This is the biopsy of a 32yo IV drug user who has nephrotic range proteinuria and MSSA bacteremia secondary to a skin abscess. What is this stain and what is your diagnosis?
The stain is an Amyloid AA immunohistochemistry and the diagnosis is AA amyloidosis involving glomeruli and arterioles. AA amyloid is usually seen in the setting of chronic inflammatory diseases and infections such as rheumatoid arthritis, ankylosing spondylitis, inflammatory bowel disease, tuberculosis, chronic osteomyelitis, and familial Mediterranean fever. It has also been described in drug users that inject drugs by a subcutaneous route (i.e., “skin popping”).
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