Intraarticular corticosteroid injections are an effective short-term treatment for symptomatic knee OA compared to placebo. Patients with noninflammatory characteristics on ultrasound had a more prolonged benefit from IA corticosteroids compared to inflammatory patients.

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The patient, a 57-year-old man, presented to the hospital with right-sided pleuritic chest pain, dyspnea on exertion, and lower extremity edema. He was found to have a large pericardial effusion with early tamponade on echocardiography. Pericardiocentesis yielded 900 ml of serosanguineous fluid. Soon after, he developed epigastric pain. A computed tomography scan of the abdomen revealed diffuse inflammation of the retroperitoneal spaces, a rim of attenuation surrounding the aorta (A, short arrows), and a perirenal infiltrative process involving both kidneys and giving a hairy kidney appearance (A, long arrows). The differential diagnosis of a hairy kidney includes lymphoma, sarcoidosis, and Erdheim-Chester disease (ECD) (1). Knowing that ECD can affect long bones, we obtained radiographs of the femur, which revealed diffuse sclerotic foci and mild cortical thickening (B) (2). A biopsy of the femur showed sclerotic bone with histiocytoid marrow infiltrates. Further staining was positive for CD68, lysozyme, and CD163, consistent with ECD. An immunohistochemical stain was positive for BRAF V600E mutation. Vemurafenib was started, and 4 months later, a repeat positron emission tomography scan showed a vast improvement in his disease burden. ECD is a non-Langerhans histiocytic disease that affects multiple body systems. What was once a rare disease is now becoming more frequently identified as we learn more about its histopathology. ECD is of particular interest to rheumatologists because it can mimic large vessel vasculitis given that ECD can present with a thickened or coated aorta. The pathogenesis of ECD is derived from a malignancy of myeloid progenitor cells that undergo a BRAF mutation, which is typically V600E. This mutation makes it amenable to treatment with BRAF kinase inhibitors, such as vemurafenib and dabrafenib. However other treatments, such as interferon-α, interleukin 1 inhibitors, and tumor necrosis factor inhibitors, have been used as well.Author disclosures are available at https://onlinelibrary.wiley.com/action/downloadSupplement?doi=10.1002%2Facr2.11392& file=acr211392-sup-0001-Disclosureform.pdf.