How to rule out amyloidosis?

Diagnostic Approach to Rule Out Amyloidosis

To definitively rule out amyloidosis, tissue biopsy with Congo red staining and mass spectrometry-based typing is required, with the specific approach depending on suspected amyloid type and clinical presentation. 1

Clinical Suspicion: When to Consider Amyloidosis

Amyloidosis should be suspected in patients presenting with:

• Cardiac manifestations:

  • Restrictive cardiomyopathy
  • Heart failure with preserved ejection fraction (HFpEF)
  • Left ventricular wall thickness ≥14mm with fatigue, dyspnea, or edema
  • Arrhythmias, especially atrial fibrillation 2

• Extracardiac manifestations:

  • Unexplained proteinuria
  • Macroglossia (highly specific for AL amyloidosis)
  • Periorbital ecchymoses (highly specific for AL amyloidosis)
  • Peripheral neuropathy with autonomic features
  • Bilateral carpal tunnel syndrome
  • Hepatomegaly with elevated alkaline phosphatase
  • Acquired factor X deficiency with coagulopathy 1, 3
  • Gastrointestinal symptoms (malabsorption, bloating, nausea, diarrhea) 4

Diagnostic Algorithm

Step 1: Initial Screening Tests

• Serum and urine monoclonal protein studies:

  • Serum free light chain assay
  • Serum protein electrophoresis (SPEP)
  • Serum immunofixation electrophoresis (IFE)
  • Urine protein electrophoresis (UPEP)
  • Urine immunofixation electrophoresis 1, 2

• Cardiac biomarkers (if cardiac involvement suspected):

  • BNP/NT-proBNP (sensitivity 93%, specificity 90%)
  • Troponin 2

Step 2: Tissue Diagnosis

The gold standard for diagnosis is tissue biopsy with Congo red staining, which appears red in normal light and apple-green under polarized light 1, 5.

For AL amyloidosis suspicion:

1. Biopsy approach options:

   • Option A: Start with surrogate site biopsy:

     • Abdominal fat aspiration (sensitivity: 84% for AL-CM)
     • Bone marrow biopsy (sensitivity: 69% for systemic AL)
     • If negative, proceed to affected organ biopsy

   • Option B: Direct biopsy of the affected organ 1

For ATTR amyloidosis suspicion:

• Nuclear scintigraphy (Tc-PYP scan) can diagnose ATTR cardiac amyloidosis without biopsy if monoclonal protein studies are negative 1

Step 3: Amyloid Typing

If Congo red staining is positive, determine the precursor protein:

1. Mass spectrometry analysis (LC-MS/MS): Gold standard (sensitivity 88%, specificity 96%)
2. Alternative typing methods (if LC-MS/MS unavailable):
   • Immunohistochemistry
   • Immunogold immunoelectron microscopy
   • Immunofluorescence 1, 6, 5

Step 4: Exclude Related Disorders

• For AL amyloidosis: Exclude multiple myeloma or B-cell lymphoproliferative disorders
• For ATTR amyloidosis: Genetic testing to distinguish between wild-type and hereditary forms 1, 2

Important Considerations and Pitfalls

• Monoclonal protein interpretation: Abnormal monoclonal protein may indicate:

  • AL amyloidosis
  • Multiple myeloma
  • Monoclonal gammopathy of uncertain significance (MGUS)
  • Spurious result due to kidney dysfunction 1

• Diagnostic challenges:

  • MGUS prevalence increases with age (affects ~5% of patients >70 years)
  • Patients with ATTR-CM may have concomitant MGUS
  • In kidney dysfunction, disproportionate urinary loss of lambda light chains may occur 1

• Concomitant amyloidosis: In situations of suspected concomitant AL and ATTR cardiac amyloidosis (such as MGUS with abnormal nuclear scintigraphy), cardiac biopsy is preferred to definitively establish cardiac pathology 1

• Hematology consultation: When monoclonal protein testing is abnormal, collaborate with a hematologist to determine whether findings represent kidney dysfunction, MGUS, AL amyloidosis, or multiple myeloma 1

• Sample handling: Pathological samples with positive Congo red staining can be transferred to specialized reference laboratories for LC-MS/MS if not locally available 1, 6

By following this structured approach, clinicians can effectively rule out amyloidosis or establish the specific type, which is crucial for determining appropriate treatment strategies and improving patient outcomes.