Oxalate nephropathy with a granulomatous lesion due to excessive intake of peanuts

A 65-year-old Japanese male developed renal dysfunction, showing proteinuria and marked urinary excretion of β₂-microglobulin. He had consumed approximately 100–200 g peanuts and 750–1,000 ml beer every day for two or three months. He had previously been treated for hypertension with an angiotensin-converting enzyme inhibitor, enalapril. He then visited his primary-care doctor with mild fever, and renal dysfunction with mild diabetes mellitus were diagnosed. He was referred to our hospital, and because no diabetic retinopathy was observed by ophthalmological tests, renal biopsy examination was performed to clarify renal dysfunction. Renal biopsy specimens showed intimal thickening in the small arteries and interstitial nephritis with a granulomatous lesion, accompanied by oxalate crystals under polarized light. Glomeruli were unremarkable without any immunoglobulin deposition, and nodular lesions. Because he daily consumed a large amount of peanuts, oxalate nephropathy due to excessive intake of peanuts was strongly suspected. This case revealed that unusual food habits, including nuts, can cause oxalate nephropathy, and that close examination by renal biopsy was useful for clarifying the etiology of the unknown renal damage.