What is the appropriate diagnostic work‑up for a patient with suspected amyloidosis?

Diagnostic Work-Up for Suspected Amyloidosis

The diagnostic work-up for suspected amyloidosis requires simultaneous comprehensive monoclonal protein screening (serum free light chains, serum and urine immunofixation), followed by tissue biopsy with Congo red staining and mass spectrometry-based amyloid typing, combined with systematic organ assessment—with the specific pathway diverging based on whether monoclonal protein is detected. 1, 2

Step 1: Comprehensive Monoclonal Protein Screening (Mandatory First Step)

• Order all three tests simultaneously within the first clinical encounter: serum free light chain (sFLC) assay with κ/λ ratio, serum immunofixation electrophoresis (SIFE), and urine immunofixation electrophoresis (UIFE). 2, 3

• This triple-test combination achieves >99% sensitivity for detecting AL amyloidosis and is essential because approximately 5% of individuals over 70 years have monoclonal gammopathy of undetermined significance (MGUS), and >10% of patients with a monoclonal protein actually harbor ATTR rather than AL deposits. 2

• Delays beyond 6 weeks in obtaining monoclonal protein screening are associated with increased early mortality, making this an urgent priority. 3, 4

• Normal sFLC κ/λ ratio is 0.26–1.65 (Binding Site assay) or 0.31–1.56 (Siemens assay); in renal dysfunction the upper limit may widen to 3.7, requiring cautious interpretation. 2

• 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. 2

Step 2: Initial Cardiac and Laboratory Assessment

Cardiac Biomarkers

• Measure NT-proBNP (or BNP if unavailable), which is disproportionately elevated relative to the degree of heart failure with 93% sensitivity and 90% specificity for cardiac involvement; NT-proBNP ≥332 ng/L provides >99% sensitivity for cardiac involvement in AL amyloidosis. 2, 3

• Measure cardiac troponin (T, I, or high-sensitivity), which is often markedly elevated beyond what the clinical picture would predict. 1, 3

Electrocardiography

• Obtain a 12-lead ECG to assess for voltage-mass discordance (low QRS voltage <0.5 mV in limb leads despite increased wall thickness on imaging) and pseudoinfarct pattern (Q waves unrelated to prior myocardial infarction). 1, 3

• Low voltage is present in approximately 50% of AL amyloidosis cases but only 25% of ATTR cases, limiting its sensitivity as a screening test. 1

Transthoracic Echocardiography (Mandatory)

• Perform echocardiography in all patients with suspected amyloidosis to assess for left ventricular wall thickness ≥12 mm without alternative cause (hypertension, aortic stenosis), biatrial enlargement, restrictive transmitral Doppler filling pattern, and thickened valves. 1, 2

• Evaluate for apical-sparing pattern on longitudinal strain imaging (apical-to-basal strain ratio >2.1), which is highly specific for cardiac amyloidosis. 1, 2, 4

• Look for granular "sparkling" myocardial appearance, pericardial effusion, and right ventricular wall thickening. 1

Additional Laboratory Tests

• Complete blood count with differential, serum creatinine with estimated glomerular filtration rate (eGFR), serum albumin, alkaline phosphatase (hepatomegaly with elevated alkaline phosphatase suggests hepatic involvement), and urinalysis with 24-hour urine protein quantification. 2, 3

Step 3: Divergent Pathways Based on Monoclonal Protein Results

Pathway A: Monoclonal Protein DETECTED (Suspect AL Amyloidosis)

Tissue Biopsy Strategy

• Abdominal fat pad aspiration is the first-line biopsy site, with 84% sensitivity for AL cardiac amyloidosis but only 15% sensitivity for wild-type ATTR and 45% for hereditary ATTR. 2, 3, 4

• Bone marrow biopsy (69% sensitivity for systemic AL) should be performed to demonstrate clonal λ or κ-producing plasma cells and exclude multiple myeloma or B-cell lymphoproliferative disorders. 1, 2, 3

• If fat pad and bone marrow biopsies are negative but clinical suspicion remains high, proceed directly to biopsy of the clinically affected organ (endomyocardial, renal, or nerve biopsy). 2

Amyloid Typing (Mandatory)

• Mass spectrometry (LC-MS/MS) of the biopsy specimen is the gold standard for amyloid typing, with 88% sensitivity and 96% specificity. 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. 2

• Immunohistochemistry or immunogold immunoelectron microscopy can be performed in experienced centers but are less reliable than mass spectrometry. 2, 5

Hematology Collaboration

• Refer to a hematologist for evaluation of the underlying plasma cell disorder and to guide chemotherapy or immunotherapy targeting the aberrant plasma cells. 2

Pathway B: Monoclonal Protein ABSENT (Suspect ATTR Amyloidosis)

Nuclear Imaging (Non-Invasive Diagnosis)

• Proceed directly to technetium-99m bone scintigraphy (⁹⁹ᵐTc-PYP in the USA; ⁹⁹ᵐTc-DPD or ⁹⁹ᵐTc-HMDP elsewhere) with SPECT imaging. 1, 2

• Non-invasive ATTR cardiac amyloidosis diagnosis is confirmed when ALL of the following criteria are met:

  1. Visual myocardial uptake grade 2 or 3 (grade 2 = uptake equal to bone; grade 3 = uptake greater than bone)
  2. Heart-to-contralateral lung ratio >1.5 at 1 hour (or >1.3 at 3 hours)
  3. SPECT confirmation of true myocardial retention (excludes blood-pool or rib activity)
  4. Absence of monoclonal protein on comprehensive screening
  5. Typical cardiac imaging features (LV wall thickness >12 mm, apical-sparing strain pattern, grade ≥2 diastolic dysfunction) 1, 2

