The role of musculoskeletal ultrasound in psoriatic arthritis

Abstract

Psoriatic arthritis (PsA) may develop in up to a third of people with psoriasis and can be erosive in 40-60% of patients early on, resulting in functional impairment and reduced quality of life. In recent years with the introduction of new medications and wider use of musculoskeletal ultrasound (US) imaging in clinical practice, the possibility of earlier US diagnosis in patients with psoriasis in the pre-clinical phase of PsA has been examined. US detection of subclinical synovitis and enthesitis in psoriasis patients without musculoskeletal involvement will be discussed. The clinical spectrum of PsA is broad with five target areas of joints, tendons, entheses, skin and nails. Each domain will be discussed with their relevant US findings, focussing on synovitis, enthesitis and dactylitis. Specifically, features of enthesitis on US can be divided into those of reversible soft tissue inflammation and irreversible tissue damage. There is increasing use of US in evaluating nail involvement in psoriasis as this feature increases the probability of developing PsA. In patients with predominantly hand involvement, US enables differentiation of PsA from other inflammatory arthritides, such as rheumatoid arthritis, using specific extra-synovial US patterns of inflammation. Examples include peritenonitis of the extensor digitorum tendon at the metacarpophalangeal joints. Thickening of the flexor tendon pulleys may be predictive of PsA in the setting of early arthritis. Psoriatic related polyenthesitis without clinically swollen joints or increased inflammatory markers can mimic fibromyalgia with multiple tender points. US detection of enthesitis especially if power Doppler positive may assist by providing an objective assessment of disease activity. More recently, the Group for Research and Assessment of Psoriasis and Psoriatic Arthritis (GRAPPA) US Working Group has developed a PsA US enthesitis scoring system, addressing the elementary inflammatory and structural components and determining which entheseal sites should be scanned. The utility of US in monitoring disease activity in PsA to support clinical assessment will be discussed, including guidance in tapering therapy in clinical remission. The ongoing prospective US in PsA Treatment Study (UPSTREAM) aims to identify clinical and US predictors of treatment response in PsA. Future research should address issues such as the optimal combination for US screening of joints, tendons and entheses, the predictive value of subclinical US inflammatory lesions for future development of PsA and whether US provides any added prognostic value in PsA in those achieving minimal disease activity on therapy.