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We recently published a study aiming to verify the frequency of amyloid deposits in the bone marrow of patients with multiple myeloma (MM) who did not present any signs or symptoms of systemic amyloidosis, applying the Congo red technique on bone marrow smears obtained by aspiration from the posterior iliac spine. The results suggested that nearly 40% of patients affected by MM may have amyloid deposits in their bone marrow. Subsequently, this finding has not been confirmed by another study performed with histological specimens of bone marrow in a similar clinical setting. To explain this discrepancy, we performed a comparative study on the bone marrows of 36 patients affected by MM, evaluated by both cytological and histological techniques. The results of this study confirm the high frequency of amyloid deposits in the bone marrow of patients affected by MM when the analysis is made on cytological smears, and indicate that the presence of amyloid on marrow smears is confirmed by core biopsies simultaneously performed in only 25% of cases. Should further studies confirm our findings, cytological assessment could be considered a sensitive technique to detect bone marrow amyloid deposits.

Systemic AL amyloidosis is associated with nearly 15% of cases of multiple myeloma, but data on the frequency and significance of amyloid deposits in the bone marrow of patients affected by multiple myeloma without clinical signs of systemic amyloidosis are scanty. Bone marrow smears of 166 unselected patients affected by multiple myeloma (126 at diagnosis and 40 after treatment) were stained with Congo red and studied by transmission and birefringence microscopy. Both focal and diffuse storages were considered positive. Overall, 67 patients were positive and 99 were negative to Congo red and apple-green birefringence. In particular, 51 of the 126 patients studied at diagnosis and 16 of the 40 patients with advanced disease were positive. Seventeen patients were reassessed after a mean follow-up of 32 months (range: 6-91): disappearance of amyloid deposits was verified in three cases, all responsive to bortezomib-based regimens. The preliminary data available suggest that amyloid deposition in the marrow of myeloma patients is frequent, as it can be traced in nearly 40% of cases. We failed to find correlations between bone marrow amyloid deposits and immunoglobulin type, disease stage, plasma cells percentage, hemoglobin, calcium, creatinine, albumin, or beta(2)microglobulin. Significantly higher incidence of moderate/severe peripheral neuropathy was found in patients with marrow amyloid exposed to potentially neurotoxic antineoplastic agents. Further studies and prolonged follow-up are needed to validate our findings and to define possible prognostic aspects.