Dr. Amorese-O’Connell is a rheumatology fellow and Dr. Reginato is the fellowship program director and associate professor of medicine, both in the Division of Rheumatology at The Warren Alpert School of Medicine at Brown University in Providence, Rhode Island. Dr. Reginato is also the acting chief in the Division of Rheumatology at the Providence VAMC in Rhode Island. Dr. Gutierrez is an associate professor of rheumatology at the Clinica Rheumatologica, Universita Politecnica delle Marche in Jesi, Ancona, Italy, and chair, Research Direction of the Instituto Nacional de Rehabilitacion, Mexico City, Mexico.
References
Similar to RA management, US has been used to monitor disease activity and response to OA treatment. Patients who received intra-articular hyaluronic acid or intramuscular methylprednisolone for OA treatment were found to have a decrease of PD signal intensity and synovial effusion posttreatment.48 One could extrapolate these findings and conclude that US could be an additional tool for monitoring disease activity and assessing response to local and systemic treatments in OA.
Crystalline Arthropathies
Ultrasound application to crystal diseases facilitates the identification of microcrystalline deposits within the synovial membrane (joints), cartilage (both hyaline cartilage and fibrocartilage), and periarticular tissues (tendons, bursae, and soft tissues). Crystals appear as hyperechogenic spots of different sizes and shapes that can be seen in both articular and periarticular tissues. 49,50 The crystal deposition pattern on hyaline cartilage allows the differentiation between monosodium urate (MSU) and calcium pyrophosphate dehydrate (CPP) crystals. The MSU crystals are deposited at the chondrosynovial (or superficial) margin of the hyaline cartilage and described sonographically as the double contour sign in gout, whereas CPP crystals are deposited within the intermediate layer of the hyaline cartilage and are seen as hyperechoic spots frequently described as rosary beads on US. 6,49,50
Other important sites that can be evaluated to determine the presence of CPP crystals include the menisci, symphysis pubis, and triangular fibrocartilage at the wrists, hips, and shoulders. Recent EULAR recommendations have incorporated US as part of the diagnostic imaging modality for the diagnosis of CPPD and more recently for gout. 6,51 Tophi are seen as MSU precipitates deposited in the joint cavity, tendons, and/or periarticular tissues such as bursae. They can show different echogenic signal. Soft tophi can demonstrate high PD signal due to high vascularization. On the other hand, hard tophi are hyperechoic on B-mode due to the presence of calcification, which does not allow passage of US waves, creating postacoustic shadowing. 8 Studies have evaluated the predictive role of US in evaluating patients with asymptomatic hyperuricemia without any prior history of crystal-related joint disease and found tophaceous deposits in the triceps and patellar and quadriceps tendons. 52-55 Studies have also looked at using US in the assessment of treatment response to serum uratelowering therapy in patients with gout. 56,57 These studies have noted an improvement in the double contour sign, hyperechoic spots, cloudy areas in the synovial fluid, and tophus diameter and size in those patients who achieved a treat-to-target with a serum uric acid level ≤ 6 mg/dL. Patients who did not reach this target had no changes in the gout US features. 56-57 Larger cohort studies are needed to confirm these findings.
An active inflammatory process can be determined by using a PD signal in the acute gout setting with increased vascularization; however, an increased PD signal can also be seen in septic arthritis or tenosynovitis, which sometimes can coexist with crystal-induced arthritis. Therefore, diagnostic arthrocentesis, Gram stain, and culture, as well as evaluation of crystals under polarized microscopy, are still recommended.
Therapeutic Interventions
Real-time visualization of the injection needle by US allows reliable placement of the needle tip in the tissue or cavity of interest. Multiple studies have shown the low accuracy of palpation-guided injection for reaching the site of interest. 58,59 Some studies have shown a higher response rate to US-guided injections compared with palpation-guided as well as a higher rate of successful aspirations and clinical outcomes. Meta-analyses have demonstrated improved treatment response with the use of US-guided procedures compared with blinded injections. 60,61 Ultrasound-guided interventions are performed in both peripheral and axial joints. 62 The most common US-guided procedures at the VA rheumatology clinic include arthrocentesis and intra-articular corticosteroid injections of small and medium-sized joints, such as MCP joints, elbows, wrists, and ankles.