• Always perform SPECT imaging after planar bone scintigraphy; planar images alone may produce false-positive uptake from blood-pool or rib activity. 2

Genetic Testing

• TTR gene sequencing is mandatory once ATTR amyloidosis is established to differentiate wild-type (senile) from hereditary (variant) ATTR, guide family screening, and determine eligibility for genotype-specific therapies. 1, 2

• A negative genetic test confirms wild-type ATTR rather than hereditary ATTR but does not exclude amyloidosis altogether. 2

Pathway C: Monoclonal Protein PRESENT (Including MGUS) with Positive Bone Scintigraphy

• Endomyocardial biopsy with mass spectrometry typing is mandatory because bone scintigraphy cannot reliably differentiate AL from ATTR when any monoclonal protein is detected; up to 40% of patients with ATTR cardiac amyloidosis have coexisting MGUS, and >10% of patients with grade 2–3 PYP uptake still have AL amyloidosis. 1, 2

• Endomyocardial biopsy has approximately 100% specificity and sensitivity for detecting cardiac amyloid deposits. 1

Step 4: Cardiac Magnetic Resonance (Complementary, Not Primary)

• Cardiac MRI should be reserved for cases where echocardiography shows suggestive but not definitive findings, when additional tissue characterization is required, or to confirm suspected apical hypertrophy or aneurysm. 2, 3

• Typical CMR findings include diffuse subendocardial or transmural late gadolinium enhancement (LGE), global extracellular volume (ECV) >0.40, elevated native T1 values (>1020–1044 ms), and abnormal gadolinium kinetics with myocardial nulling preceding blood-pool nulling. 1, 2, 3

• CMR cannot reliably differentiate ATTR from AL amyloidosis, reinforcing its role as a complementary modality rather than a definitive sub-typing tool. 2

• Gadolinium-based contrast agents must be avoided when eGFR <30 mL/min/1.73 m² due to the risk of nephrogenic systemic fibrosis. 2

Step 5: Systematic Organ Assessment

• Systematically evaluate all potentially affected organs, as this is critical for determining treatment strategies and prognosis. 1, 2

Renal Assessment

• Measure serum creatinine, eGFR, and 24-hour urine protein; nephrotic-range proteinuria (>3.5 g/24 h) is a red flag for renal amyloid involvement. 2

Neurologic Assessment

• Screen for peripheral sensorimotor neuropathy with length-dependent axonal and demyelinating features, and autonomic dysfunction (orthostatic hypotension, erectile dysfunction, abnormal sweating, gastroparesis, chronic diarrhea). 1, 2, 4

Hepatic Assessment

• Hepatomegaly with mildly elevated alkaline phosphatase while other liver function tests remain normal suggests hepatic amyloid deposition. 2, 4

Musculoskeletal Assessment

• Document history of bilateral carpal tunnel syndrome (especially in males without rheumatoid arthritis or occupational trauma), lumbar spinal stenosis requiring surgical intervention, or spontaneous biceps tendon rupture. 1, 4

Critical Pitfalls to Avoid

• Never interpret bone scintigraphy without concurrent monoclonal protein screening; omission can lead to misdiagnosis because the scan alone cannot separate AL from ATTR in the presence of a plasma-cell disorder. 1, 2

• Do not assume AL amyloidosis solely on the basis of a detected monoclonal protein without tissue typing; >10% of patients with monoclonal gammopathy actually have ATTR deposits, and both AL and ATTR can coexist. 2

• Relying on fat pad biopsy alone for suspected ATTR cardiac amyloidosis is inappropriate due to its unacceptably low sensitivity (15% for wild-type ATTR, 45% for hereditary ATTR). 2, 4

• Do not skip endomyocardial biopsy when any monoclonal protein is present, even if bone scintigraphy shows grade 2–3 uptake, as this is the only way to definitively distinguish AL from ATTR cardiac amyloidosis. 1, 2

• Interpret sFLC ratios cautiously in renal dysfunction, as impaired clearance can falsely elevate the κ/λ ratio. 2

• Hypertrophic cardiomyopathy is frequently mistaken for amyloidosis when left ventricular wall thickening is present; careful assessment for voltage-mass discordance helps differentiate the two. 1, 4

• A substantial proportion of cases labeled as undifferentiated heart failure with preserved ejection fraction (HFpEF) are actually undiagnosed amyloidosis; clinicians should consider amyloid screening in this population. 1, 4

Clinical Red Flags That Should Trigger This Work-Up

• Heart failure with preserved ejection fraction (EF ≥40%) in men older than 60 years, especially when symptoms are disproportionately severe. 1, 4

• Left ventricular wall thickness ≥12–14 mm in the absence of hypertension or aortic stenosis. 2, 3, 4

• Intolerance to ACE-inhibitors, ARBs, or β-blockers manifested as symptomatic hypotension. 1, 4

• Hypertension that paradoxically resolves over time as myocardial infiltration progresses. 1, 4

• NT-proBNP levels >3000 pg/mL that are disproportionately high relative to the clinical severity of heart failure. 1, 4

• Low-flow aortic stenosis (mean gradient ≤40 mm Hg) with preserved ejection fraction in patients >60 years. 4

• Bilateral carpal tunnel syndrome in males without rheumatoid arthritis or occupational trauma. 1, 4

• Unexplained peripheral neuropathy with autonomic dysfunction. 1, 2, 4

• Macroglossia or periorbital purpura ("raccoon eyes"), which are highly specific for AL amyloidosis. 2, 4

• Unexplained proteinuria, especially nephrotic-range. 2, 4