# Renal Amyloidosis > Renal amyloidosis for NEET-SS Nephrology: Congo red birefringence, AL versus AA typing, free light chains, myeloma work-up and Indian infection-driven AA notes. - Canonical URL: https://prepelephant.com/topics/neet-ss/nephrology/amyloidosis-renal - Exam / course: NEET-SS · Subject: Nephrology - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Renal Amyloidosis", PrepElephant, https://prepelephant.com/topics/neet-ss/nephrology/amyloidosis-renal ## Direct answer Apple-green birefringence under polarised light after Congo red staining is the diagnostic moment in renal amyloidosis: beta-pleated sheet fibrils laid down in the mesangium and vessel walls, producing nephrotic-range proteinuria in kidneys that are often normal-sized or enlarged when every other chronic disease has shrunk them. What happens next depends entirely on typing, because two diseases wear the same stain. AL amyloidosis — a plasma cell disorder depositing light-chain fragments, lambda more than kappa — demands haematology with bortezomib-based chemotherapy, while AA amyloidosis deposits serum amyloid A from chronic inflammation, and in Indian practice that inflammation is still, characteristically, tuberculosis, leprosy or chronic osteomyelitis rather than the rheumatoid and inflammatory bowel disease of Western textbooks. ## What you must remember - **The stain:** Congo red, apple-green under polarised light; the fibrils are beta-pleated sheets — the chemistry behind the exam question. - **AL phenotype:** nephrotic proteinuria with restrictive cardiomyopathy, painful peripheral and autonomic neuropathy, macroglossia and periorbital purpura — the last two nearly specific and heavily tested. - **AL work-up:** serum free light chains with ratio, serum and urine electrophoresis with immunofixation, then bone marrow; NT-proBNP and troponin stage prognosis (Mayo system). - **Typing matters absolutely:** laser microdissection with mass spectrometry is the modern standard; treating AA disease with myeloma chemotherapy, or AL disease with anti-inflammatory therapy, is a catastrophic category error. - **AA causes — Indian pattern:** pulmonary and abdominal tuberculosis, lepromatous leprosy, chronic osteomyelitis and suppurative lung disease; globally, rheumatoid arthritis, inflammatory bowel disease and familial Mediterranean fever, where colchicine prevents amyloidosis outright. - **Screening biopsy:** fat pad or rectal biopsy is positive in roughly 70–80 per cent of systemic AL disease — useful when the kidney biopsy is delayed or contraindicated. - **Dialysis-related amyloidosis:** beta-2 microglobulin deposition after years on dialysis, presenting as carpal tunnel syndrome and destructive spondyloarthropathy — a distinct entity, not a variant of AL. - **Transplant caution:** AL disease recurs in the graft if the clone persists, so haematological response precedes renal listing where possible. ## Two patients, one stain, opposite treatments A 58-year-old man presents with six months of oedema: proteinuria 9 g/day, albumin 22 g/L, creatinine 1.3 mg/dL, an echocardiogram showing a thickened, restrictive left ventricle, and a tongue that fills the mouth. The kidney biopsy reports Congo-red-positive amyloid; immunofluorescence favours lambda; serum free light chains return 480 mg/L with a heavily skewed ratio. His pathway runs to haematology — bortezomib, dexamethasone and daratumumab, the ANDROMEDA backbone — with cardiac staging by NT-proBNP and troponin deciding both intensity and honesty of the prognosis conversation; his kidney survives only if the clone is silenced. Across the ward, a 40-year-old with two decades of chronic discharging osteomyelitis of the tibia has identical birefringence on biopsy and a free light chain panel that is normal. His treatment is surgical: eradicate the infection, suppress the serum amyloid A drive, and watch the proteinuria fall over months — amyloid can regress when the stimulus dies, a point the viva examiner rewards. The two biopsies are indistinguishable to the eye; the mass spectrometer and the clinic chart separate them, and every prescribing decision hangs on that separation. ## How the examiner frames it The stems are built on the discriminating signs. Nephrotic syndrome plus a giant tongue or periorbital purpura after proctoscopy or pinching — "raccoon eyes" — is AL until disproven, and the free light chain assay is the next investigation, not another biopsy. Nephrotic syndrome in a patient with chronic tuberculosis, leprosy or bronchiectasis is AA, and the exam answer is treat the underlying inflammation. The imaging twist appears regularly: kidneys that are large or normal-sized on ultrasound in a nephrotic patient nudge toward amyloidosis and myeloma, against the small kidneys of most chronic disease. One caution is worth voicing in the viva — Congo red positivity names the disease, never the type; quoting "AL until typed, by mass spectrometry where available" marks you as someone who has actually sat in a nephropathology meeting. ## Frequently asked questions ### Which stain confirms amyloid, and what is seen? Congo red with apple-green birefringence under polarised light; the fibrils are beta-pleated sheets. ### Why is typing mandatory after a positive Congo red? AL and AA amyloid share the stain but demand opposite treatments — chemotherapy for the plasma cell clone, infection or inflammation control for AA. ### What screens for AL amyloidosis? Serum free light chains with ratio, electrophoresis with immunofixation of serum and urine, and bone marrow examination; cardiac assessment by NT-proBNP, troponin and echocardiography. ### Which chronic diseases drive AA amyloidosis in India? Tuberculosis, lepromatous leprosy, chronic osteomyelitis and suppurative lung disease — infection-dominated, unlike the rheumatoid and IBD-driven pattern of Western series. ### Which organs suggest AL rather than AA at the bedside? Macroglossia, periorbital purpura, restrictive cardiomyopathy and painful autonomic neuropathy — nearly specific for AL. ### What is dialysis-related amyloidosis? Beta-2 microglobulin deposition after years on dialysis, causing carpal tunnel syndrome and arthropathy — resolved by transplantation more than by any dialysis prescription.