To the Editor,
Amyloidosis encompasses several disorders characterized by tissue deposition of misfolded proteins, which lead to multiorgan damage. Diagnosis requires tissue biopsy for accurate amyloid typing, which is essential because treatment strategies differ substantially according to the precursor protein involved. However, the coexistence of monoclonal gammopathies and amyloidosis may create diagnostic uncertainty, particularly when conventional typing techniques yield inconclusive results or when clinical and pathological findings appear discordant [ 1 , 2 ].
Proteomic amyloid typing by mass spectrometry (MS) is increasingly considered the reference standard for amyloid classification because of its high sensitivity and specificity, especially when compared to conventional techniques such as immunofluorescence (IF) and immunohistochemistry (IHC) [ 3 , 4 ].
We describe five diagnostically challenging patients in whom MS established or revised amyloid subtype despite misleading or inconclusive conventional studies, directly influencing clinical management (Table 1 ). For these tissue biopsies, a non-laser microdissection approach was used, followed by proteomic analysis with ultra-high-performance liquid chromatography coupled with high-resolution MS [ 5 ].
Table 1:
Amyloid MS cases
AKI, acute kidney injury; ATTR, transthyretin amyloidosis; BDR, bortezomib, rituximab, dexamethasone; CKD, chronic kidney disease; Dara-VCD, daratumumab, bortezomib, cyclophosphamide, dexamethasone; Dara-VRD, daratumumab, bortezomib, lenalidomide, dexamethasone; uACR, urinary albumin-creatinine ratio; uPCR, urinary protein-creatinine ratio.
| Patient 1 | Patient 2 | Patient 3 | Patient 4 | Patient 5 | |
| Age (years) | 78 | 86 | 61 | 68 | 78 |
| Sex | Female | Female | Male | Male | Male |
| Presentation | Nephrotic syndrome | Nephrotic syndrome | Peripheral neuropathy and cardiac involvement | CKD and subnephrotic proteinuria | Severe AKI requiring hemodialysis |
| Serum creatinine (mg/dl) | 1.88 | 2.48 | 1.05 | 1.65 | 11.5 |
| uACR (mg/g) | 3597 | 7400 | 3.7 | 1168 | Unmeasurable |
| uPCR (mg/g) | 4082 | 9927 | 40.5 | 2101 | Unmeasurable |
| Monoclonal protein | None detected | IgM λ | None detected | IgG λ | IgA κ |
| Bone marrow plasma cells (%) | 2.4 | Patient refused | Not performed | 11 | 26.4 |
| Initial diagnosis | AA amyloidosis | Monoclonal gammopathy | ATTR amyloidosis | Indolent myeloma | IgA κ multiple myeloma |
| Tissue biopsy | Kidney | Kidney | Salivary gland | Kidney | Abdominal fat |
| Congo red | Positive | Positive | Positive | Positive | Positive |
| Conventional typing | AA on IHC | No light-chain restriction | Negative IF/IHC | Negative IF/IHC | No light-chain restriction |
| MS amyloid subtype | AL λ | AL λ | AL λ | AL λ | AL λ |
| Discordance identified | AA vs AL | MGUS without restriction | ATTR vs AL | Indolent myeloma vs AL | κ clone vs λ amyloid |
| Initial management | No hematologic treatment | Watchful waiting | Planned tafamidis | Watchful waiting | Supportive care |
| Post-MS management | Dara-VCD | BDR | Hematologic reassessment | Dara-VRD | No treatment initiated |
| Impact of MS on management | Change in therapy | Treatment initiation | Diagnostic reassessment | Initiation of clone-directed therapy | Diagnostic reclassification |
Patient 1: a 78-year-old woman presenting with nephrotic syndrome was initially diagnosed with AA amyloidosis on kidney biopsy. In the absence of an underlying inflammatory disorder, MS was performed and identified AL λ amyloidosis, resulting in treatment modification.
Patient 2: an 86-year-old woman with nephrotic syndrome and an IgM λ monoclonal gammopathy had amyloid deposits without light-chain restriction on conventional tests. MS confirmed AL λ amyloidosis and supported the decision to initiate treatment.
Patient 3: a 61-year-old man with peripheral neuropathy, cardiac involvement, positive family history, and pathogenic testing for transthyretin amyloidosis, underwent salivary gland biopsy demonstrating amyloid deposits. Despite a clinical picture strongly suggestive of ATTR amyloidosis, MS identified AL λ amyloidosis, raising the possibility of concomitant ATTR and AL λ amyloidosis, prompting hematologic reassessment. Considering the significant prevalence of ATTR hereditary amyloidosis in Portugal along with positive genetic testing and clinical presentation, tafamidis was initiated, maintaining a close surveillance of treatment response and plasma cell dyscrasia.
