Amyloidosis and monoclonal gammopathy of renal significance

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Renal amyloid and MGRS overlap but are not interchangeable. AL amyloid is one MGRS lesion when produced by a small clone, while MGRS also includes monoclonal immunoglobulin deposition disease, proliferative glomerulonephritis with monoclonal deposits, light-chain proximal tubulopathy, immunotactoid disease and complement-associated patterns linked to a clone. Lesion identification, not paraprotein size, establishes renal significance.

The clinical range spans asymptomatic proteinuria to nephrotic oedema, Fanconi syndrome and rapidly progressive kidney dysfunction. Extrarenal clues include restrictive cardiomyopathy, orthostatic hypotension, peripheral or autonomic neuropathy, macroglossia, periorbital purpura, hepatomegaly and unexplained weight loss. Their absence does not exclude renal-limited monoclonal injury.

Diagnostic safety depends on matching three components: renal pathology, precise deposited-protein or immunoglobulin typing, and clone identification. Treatment is then clone-directed even when marrow burden is modest, because preserving kidney function is the indication. Regimens change quickly and are modified for renal and cardiac function; they must come from the current haematology pathway rather than a generic chemotherapy schedule.

Key points

Amyloidosis is extracellular deposition of misfolded fibrils; renal AL amyloid commonly causes albumin-predominant proteinuria, nephrotic syndrome and progressive kidney impairment.
MGRS describes kidney injury caused by a monoclonal immunoglobulin from a B-cell or plasma-cell clone that may be too small to meet conventional malignancy treatment criteria.
A small paraprotein is not necessarily incidental when renal biopsy demonstrates a compatible monoclonal lesion.
Use serum and urine immunofixation plus serum free light chains, interpreting the ratio in the context of reduced renal clearance; electrophoresis alone can miss disease.
Congo-red positivity establishes amyloid, but the fibril protein must be typed because AL, AA, transthyretin and hereditary forms have different treatments.
Kidney biopsy requires light microscopy, immunofluorescence and electron microscopy; mass-spectrometry typing or expert review is valuable when staining is uncertain.
AL amyloidosis is systemic until shown otherwise, so cardiac biomarkers and organ staging are urgent because cardiac involvement strongly shapes tolerance and prognosis.
Treatment targets the clone or inflammatory precursor rather than the proteinuria alone and should be planned jointly by nephrology, haematology and the relevant specialist service.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

AL amyloid

A plasma-cell or B-cell clone produces misfolded immunoglobulin light chains that form amyloid fibrils, even when the clonal burden is below conventional malignancy criteria.

Non-AL amyloid

Persistent inflammatory disease can generate AA amyloid, while transthyretin and hereditary precursor proteins produce other systemic forms requiring different diagnostic and treatment pathways.

Non-amyloid MGRS lesions

Small monoclonal clones can cause immunoglobulin deposition disease, proliferative glomerulonephritis, light-chain proximal tubulopathy or complement-associated lesions without forming amyloid fibrils.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Pathogenic protein production
A clonal, inflammatory or inherited source produces a precursor protein prone to misfolding, aggregation or tissue-specific immunoglobulin deposition.
2
Glomerular deposition
Amyloid fibrils or other monoclonal deposits disrupt renal filtration, commonly producing albumin-predominant proteinuria, nephrotic syndrome and progressive kidney impairment.
3
Proximal tubular injury
Selected monoclonal proteins injure proximal tubules, producing Fanconi features such as glycosuria, phosphate wasting, acidosis or hypouricaemia rather than a purely nephrotic phenotype.
4
Progressive organ dysfunction
Persistent amyloid or monoclonal injury can worsen kidney function, while systemic disease may also affect cardiac, neurological, hepatic and autonomic function.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Nephrotic amyloid phenotype

Heavy albuminuria, oedema and low albumin may occur with relatively bland urine sediment and initially preserved filtration.

Cardiac amyloid signalRed flag

Breathlessness, syncope, raised biomarkers, low-voltage ECG or increased ventricular wall thickness may indicate high-risk cardiac involvement.

Monoclonal tubular injury

Glycosuria without marked hyperglycaemia, phosphate wasting, acidosis or hypouricaemia can reveal light-chain proximal tubulopathy.

