VICTORIA, B.C. – Subclinical enthesitis occurs more commonly in patients with psoriatic arthritis than in those with psoriasis, possibly as a result of age and obesity rather than disease severity, to judge from the findings of a cross-sectional study conducted by investigators at Toronto Western Hospital.
The investigators used ultrasound as well as clinical examination to assess the extent, if any, of enthesitis in study participants, who were 59 patients with psoriatic arthritis and 79 patients with psoriasis. Study participants were recruited from longitudinal cohorts. The control group was made up of 60 healthy volunteers who did not have any personal or family history of spondyloarthropathy. They were evaluated for enthesitis at sites in the calcaneus, knee, and olecranon.
Jai P. Jayakar
Findings on ultrasound – any enthesophytes, bony erosions, tendon thickness, and bursitis, within tendons – were scored using GUESS (Glasgow Ultrasound Enthesitis Scoring System), which reflects the overall burden bilaterally of enthesitis from abnormalities in five lower limb sites, and the MASEI (Madrid Sonography Enthesitis Index), which additionally includes calcifications and Doppler signals as elemental lesions as well as abnormalities of the olecranon tuberosity enthesis.
The average ages were 52, 53, and 42 years in the psoriasis, psoriatic arthritis, and healthy volunteer groups, respectively, and men accounted for 64%, 57%, and 32% of participants. Corresponding mean body mass indices were 27, 30, and 26 kg/m2, respectively.
In all, 12 anatomical sites were assessed. The mean number showing ultrasonographic enthesitis differed significantly across groups, reported study coauthor Jai P. Jayakar at the annual meeting of the Canadian Rheumatology Association. The number of anatomical sites that showed enthesitis was highest in the psoriatic arthritis group (7.1), intermediate in the psoriasis group (5), and lowest in healthy volunteers (4).
There was also a significant, graded difference across groups in GUESS scores (8.9, 5.6, and 4.4 out of a possible 36, respectively, for psoriatic arthritis, psoriasis, and healthy controls) and in MASEI scores (18.5, 9.9, and 7.7 respectively for psoriatic arthritis, psoriasis, and healthy controls out of a possible 136). However, in multivariate analyses, disease status was not associated with these scores; only increasing age and BMI showed significant associations.
"Our study is one of the first comparative assessments of subclinical enthesitis in psoriasis vs. psoriatic arthritis," noted Mr. Jayakar. "Our results reveal that the prevalence of ultrasonographic entheseal abnormalities and indices of entheseal burden ... are greater in psoriatic arthritis than in psoriasis; however, this relationship may be modulated in a multifactorial manner by factors other than disease status, such as age and body mass index.
"Now, it is possible that enthesitis could be of predictive value in specific patient subgroups – for example, age- or obesity-stratified subgroups," he added. "However, larger studies are needed to confirm the utility of subclinical enthesitis as a predictive factor for the development of psoriatic arthritis in patients with psoriasis."
How could the investigators be certain, a session attendee asked, that they were detecting disease-related enthesitis and not simply mechanical tendonitis?
That is a valid concern, given the lack of consensus among rheumatologists as to which ultrasonographic abnormalities result from degeneration, inflammation, mechanical stress, or other etiologies, acknowledged Mr. Jayakar, a medical student at the University of Western Ontario, London. Large cohorts with well-defined disease status would be required to investigate this further, he said.
"One direction in which we could move forward is if we can find specific elemental lesions – or aggregates of elemental lesions – that are of predictive value, then perhaps those could be used pragmatically to help us in our clinical management," he noted. "But as of now, the pathophysiological underpinnings of these abnormalities are not very well described."
Mr. Jayakar disclosed no relevant conflicts of interest.