What is the recommended diagnostic workup and first‑line treatment for amyloid accumulation, distinguishing AL (light‑chain) amyloidosis, ATTR (transthyretin) amyloidosis, and cerebral β‑amyloid disease?

Diagnostic Workup and First-Line Treatment for Amyloid Accumulation

For AL amyloidosis, first-line treatment is daratumumab with cyclophosphamide, bortezomib, and dexamethasone (Dara-CyBorD), while ATTR amyloidosis requires TTR stabilizers or gene silencers, and cerebral β-amyloid disease diagnosis relies on CSF biomarkers (low Aβ42 or increased Aβ40-Aβ42 ratio) plus phosphorylated tau with corresponding clinical phenotype. 1, 2

AL (Light-Chain) Amyloidosis

Diagnostic Workup

The diagnosis requires both tissue amyloid deposits AND evidence of plasma cell dyscrasia 1:

Step 1: Monoclonal Protein Screening

• Serum free light chains (sFLC) - most critical
• Serum immunofixation electrophoresis (SIFE)
• Urine immunofixation electrophoresis (UIFE)
• Do NOT use SPEP/UPEP alone - insufficient sensitivity for AL amyloidosis 1

Step 2: Tissue Biopsy Strategy

Two approaches 1:

1. Surrogate site first: Abdominal fat aspiration (84% sensitivity for AL-CM) or bone marrow biopsy (69% sensitivity)

   • If negative → proceed to affected organ biopsy

2. Direct affected organ biopsy if high suspicion

Step 3: Amyloid Typing

• Congo red staining to confirm amyloid deposits
• Mass spectrometry (LC-MS/MS) - gold standard for protein typing (88% sensitivity, 96% specificity) 1
• Critical when MGUS coexists with suspected ATTR

Step 4: Bone Marrow Confirmation

• Demonstrate clonal proliferation of lambda or kappa-producing plasma cells
• Exclude multiple myeloma or B-cell lymphoma 1

First-Line Treatment

Dara-CyBorD (daratumumab + cyclophosphamide + bortezomib + dexamethasone) is now the preferred first-line therapy 1:

• This regimen has supplanted high-dose melphalan with autologous stem cell transplantation (HDM/SCT) as standard of care
• HDM/SCT reserved only for highly selected patients at low risk for treatment-related mortality
• No absolute contraindications based on ejection fraction or cardiac status 1

Critical Monitoring During Treatment

Close cardiology collaboration essential for 1:

• Decompensated heart failure
• Atrial arrhythmias
• Thromboembolism
• Specific cardiotoxicities: Daratumumab causes cardiac failure in 12% (grade 3-4 in 6%), cardiac arrhythmia in 8%

ATTR (Transthyretin) Amyloidosis

Diagnostic Workup

Non-invasive diagnosis possible without tissue biopsy in cardiac ATTR 1:

Step 1: Exclude AL Amyloidosis First

• Complete monoclonal protein screen (sFLC, SIFE, UIFE)
• Must be negative before proceeding

Step 2: Technetium-99m Pyrophosphate (Tc-PYP) Scintigraphy

• High tracer retention diagnostic for ATTR-CM when monoclonal protein screen negative
• If positive WITH monoclonal gammopathy → cardiac biopsy required to distinguish AL from ATTR 1

Step 3: Genetic Testing

• TTR gene sequencing to distinguish hereditary (ATTRv) from wild-type (ATTRwt)
• Critical for family counseling and treatment selection

First-Line Treatment

TTR tetramer stabilizers or TTR gene silencers 3:

For Both Polyneuropathy and Cardiomyopathy:

• Tafamidis (stabilizer)
• Vutrisiran (gene silencer - siRNA)

For Polyneuropathy Only:

• Patisiran (gene silencer - siRNA)
• Eplontersen (gene silencer - antisense oligonucleotide)
• Diflunisal (stabilizer)

For Cardiomyopathy Only:

• Acoramidis (stabilizer)

Treatment most effective before significant end-organ dysfunction develops - early diagnosis critical 3

Cerebral β-Amyloid Disease (Alzheimer's Disease)

Diagnostic Workup

Requires specific clinical phenotype PLUS both amyloid AND tau biomarker positivity 2:

Clinical Phenotype Required:

• Amnestic syndrome of hippocampal type (gradual progressive memory impairment)
• Isolated amyloid positivity without tau is NOT specific for Alzheimer's disease

Biomarker Testing (Prioritize CSF):

Amyloid β pathology - one of:

• Low CSF Aβ42
• Increased CSF Aβ40-Aβ42 ratio (preferred)
• High tracer retention on amyloid PET

Tau pathology - one of:

• High CSF phosphorylated tau (NOT total tau - low specificity)
• Increased ligand retention on tau PET

Testing Strategy:

• CSF investigation prioritized - provides simultaneous amyloid and tau information, less expensive than PET 2
• PET alternative if lumbar puncture contraindicated
• Plasma biomarkers NOT currently recommended - require further standardization 2

Treatment

Not addressed in provided evidence (focused on diagnosis)

Critical Pitfalls to Avoid

1. Using SPEP/UPEP alone for AL amyloidosis screening - inadequate sensitivity 1

2. Accepting Congo red staining alone without mass spectrometry typing - over 10% of patients with monoclonal gammopathy have ATTR deposits 1

3. Diagnosing ATTR-CM without excluding monoclonal protein - can miss concomitant AL amyloidosis 1

4. Diagnosing Alzheimer's disease with amyloid positivity alone - requires both amyloid AND tau positivity with appropriate clinical phenotype 2

5. Delaying treatment initiation - outcomes dramatically worse with advanced organ damage in both AL and ATTR amyloidosis 3, 4