Myeloma-related emergencyRed flag

Abrupt acute kidney injury, hypercalcaemia, anaemia, bone pain or infection requires expedited haematology and nephrology assessment.

Systemic deposition clues

Purpura, macroglossia, neuropathy, autonomic symptoms, hepatomegaly or unexplained weight loss should broaden organ staging.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
Serum free light chains with serum and urine immunofixationFirst step
Why
Detect and characterise a monoclonal immunoglobulin with greater sensitivity than electrophoresis alone.
Interpretation and limitations
Reduced GFR alters absolute light-chain concentrations and the expected ratio; marked involved-chain excess or rapid change remains concerning and needs haematology interpretation.
02
Quantitative urine protein and albumin
Why
Define glomerular versus non-albumin protein loss and establish renal burden.
Interpretation and limitations
Disproportionately low ACR relative to total protein can suggest filtered light chains or tubular protein, whereas amyloid often produces albumin-predominant nephrosis.
03
Kidney or other tissue biopsy with Congo red and typing
Why
Prove amyloid or another monoclonal renal lesion and identify the deposited material.
Interpretation and limitations
Apple-green birefringence supports amyloid, but immunostaining or proteomic typing is required; morphology and clonality must agree before treatment attribution.
04
Bone marrow and clone-directed studies
Why
Identify the plasma-cell or B-cell source after a renal lesion is established or strongly suspected.
Interpretation and limitations
A small marrow clone may still be causative; absence of classic myeloma burden does not negate MGRS.
05
Cardiac and systemic organ staging
Why
Determine urgency, prognosis and safe treatment intensity in suspected AL amyloidosis.
Interpretation and limitations
Use ECG, echocardiography, troponin, natriuretic peptide and further imaging through specialist pathways; renal failure itself can elevate biomarkers, requiring expert synthesis.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Diabetic kidney disease

Longstanding diabetes with typical microvascular disease and gradual albuminuria supports diabetic nephropathy; paraprotein, systemic deposition clues or atypical progression should prompt biopsy-led reassessment.

Membranous nephropathy

Both may produce bland nephrotic urine, but anti-PLA2R testing and subepithelial immune deposits differ from Congo-red-positive or monotypic deposits requiring precise protein typing.

Myeloma cast nephropathy

Abrupt severe AKI with a large light-chain burden and relatively low albumin fraction suggests distal tubular casts rather than glomerular amyloid, although lesions can coexist.

Other nephrotic glomerulopathies

Minimal change disease and FSGS can cause heavy proteinuria without characteristic systemic deposits; electron microscopy, immunofluorescence and Congo-red assessment establish the lesion.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01SuspectRecognise a monoclonal renal syndromeFirst stepAn adult has unexplained proteinuria, CKD, nephrosis or proximal tubular dysfunction.

1Characterise urine albumin and total protein, sediment, renal trajectory and systemic features rather than relying on a dipstick.
2Request serum free light chains plus serum and urine immunofixation and review calcium, blood count and bone symptoms.
3Contact nephrology urgently for rapid functional loss, nephrotic complications or a strong monoclonal signal, adding haematology early when organ injury is likely.

02ProveLink lesion, protein and cloneMonoclonal-protein disease or amyloidosis is plausible.

1Obtain the safest diagnostic tissue through the specialist team, commonly kidney when the renal lesion must be classified.
2Require Congo-red confirmation and accurate amyloid typing or full immunofluorescence/electron-microscopy characterisation of non-amyloid MGRS.
3Complete marrow and systemic staging, reconciling any mismatch through expert renal pathology and the NHS specialised amyloidosis service.

03TreatSuppress the causal precursorTyped amyloid or MGRS has been linked to an actionable clone or inflammatory source.

1Plan clone-directed or precursor-directed therapy in a nephrology–haematology multidisciplinary setting using current disease-specific guidance.
2Adjust regimen and supportive medicines for kidney function, cardiac amyloid, neuropathy, infection risk and volume sensitivity.
3Judge response using both haematological markers and organ measures because a falling light chain does not immediately reverse proteinuria or cardiac dysfunction.

04SupportProtect organs during recoveryThe patient has nephrotic, cardiac, autonomic or CKD complications.

