3/ Although the deposits are monotypic (usually IgG1 kappa), the majority of patients do not have a detectable monoclonal paraprotein, and so far no cases associated with hematologic malignancy have been described.

2/ This entity typically presents in young females, many of which have positive autoimmune serologies but no well-defined autoimmune disease.

1/ The stain depicted is Serum Amyloid Protein (SAP) immunofluorescence. SAP has been recently described as a marker that colocalizes with IgG in cases of membranous-like glomerulopathy with masked IgG kappa deposits.

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3/ Most tophi are also associated with crystalline clefts formed by the deposition of monosodium urate (see arrow). Urate crystals are best seen in alcohol-fixed tissue or in frozen tissue sections, since most crystals dissolve after routine formalin fixation.

2/ Tophi frequently occur in the medulla, and usually consist of central regions of acellular, granular material surrounded by epithelioid macrophages, syncytial-type giant cells, and lymphocytes.

4/ It has also been seen in rheumatoid arthritis, ankylosing spondylitis, inflammatory bowel disease, tuberculosis, familial Mediterranean fever, and in drug users who inject via a subcutaneous route.

3/ Given the clinical history, the most likely subtype would be AA amyloid as this subtype is usually seen in the setting of chronic inflammatory states and infections (i.e. chronic osteomyelitis).

2/ A Congo red stain demonstrated characteristic apple-green birefringence of the material within glomeruli, interstitium, and vascular walls compatible with amyloid. By electron microscopic, the biopsy showed non-branching fibrils averaging 7-10 nm compatible with amyloid.

1/ The biopsy demonstrates non-argyrophilic material within the mesangium with extension into capillary loops within glomeruli compatible with amyloid deposition.

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The answer is: Collagen pockets

To learn more, head to our blog: www.arkanalabs.com/collagen-poc...

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