Published online 2020 Mar 11. doi: 10.1093/rheumatology/keaa042
Enthesitis in psoriatic arthritis (Part 3): clinical assessment and management
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k1 Rheumatology Division, Swedish Medical Center/Providence St. Joseph Health, Seattle, WA, USA
k2 University of Washington School of Medicine, Seattle, WA, USA
....The focus of this article is on the assessment of enthesitis by physical examination, the impact of enthesitis on function and quality of life, the impact of concomitant FM on clinical assessment, and the evidence for therapy of enthesitis....
Effect of central sensitization on assessment of enthesitis
Physical examination detects tenderness.
Physical examination does not discriminate between the true presence of inflammation (i.e. enthesitis) vs tenderness attributable to other factors, including what we label FM/CWP/central sensitization, which are conditions with overlapping definitions and features.
These are relatively common chronic central pain syndromes, which arise in individuals with genetic, biological and psychosocial predisposing factors and are characterized by CWP, often accompanied by fatigue, sleep disturbance and other symptoms.
These conditions occur more commonly in patients with chronic pain and inflammatory conditions.
We might use the term enthesalgia to describe this phenomenon when it influences tenderness at entheseal insertion points.
It is possible that in some individuals, tenderness is attributable only to -itis, in others only to -algia and in others, a combination of the two.
The phenomenon of coexistent central pain syndromes accompanying chronic rheumatic diseases has become an item of research and clinical importance because of its influence on disease severity measures and determination of treatment response in clinical trials and in practice.
Numerous studies of cohorts of patients with various rheumatological conditions, including RA, SLE, SS, OA, PsA and AS, have demonstrated that 15–20% of these cohorts, on average, will have a concomitant diagnosis of FM based on various classification criteria .
Brikman et al.  noted, in a Tel Aviv cohort of PsA patients, that concomitant FM was present in 18% and that all of the disease severity measures that included a subjective element reported by the patient, such as pain or patient global, such as Disease Activity in PsA (DAPSA), minimal disease activity (MDA), HAQ and LEI, were twice as severe as the same measures in patients without concomitant FM.
Højsgaard et al.  studied 69 PsA patients initiating treatment with physical and US examination of joints and entheses and also performed measures for FM/CWP, such as the widespread pain index (WPI) and Pain Detect questionnaire.
Responses consistent with FM/CWP on the WPI were seen in 35%.
These patients were not able to achieve a state of MDA, and there was little correlation between examination of joints and entheses and US findings.
These findings emphasize the importance of evaluating patients for concomitant FM/CWP in order to contextualize our assessment of disease severity and treatment response better in individual patients.