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Amyloidosis is a group of diseases characterized by the extracellular deposition of amorphous material with a fibrillar structure. Renal involvement represents the most common systemic manifestation in amyloidosis. The widely accepted classification categorizes amyloidosis based on the type of fibril-forming protein including Serum Amyloid A (AA), Immunoglobulin light chain (AL), and transthyretin (ATTR) amyloidosis. Heavy chain amyloidosis (AH) is a rare entity characterized by amyloid fibrils derived exclusively from fragments of the Ig heavy chain. To date, fewer than 15 cases have been reported. This report document a case of heavy chain amyloidosis.
Case report
Case. A 55-year-old female patient with no significant medical history was referred to a nephrologist due to proteinuria. She exhibited no other sediment alterations, renal failure or other systemic disease symptoms. Table 1 displays the laboratory results.
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A renal biopsy was performed, revealing optical microscopy results showing 21 glomeruli. Acellular mesangial PAS-positive deposit -green with trichrome- was observed in 7 glomeruli. These deposits was Congo red-positive with apple green dichroism in polarized light. Direct immunofluorescence showed light lambda chains deposits in tubular walls with no others deposits. Electron microscopy revealed podocyte processes obliteration (60%) and myofibrils measuring between 5 and 8 microns coinciding with glomerular deposits (Figure 1). Liquid chromatography tandem mass spectrometry of Congo red-positive microdissected areas confirmed a peptide profile consistent with heavy chain-type amyloid deposition.
Conclusion. Renal heavy chain amyloidosis is an exceptional and rare condition. Mass spectrometry is a pivotal diagnostic tool for amyloid typing, and its inclusion in cases with conflicting study results or cases where amyloid characterization is not possible is strongly recommended.