Introduction: Amyloidosis AL is a challenging hematological disorder characterized by the extracellular deposition of misfolded monoclonal light chains. Timely and accurate diagnosis is crucial for appropriate management and prognosis. A large portion of patients has a history of monoclonal gammopathy of undetermined significance (MGUS) and therefore bone marrow biopsy (BMB) is generally the most used and best evaluated technique for diagnosing Amyloidosis AL. Other techniques like abdominal fat pad biopsy and skin biopsy are valid and common alternatives. Minor salivary gland biopsy (MSGB) has emerged as a less invasive alternative, offering a promising diagnostic approach but its application is often considered a second option. In this study, we aimed to evaluate the usefulness of MSGB compared to BMB for the diagnosis of amyloidosis AL.
Methods: We conducted a retrospective analysis of 85 patients who underwent both MSGB and BMB for suspected amyloidosis AL from January 2009 to April 2023. All biopsies were evaluated using Congo red staining and immunohistochemistry for amyloid typing. Clinical data, including demographic information, laboratory results, histological characteristics and diagnostic outcomes, were collected. All patients had a monoclonal gammopathy with a clinical or serological suspect for Amyloidosis AL.
Results: Of the 85 patients included in the study, 32 were diagnosed with amyloidosis AL. Among these 32 patients, 21 had positive MSGB and 14 had positive BMB, resulting in a sensitivity of 65.5% (95% CI 46.81% to 81.43%) and 43.75% (95% CI 26.36% to 62.34%) respectively. Concomitant positivity was present in 8 cases. Of the 64 patients with negative MSGB, 53 were not diagnosed with Amyloidosis AL, resulting in a specificity of 99.5% (95% CI: 93.28% to 99.9%). 4 patients with negative MSGB but positive BMB received diagnosis of Amyloidosis AL. 7 patients were diagnosed with Amyloidosis AL despite both negative MSGB and BMB. Of the 53 patients without Amyloidosis AL, 25 received diagnosis of Smouldering Myeloma, 14 of Multiple Myeloma, 4 of Waldenstrom Macroglobulinemia and 10 of MGUS.
Conclusions: To our knowledge, this is one of the largest studies comparing salivary gland and bone marrow biopsies as diagnostic tools in Amyloidosis AL. Our findings demonstrate that minor salivary gland biopsy is a valuable and reliable option with a sensitivity non inferior to other alternatives and, in our case, higher than bone marrow biopsy, thus providing valuable diagnostic information when positive. Comparing our results with data from studies evaluating different bioptic methods for Amyloidosis AL, MSGB holds promise as an initial diagnostic approach, potentially sparing patients from the risks associated with more invasive procedures. Further studies with larger sample sizes and prospective designs are warranted to validate our results and establish standardized protocols for minor salivary gland biopsy as frontrunner in the diagnosis of Amyloidosis AL.