Patient 4: a 68-year-old man with chronic kidney disease, proteinuria, and an IgG λ monoclonal gammopathy was initially managed with a watchful waiting strategy, as bone marrow biopsy showed 11% plasma cells without myeloma-defining events. Kidney biopsy demonstrated Congo red–positive amyloid deposits with negative IF and IHC, even after pronase digestion. After MS, AL λ amyloidosis diagnosis was established, which led to treatment initiation.
Patient 5: a 78-year-old man with IgA κ multiple myeloma and severe acute kidney injury requiring dialysis had amyloid deposits identified on abdominal fat biopsy. MS demonstrated AL λ amyloid, highlighting discordance between the detected plasma cell clone and the amyloid subtype. Several mechanisms may explain this clone–subtype discordance, including amyloid fibril formation by a quantitatively minor but structurally unstable light chain, lower specificity of conventional techniques in detecting truncated immunoglobulins or biclonal expression [ 6 ]. Owing to rapid clinical deterioration, treatment was not initiated.
In all cases, MS either established or revised the amyloid subtype when conventional tests were inconclusive or inconsistent with the clinical presentation. Notably, the presence of a monoclonal gammopathy did not reliably predict amyloid subtype in three patients, and one patient with genetically confirmed ATTR amyloidosis was ultimately found to have concomitant AL λ amyloidosis. These findings illustrate the limitations of relying solely on conventional typing techniques or monoclonal protein characterization in patients with suspected amyloidosis [ 1 , 2 , 7 ].
The coexistence of monoclonal gammopathy and non-AL amyloidosis represents a well-recognized diagnostic challenge, particularly in older patients. Conversely, the identification of a monoclonal protein may lead clinicians to incorrectly assume AL amyloidosis in the absence of definitive typing. Our cases demonstrate that clinicopathological discordance should prompt further investigation, as both conventional typing techniques and plasma cell clone characterization may fail to accurately identify the amyloid precursor protein.
As access to proteomic amyloid typing expands, MS may play an increasingly important role in resolving diagnostic uncertainty and assist in guiding appropriate subtype-directed therapy [ 3 , 4 ].
ACKNOWLEDGEMENTS
The authors would like to acknowledge the collaboration between the Nephrology, Pathology, and Structural Chemistry teams involved in the diagnostic evaluation of these patients. Generative artificial intelligence tools (ChatGPT, OpenAI GPT-5.5, Claude) were used exclusively for language editing, stylistic refinement, and manuscript organization. All scientific content, clinical interpretation, and final manuscript revision were performed and approved by the authors.
Contributor Information
Manuel Lopes da Silva, Department of Nephrology and Renal Transplantation, Unidade Local de Saúde Santa Maria, Lisbon, Portugal; Faculdade de Medicina da Universidade de Lisboa, Lisbon, Portugal.
Telma Pais, Department of Nephrology and Renal Transplantation, Unidade Local de Saúde Santa Maria, Lisbon, Portugal; Faculdade de Medicina da Universidade de Lisboa, Lisbon, Portugal.
João Boavida, Faculdade de Medicina da Universidade de Lisboa, Lisbon, Portugal; Department of Pathological Anatomy, Unidade Local de Saúde Santa Maria, Lisbon, Portugal.
Carolina Branco, Department of Nephrology and Renal Transplantation, Unidade Local de Saúde Santa Maria, Lisbon, Portugal; Faculdade de Medicina da Universidade de Lisboa, Lisbon, Portugal.
Pedro Pinheiro, Centro de Química Estrutural – Institute of Molecular Sciences, Instituto Superior Técnico, Universidade de Lisboa, Lisbon, Portugal; Departamento de Engenharia Química, Instituto Superior Técnico, Universidade de Lisboa, Lisbon, Portugal; Escola Superior de Tecnologia do Barreiro, Instituto Politécnico de Setúbal, Lavradio, Portugal.
Gonçalo Justino, Centro de Química Estrutural – Institute of Molecular Sciences, Instituto Superior Técnico, Universidade de Lisboa, Lisbon, Portugal; Escola Superior de Tecnologia do Barreiro, Instituto Politécnico de Setúbal, Lavradio, Portugal.
José António Lopes, Department of Nephrology and Renal Transplantation, Unidade Local de Saúde Santa Maria, Lisbon, Portugal; Faculdade de Medicina da Universidade de Lisboa, Lisbon, Portugal.
Natacha Rodrigues, Department of Nephrology and Renal Transplantation, Unidade Local de Saúde Santa Maria, Lisbon, Portugal; Faculdade de Medicina da Universidade de Lisboa, Lisbon, Portugal.
CONFLICT OF INTEREST STATEMENT
None declared.
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