Musculoskeletal ultrasound is an efficient, noninvasive method for evaluating inflammatory and destructive changes in bone, cartilage, tendons, ligaments, and surrounding soft tissue of patients with psoriatic arthritis. The bedside technology allows the monitoring of all peripheral joints as frequently as needed in the management of early, active disease. Power Doppler ultrasound, in particular, can estimate increases in synovium, tendon sheaths, bursae, and enthesis. Thus it provides invaluable insight into disease status and progression, according to Dr. Marwin Gutierrez, assistant professor of rheumatology at Università Politecnica delle Marche in Ancona. Italy.
Despite its value, "[ultrasound] imaging is not firmly established in the assessment of treatment efficacy and monitoring of patient outcome in daily practice," said Dr. Gutierrez. And although joint, tendon, enthesis, skin, and nail involvement has been widely described by the different subset criteria as aspects to consider in psoriatic arthritis, "ultrasound research in the disease has relatively lagged behind that of rheumatoid arthritis [RA], with scarce validated imaging outcome measures," he said.
Dr. Marwin Gutierrez
In this month’s column, Dr. Gutierrez discusses both the role of ultrasound imaging in the assessment of psoriatic arthritis (PsA) and his group’s development of a preliminary power Doppler ultrasound composite score for monitoring treatment of the disease (Rheumatology 2012 Feb. 29 [doi:10.1093/rheumatology/kes014]).
Question: What tools are currently being used for the global assessment of PsA?
Dr. Gutierrez: There are a variety of clinical instruments for measuring disease activity and treatment response in patients with PsA, including the Disease Activity Index for PsA (DAPSA), the PsA Response Criteria (PsARC), and the Disease Activity Score using 28 joint counts (DAS28), which was originally developed for patients with RA. The main weakness of the majority of these tools is that they are focused only on joint involvement and do not include measures of other key PsA targets, such as tendons, skin, and nails. Recently, the Composite Psoriatic Disease Activity Index (CPDAI) has been proposed, which includes multiple clinical domains – joints, tendons, and the spine – in its assessment. This tool provides more comprehensive information regarding disease activity, but it is limited by the absence of imaging findings, which offer a more objective measure of the global condition of the PsA patient.
Because a composite ultrasound score does not exist at present for PsA, we tested the possibility of using power Doppler ultrasound as a global measure of the inflammatory process to detect perfusion changes induced by tumor necrosis factor (TNF)-alpha antagonist, which have been shown in recent studies to be effective in improving functional outcomes and to arrest disease progression.
Question: How are the existing tools and measures insufficient? How would the power Doppler ultrasound composite score that your group has developed fill in the gaps?
Dr. Gutierrez: PsA is a chronic inflammatory disease. Its heterogeneity is such that the term "psoriatic disease" has been recently suggested to encompass the involvement at different tissue levels, including joints, tendons, enthesis, skin, and nails. Due to the high variability in the clinical course both within one patient and between patients, as well as the variability in the outcomes of PsA, no single measure can provide accurate information regarding disease activity and responsiveness in these patients.
The main disadvantage of the most commonly used clinical measures in the assessment of PsA is that they do not provide information on the real-time activity of the psoriatic disease. Rather, they provide information confined to the assessment of single domains separately. The alternative is individual evaluation of all targets. However, such an approach is associated with methodological and statistical problems, especially when these targets are employed as end points in clinical trials.
High-frequency ultrasound can detect not only structural abnormalities but also minimal blood flow changes at the superficial soft tissue level, making it a great tool for the global assessment of disease activity in psoriatic arthritis, in which persistently active disease plays a major role in causing anatomical damage and physical functional disability. Furthermore, the ability to measure global disease activity over time is important in assessing treatment efficacy in clinical trials and monitoring the patient’s course in daily care.
Additionally, pooling individual domains of disease activity into a composite ultrasound score offers a picture of disease activity along a continuous scale, and facilitates more consistency in the assessment and communication of disease activity and treatment response in research settings and clinical practice.
Question: Of the various imaging technologies, why is ultrasound the modality of choice for this application?
Dr. Gutierrez: Early detection and careful characterization of the inflammatory process in PsA play a key role in both diagnostic and therapeutic procedures. Ultrasound technology has the essential qualities to satisfy these fundamental necessities, including high- and variable-frequency probes and very sensitive power Doppler. These capabilities permit the study of structural changes with a resolution power of 0.1 mm and the sensitive detection of blood flow even in the small vessels of superficial tissues.