis) to make their clinical diagnoses, even though these were not specifically included in their disease definition itself.7 In other words, Moll and Wright may have not intended for their definition to be used as strict clinical criteria in the modern sense.
Later researchers have sometimes differed in their interpretations of the definitions and clinical subgroup descriptions presented in Moll and Wright’s paper and may have over-interpreted the paper’s disease definition as an absolute criteria. Eventually, this led to some criticisms of what became known as the Moll and Wright criteria, and several attempts were made to establish other diagnostic criteria that could be expected to perform more reliably in clinical trials. These new criteria were developed to add specificity to the disease criteria, usually adding some feature that also resulted in reduced sensitivity.14
Dr. Espinoza and colleagues actually put forth one set of these new proposed criteria. “Together with Frank Vasey, my close associate and collaborator years back, we realized the inclusion of skin and/or nail involvement and imaging studies of sacroiliac joints would render any classification criteria more sensitive and specific,” he explains. “This assumption was proven correct years later, although we did not validate our proposed criteria.”
Eventually the CASPAR criteria were established in 2006, based on data from the Classification of Psoriatic Arthritis study group. According to CASPAR, to achieve a formal diagnosis of psoriatic arthritis a patient must exhibit inflammatory articular disease of the joint, spine or enthesis. In addition, patients must have at least three of the following:
- Present or past psoriasis or family history of psoriasis (only one additional item is needed if the patient currently has psoriasis)15
- Psoriatic nail dystrophy;
- Current or past dactylitis;
- Radiological evidence of psoriatic arthritis; and/or
- Negative rheumatoid factor test.
Dr. Espinoza notes these criteria are now widely used both at the clinical level and for clinical trials. “CASPAR has been validated, and it performs well across ethnic groups, and in early and chronic disease. It meshes well with current therapeutic guidelines for psoriatic arthritis.”
Phase 3 trials currently require patients meet CASPAR criteria for inclusion. But Dr. Ritchlin draws a distinction between these types of criteria and looser diagnostic criteria. “They don’t equal diagnostic criteria, because diagnosis is really based on clinical judgment.”
In other words, a patient might have incomplete criteria via CASPAR for inclusion in a psoriatic arthritis trial, but enough characteristics for clinical diagnosis.
“When you are talking about diagnosis in a clinical setting, it’s more clinical judgment,” he adds. “Some people will use the CASPAR criteria. Some people will use the Moll and Wright, which is much broader, so if they see a patient with inflammatory arthritis and psoriasis, they may diagnosis them with psoriatic arthritis. Others may require the presence of dactylitis or X-ray changes. So it ranges across the spectrum as to how these patients are diagnosed.”
Although strict Moll and Wright criteria are no longer used in a research setting, the importance of their comprehensive disease description still stands out. The pair’s landmark clinical synthesis ultimately made possible further refinements, categorization and research progress on the disease.