Clinical impact of lilac-colored aggregates on may-Grünwald-Giemsa-stained bone marrow smears in patients with amyloid light-chain amyloidosis

BACKGROUND: Lilac-colored aggregates (LicAGs) are often observed on bone marrow (BM) aspirate smears stained with May-Grünwald-Giemsa (MG) in patients with amyloid light-chain (AL) amyloidosis. However, the clinicopathological features of LicAGs observed on MG-stained BM smears remain poorly understood. METHODS: We examined MG-stained BM aspirate smears and clinical data from 103 patients with AL amyloidosis. To determine whether LicAGs represented amyloid, LicAG-positive specimens were decolorized, re-stained with Congo red, and examined under polarized light. Patients were grouped based on the presence or absence of LicAGs, and their clinical characteristics were compared. Serial changes in LicAG counts following therapy were assessed in two cases. RESULTS: Of the 103 patients, 20 showed LicAGs (BM[+] group), confirmed as amyloid fibrils using Congo red staining. Compared to the BM(-) group, the BM(+) group had higher proportions of κ-type amyloid, liver and tongue involvement, and negative monoclonal immunoglobulin on immunofixation electrophoresis. LicAG counts decreased on serial BM examinations in two patients after treatment. CONCLUSIONS: LicAGs are amyloid fibrils, indicating their potential significance in AL amyloidosis, especially when monoclonal immunoglobulins are undetectable. They may also serve as indicators of organ involvement and as surrogate markers for treatment response.