1Manage oedema carefully; cardiac amyloid may tolerate conventional heart-failure medicines and rapid fluid shifts poorly.
2Assess thrombosis, bleeding, infection, hypotension and kidney-replacement needs individually with named specialty ownership.
3Provide genetic or inflammatory-disease referral when non-AL amyloid is typed, avoiding unnecessary chemotherapy for the wrong precursor.

Key medicines and prescribing safety2 treatments · regimens, roles and cautions

Suppresses production of the nephrotoxic monoclonal immunoglobulin or light chain even when the responsible clone is quantitatively small.

Clone-directed therapy for AL amyloid or MGRS

The haematology–nephrology multidisciplinary team must choose and renal-adjust the current disease-specific regimen; no single bortezomib-, antibody- or chemotherapy schedule applies to all lesions.

Cardiac amyloid, autonomic hypotension, neuropathy, cytopenia, infection and renal impairment alter tolerability. Check live NICE access, SmPCs, antiviral or antimicrobial prophylaxis and tumour-lysis planning before treatment.

Relieves salt and water retention while definitive precursor control takes effect.

Loop diuretic for symptomatic oedema

Titrate the locally selected oral or intravenous preparation to congestion, renal response and blood pressure; severe nephrosis or cardiac amyloid often requires specialist-guided adjustment rather than a fixed dose.

Daily weight alone cannot distinguish safe decongestion from intravascular depletion. Monitor orthostasis, creatinine, sodium, potassium and magnesium; combine agents only through an agreed plan, especially with restrictive cardiomyopathy.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Nephrotic complications

Severe albumin loss promotes generalised oedema, venous thrombosis and infection, while autonomic or cardiac amyloid can make fluid removal poorly tolerated.

Progressive kidney failure

Continuing glomerular, tubular or vascular deposition can lead to irreversible chronic kidney disease and a need for kidney replacement therapy.

Cardiac amyloid disease

Myocardial infiltration and restrictive physiology can cause arrhythmia, syncope, heart failure and narrow haemodynamic tolerance, strongly influencing renal and clonal treatment.

Proximal tubular failure

Light-chain proximal tubulopathy may cause phosphate, bicarbonate, glucose, urate and potassium wasting, resulting in acidosis, weakness and defective bone mineralisation.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Trend involved free light chain and the appropriate clonal marker on the haematology schedule, using the same assay where possible.
Follow ACR or PCR, serum albumin, creatinine, eGFR, oedema and diuretic requirement as renal organ-response measures.
Monitor troponin, natriuretic peptide, rhythm and cardiac imaging through the amyloid service when the heart is involved.
Use regimen-specific blood counts, infection surveillance, neuropathy review and renal or hepatic dose checks before each cycle.
Reassess thrombosis and bleeding risks as nephrosis, mobility, platelet count and anticoagulant interactions change.
Plan kidney replacement early when recovery is uncertain; treatment of the clone can remain relevant after dialysis starts.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

MGRS is defined by damage

The kidney lesion creates treatment significance even when the clone would otherwise be labelled MGUS.

Amyloid must be typed

Congo red establishes fibrils, not their precursor; treating hereditary or AA amyloid as AL can cause serious harm.

Protein tests are complementary

Serum free light chains and serum plus urine immunofixation outperform electrophoresis used alone.

Cardiac disease changes renal care

Restrictive physiology and autonomic dysfunction make fluid management and chemotherapy tolerance unusually narrow.

Organ response is delayed

A rapid clonal response is encouraging, but deposited material and structural injury resolve slowly or incompletely.

11Common pitfallsFrequent interpretation and management errors.

01
Dismissing a small paraprotein as MGUS before renal pathology has been explained.
02
Calling Congo-red-positive tissue AL amyloid without definitive protein typing.
03
Using normal serum electrophoresis to exclude a light-chain disorder.
04
Interpreting free-light-chain concentrations without allowing for impaired renal clearance.
05
Giving aggressive diuresis to a patient with amyloid autonomic hypotension and restrictive cardiac filling.
06
Applying a myeloma chemotherapy regimen without lesion-specific multidisciplinary agreement and renal adjustment.