Tocilizumab prevented the progression of AA amyloidosis derived from adult-onset Still's disease.

Adult-onset Still's disease (AOSD) is a systemic inflammatory disease characterized by spiking fever, salmon-pink skin rash, and polyarthritis. Overproduction of interleukin (IL)-1 and IL-6 is one of the causes of AOSD, the pharmacological inhibition of which was proven to be effective. Meanwhile, uncontrolled AOSD causes several complications, such as reactive hemophagocytic lymphohistiocytosis; however, kidney involvement has been barely studied because of its rarity. We encountered a 54-year-old female with uncontrolled chronic AOSD who showed nephrotic range proteinuria, microhematuria, and rapid progressive glomerulonephritis. A kidney biopsy revealed amyloid A deposition, mes-angiolysis, crescent formation, and massive accumulation of macrophages. Steroid pulse therapy, followed by tocilizumab, a IL-6 receptor inhibitor, in combination with oral glucocorticoids dramatically improved kidney and cardiac manifestations with reduction in systemic inflammation. This case highlights the importance of regular monitoring of urinalysis in patients with AOSD, and the early recognition followed by anti-inflammatory treatment can stabilize kidney involvement.