What is the diagnostic approach for suspected amyloidosis in a patient presenting with unexplained heart failure with ventricular wall thickening, nephrotic‑range proteinuria, peripheral neuropathy, gastrointestinal dysmotility, macroglossia, and a family history or known plasma‑cell dyscrasia?

How to Diagnose Amyloidosis

The diagnosis of amyloidosis requires tissue biopsy demonstrating Congo red-positive deposits with apple-green birefringence under polarized light, followed by mass spectrometry-based typing to identify the precursor protein (AL vs ATTR), combined with comprehensive monoclonal protein screening and systematic organ assessment. 1

Clinical Red Flags That Should Trigger Workup

Suspect amyloidosis when patients present with any combination of the following:

• Cardiac: Unexplained heart failure with preserved ejection fraction (particularly in men), restrictive cardiomyopathy, increased left ventricular wall thickness >12 mm without alternative cause, low QRS voltage on ECG despite ventricular wall thickening 1, 2
• Renal: Unexplained nephrotic-range proteinuria (>3.5 g/day) 1, 3
• Neurologic: Peripheral neuropathy with autonomic features (orthostatic hypotension, gastroparesis), bilateral carpal tunnel syndrome 1, 2
• Gastrointestinal: Macroglossia (highly specific but insensitive), unexplained hepatomegaly with mildly elevated alkaline phosphatase, gastrointestinal dysmotility 1, 4
• Hematologic: Monoclonal gammopathy or multiple myeloma with atypical features, periorbital ecchymoses ("raccoon eyes"), acquired factor X deficiency with coagulopathy 1
• Musculoskeletal: Unexplained biceps tendon rupture, lumbar spinal stenosis 5, 2

Step 1: Initial Laboratory Screening

All patients with suspected amyloidosis must undergo comprehensive monoclonal protein assessment to distinguish AL from ATTR amyloidosis and identify coexisting plasma cell disorders: 1, 5

• Serum free light chain (sFLC) assay with kappa/lambda ratio
• Serum immunofixation electrophoresis (SIFE)
• Urine immunofixation electrophoresis (UIFE) on 24-hour collection
• Bone marrow biopsy if monoclonal protein detected (demonstrates clonal plasma cells in AL amyloidosis with 69% sensitivity for detecting amyloid deposits) 1

Critical pitfall: Do not rely on serum/urine protein electrophoresis (SPEP/UPEP) alone, as these have lower sensitivity than immunofixation, especially in AL amyloidosis where monoclonal protein levels are typically low. 5

Important caveat: Approximately 5% of patients over age 70 have monoclonal gammopathy of uncertain significance (MGUS), and over 10% of patients with monoclonal gammopathy can have ATTR deposits rather than AL amyloidosis. 1, 5 Therefore, abnormal monoclonal protein screening does not automatically confirm AL amyloidosis—tissue typing is mandatory.

Step 2: Tissue Biopsy Strategy

For Suspected AL Amyloidosis:

Start with less invasive surrogate sites first: 1, 5

1. Abdominal fat pad aspiration (84% sensitivity for AL amyloidosis, but only 15% for wild-type ATTR and 45% for hereditary ATTR) 1, 5
2. Bone marrow biopsy (69% sensitivity for systemic AL amyloidosis) 1, 2

If surrogate site biopsies are negative but clinical suspicion remains high, proceed directly to biopsy of the clinically affected organ (endomyocardial, renal, or nerve biopsy). 1, 5 Endomyocardial biopsy has approximately 100% sensitivity and specificity for detecting cardiac amyloid deposits. 5

For Suspected ATTR Cardiac Amyloidosis:

ATTR cardiac amyloidosis can be diagnosed non-invasively without tissue biopsy when ALL of the following criteria are met: 5, 2

• Grade 2 or 3 myocardial uptake on technetium-99m bone scintigraphy (PYP/DPD/HMDP)
• Absence of monoclonal protein on comprehensive screening (sFLC, SIFE, UIFE)
• Typical cardiac imaging features (LV wall thickness >12 mm, relative apical sparing on strain imaging, grade ≥2 diastolic dysfunction)

