About one-third of people with psoriatic arthritis have clinical enthesitis, according to results from a prospective cohort study of more than 800 patients.

Previous studies attempting to quantify enthesitis prevalence in PsA populations have found it to be as low as 8% to more than 50% of patients affected, Dr. Polachek and his colleagues noted, but such disparities can likely be attributed to the use of different enthesitis measures. To define enthesitis in the current study, the investigators used the SPondyloArthritis Research Consortium Canada (SPARCC) enthesitis index, which they called “valid and reliable, particularly for patients with PsA.”

Dr. Polachek and his colleagues detected enthesitis in 281 (35%) of 803 patents who had been recruited during 2008-2014 at a single clinic dedicated to PsA. The enthesitis diagnoses were established for at least one site on an initial visit (n = 128) or during a mean 3 years’ follow-up (n = 192).

The investigators reported that the annual incidence of enthesitis in this population was 0.9% (Arthritis Care Res. 2016 Dec 20. doi: 10.1002/acr.23174). About half of the patients in the cohort had only one site affected, and one-third had two sites affected. The most common of these sites were the Achilles tendon, plantar fascia, and the lateral epicondyle, Dr. Polachek and colleagues reported. They also found several factors associated with enthesitis: higher inflamed joint count (odds ratio, 1.06; P = .0002), less clinical damage (OR, 0.9; P = .04), more pain (OR, 1.15; P = .01), and presence of tenosynovitis (OR, 5.3; P less than .0001) or dactylitis (OR, 2.5; P = .02).

Significant risk factors for enthesitis included higher body mass index (hazard ratio, 1.04; P = .02), more actively inflamed joints (HR, 1.04; P = .0004), and younger age (HR, 0.98; P = .02). Among the patients in the cohort, 57% were male, the mean age was 50.8 years, and mean PsA disease duration was 12.3 years. Median time to resolution of enthesitis was 7.5 months, with 70% of patients improving without changes to their treatment.

The University of Toronto PsA research program receives funding from Krembil Foundation. Dr. Polachek disclosed grant funding from Janssen Canada. No other authors reported conflicts of interest.