Diagnostic Evaluation for Unexplained Multisystem Organ Dysfunction Suspicious for Amyloidosis
When to Suspect Amyloidosis: Clinical Red Flags
In any patient with unexplained multisystem organ dysfunction, amyloidosis should be immediately suspected when two or more of the following red-flag features are present:
Cardiac Red Flags
- Left ventricular wall thickness > 12 mm without hypertension or aortic stenosis 1
- Heart failure with preserved ejection fraction (EF ≥ 40%), especially in men > 60 years 1
- Low QRS voltage on ECG despite increased wall thickness (voltage-mass discordance) 1
- Intolerance to ACE-inhibitors or β-blockers with symptomatic hypotension 1
- Atrial fibrillation with right ventricular wall thickening 1
Renal Red Flags
- Nephrotic-range proteinuria (> 3.5 g/24 hours) without diabetes or other glomerular disease 1, 2
- Unexplained proteinuria in adults > 40 years 3, 4
Neurologic Red Flags
- Bilateral carpal tunnel syndrome, particularly in males without rheumatoid arthritis 1
- Peripheral sensorimotor neuropathy with autonomic dysfunction (orthostatic hypotension, gastroparesis, erectile dysfunction) 1, 2
Other Systemic Red Flags
- Macroglossia 2
- Unexplained hepatomegaly with mildly elevated alkaline phosphatase 1, 3, 4
- Biceps tendon rupture or lumbar spinal stenosis 1
- Periorbital ecchymoses ("raccoon eyes") or acquired factor X deficiency 1
Mandatory Initial Laboratory Screening (Perform Simultaneously)
All three of the following tests must be ordered together in every patient with suspected amyloidosis—this is non-negotiable:
Critical pitfall: Do NOT rely on serum/urine protein electrophoresis (SPEP/UPEP) alone—these have lower sensitivity than immunofixation, especially in AL amyloidosis where monoclonal protein levels are typically low 1. Approximately 5% of individuals > 70 years have monoclonal gammopathy of uncertain significance (MGUS), and > 10% of patients with a monoclonal protein may harbor ATTR rather than AL deposits 1, 2.
Tissue Biopsy Strategy: Two Pathways Based on Clinical Suspicion
Pathway A: Suspected AL Amyloidosis (Monoclonal Protein Present)
Start with less invasive biopsy sites first:
- Abdominal fat pad aspiration (84% sensitivity for AL amyloidosis) 1, 2
- Bone marrow biopsy (69% sensitivity for systemic AL) 1, 2
- Also demonstrates clonal plasma cell population (typically λ light chains in 75–80% of AL cases) 2
If both are negative but clinical suspicion remains high, proceed immediately to biopsy of the clinically affected organ (endomyocardial, renal, or nerve biopsy) 1, 2.
Critical pitfall: Fat pad biopsy has unacceptably low sensitivity for ATTR amyloidosis (only 15% for wild-type ATTR, 45% for hereditary ATTR)—do not use it as the sole diagnostic test when ATTR is suspected 1.
Pathway B: Suspected ATTR Cardiac Amyloidosis (No Monoclonal Protein)
Non-invasive diagnosis is acceptable when ALL of the following criteria are met:
- Grade 2–3 myocardial uptake on technetium-99m bone scintigraphy (PYP in USA, DPD/HMDP elsewhere) 1, 5
- Grade 2 = myocardial uptake equal to bone
- Grade 3 = myocardial uptake greater than bone 1
- Heart-to-contralateral lung ratio > 1.5 at 1 hour (or > 1.3 at 3 hours) 1
- SPECT imaging confirms true myocardial uptake 1
- Absence of any monoclonal protein on comprehensive screening 1
- Typical cardiac imaging features (LV wall thickness > 12 mm, apical-sparing strain pattern, grade ≥ 2 diastolic dysfunction) 1
Critical pitfall: If ANY monoclonal protein is detected (even MGUS), endomyocardial biopsy is mandatory because bone scintigraphy cannot reliably differentiate AL from ATTR when a monoclonal protein is present—> 10% of patients with Grade 2–3 PYP uptake still have AL amyloidosis 1, 2.
Amyloid Typing (Mandatory After Positive Congo Red Staining)
Mass spectrometry (LC-MS/MS) is the gold standard for identifying the amyloid precursor protein (88% sensitivity, 96% specificity) 1, 2. If LC-MS/MS is not immediately available, transfer pathological samples with positive Congo red staining to an experienced reference laboratory 1.
Do NOT rely solely on immunohistochemistry or immunogold immunoelectron microscopy—these are less reliable than mass spectrometry 1, 2.
Subtype-Specific Confirmation
For Confirmed AL Amyloidosis
- Bone marrow biopsy demonstrates clonal plasma cells (> 10% plasma cells suggests multiple myeloma rather than isolated AL) 2
- Immediate hematology referral for evaluation of plasma cell disorder and initiation of chemotherapy or immunotherapy 1, 6
For Confirmed ATTR Amyloidosis
- DNA sequencing of the TTR gene differentiates wild-type (no mutation) from hereditary (mutation-positive) ATTR 1
- A negative genetic test confirms wild-type ATTR, not absence of amyloidosis 1
Comprehensive Organ Assessment (Required in All Patients)
Cardiac Evaluation (Mandatory)
Transthoracic echocardiography assessing:
Cardiac biomarkers:
Cardiac MRI (if eGFR ≥ 30 mL/min/1.73 m²):
Renal Evaluation
- Serum creatinine, eGFR, 24-hour urine protein 1
Neurologic Evaluation
- Screen for peripheral neuropathy and autonomic dysfunction (orthostatic blood pressure measurements) 1
Hepatic Evaluation
- Liver function tests, hepatomegaly assessment 1
Critical Diagnostic Pitfalls to Avoid
Never interpret bone scintigraphy results without concurrent monoclonal protein screening—this is the most common error leading to misdiagnosis 1
Never assume AL amyloidosis based solely on monoclonal protein presence without tissue typing—ATTR and AL can coexist in > 10% of cases 1, 2
Never rely on fat pad biopsy alone for suspected ATTR cardiac amyloidosis due to its 15% sensitivity 1
Never skip immunofixation in favor of SPEP/UPEP alone—immunofixation is far more sensitive 1
In renal dysfunction, sFLC ratios may be falsely elevated—interpret with caution and prioritize immunofixation 1
When both AL and ATTR cardiac amyloidosis are suspected, cardiac biopsy is the preferred definitive approach 1