Critical exception: If ANY monoclonal protein is detected (even MGUS), endomyocardial biopsy is necessary to definitively distinguish between AL and ATTR cardiac amyloidosis, as both can coexist and bone scintigraphy alone is insufficient. 1, 5 In situations of suspected concomitant AL and ATTR cardiac amyloidosis, cardiac biopsy is the preferred route to definitively establish the cardiac pathology. 1

Additional caveat: Some ATTR variants (p.Phe84Leu, p.Ser97Tyr) may show negative bone scintigraphy, requiring alternative diagnostic approaches. 5

Step 3: Amyloid Typing (Mandatory)

Once amyloid deposits are confirmed by Congo red staining, the precursor protein MUST be identified, as this dictates treatment strategy and prognosis: 5, 2

• Mass spectrometry (LC-MS/MS) is the gold standard with 88% sensitivity and 96% specificity 5, 2
• If LC-MS/MS is not immediately available, transfer pathological samples with positive Congo red staining to an experienced reference laboratory for definitive typing 5
• Immunohistochemistry or immunogold immunoelectron microscopy can be performed in experienced centers but are less reliable than mass spectrometry 1, 5, 2

Critical warning: Misdiagnosing amyloid type can lead to inappropriate treatment and patient harm. 5, 2 Never assume AL amyloidosis based solely on monoclonal protein presence without tissue typing. 5

Step 4: Subtype-Specific Confirmation

For AL Amyloidosis:

Diagnosis requires BOTH: 1, 2

1. Demonstration of tissue amyloid deposits (Congo red positive)
2. Evidence of plasma cell dyscrasia (abnormal sFLC ratio, monoclonal protein on SIFE/UIFE, clonal plasma cells on bone marrow biopsy)

Collaborate with a hematologist to exclude multiple myeloma or B-cell lymphoproliferative disorders and guide treatment. 1, 5

For ATTR Amyloidosis:

Perform DNA mutational analysis (TTR gene sequencing) to differentiate between: 5

• Wild-type (senile) ATTR amyloidosis (no mutation)
• Hereditary (variant) ATTR amyloidosis (TTR gene mutation present)

A negative genetic test does not exclude amyloidosis—it simply confirms wild-type ATTR rather than hereditary ATTR. 5

Step 5: Comprehensive Organ Assessment

Systematically evaluate all potentially affected organs, as this is critical for determining treatment strategies and prognosis: 5, 2

• Cardiac: Echocardiography (wall thickness, strain imaging, diastolic function), cardiac MRI (late gadolinium enhancement, extracellular volume >0.40), NT-proBNP (>332 ng/L has >99% sensitivity for cardiac involvement in AL), troponin 1, 5, 2
• Renal: Serum creatinine, 24-hour urine protein quantification 5
• Neurologic: Nerve conduction studies, autonomic function testing 5
• Hepatic: Liver function tests (typically mild elevation of alkaline phosphatase with hepatomegaly) 5, 4

Caution with cardiac MRI: Avoid gadolinium-based contrast agents in patients with estimated GFR <30 mL/min/1.73 m² due to risk of nephrogenic systemic fibrosis. 2

Common Diagnostic Pitfalls to Avoid

• Do not use fat pad biopsy as the sole diagnostic test for suspected ATTR cardiac amyloidosis due to its poor sensitivity (15% for wild-type ATTR). 5, 2
• Do not assume AL amyloidosis in patients with monoclonal gammopathy without proper tissue typing, as ATTR and AL can coexist. 1, 5
• Do not rely on clinical features alone without histological confirmation, as this can lead to misdiagnosis. 2
• In patients with kidney dysfunction, abnormal free light chain ratios may be spurious due to disproportionate urinary loss of lambda light chains; in these cases, immunofixation electrophoresis does not demonstrate a monoclonal protein. 1