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Obesity-induced AA amyloidosis: A diagnosis of exclusion

Anne F. Brunger, Hans L.A. Nienhuis, Ronald W.J. van Rheenen, Mario R. Korte, Johan Bijzet, Reinold O.B. Gans & Bouke P.C. Hazenberg

A 47-year-old woman with morbid obesity (body mass index: 41 kg/m2) and a history of hypertension, pulmonary embolism and successfully treated gout (one year ago) presented with nephrotic syndrome (15 g/24 h) and loss of kidney function (endogenous creatinine clearance 27 ml/min/1.73 m2). A kidney biopsy revealed AA amyloid. An extensive investigation was performed to detect an underlying inflammatory disease process by testing blood and urine, imaging and genetic testing for autoinflammatory diseases. Serum levels of C-reactive protein (CRP) and serum amyloid A protein (SAA) were continuously elevated. Serum amyloid P component (SAP)- scintigraphy showed intense uptake in a massively enlarged liver and in the spleen. This extensive investigation did not reveal an underlying inflammatory process. Her gout became asymptomatic almost immediately after start of treatment. Therefore, we concluded that morbid obesity was the most probable cause of her AA amyloidosis. Treatment with colchicine and prednisolone did not substantially reduce the SAA and CRP levels. Also, treatment with anakinra (interleukin-1 receptor antagonist) and tocilizumab (interleukin-6 receptor antagonist) failed. The downhill course of the disease progressed to complete renal failure within three years and dialysis was started. This case indicates that the long-standing low-grade inflammation seen in morbid obesity may be a potential cause of systemic AA amyloidosis and may be difficult to treat. However, it is essentially a diagnosis of exclusion, since known underlying inflammatory conditions should be excluded first.