Amyloid Deposits in Bone Marrow Smears of Multiple Myeloma

Objective: Amyloid deposits (AD) in bone marrow (BM) of multiple myeloma (MM) patients might herald systemic AL amyloidosis. The purpose of this study has been to detect AD in bone marrow smears of MM patients and to compare AD status with clinical and Ig serological status (light and heavy chains).Methods: BM smears of 22 consecutive patients were utilized; twelve were from patients at diagnosis and 10 from patients after effective treatment or relapsed. BM air-dried smears were stained by Congo red and evaluated by transmission birefringence microscopy. AD were identified as diffuse, dense, blob-like amorphous pink material with sharp outlines or focal strips of pink, stroma-like material with bone marrow cells tightly attached. These AD showed apple-green birefringence in both presentations. Plasma cell intracellular reddish spindle-shaped inclusions (Auer rods–like) were also detected in positive cases. Both cytological presentations were considered positive.Results: Eleven cases (50%) were positive for AD: no relations with clinical status (5 patients at the diagnosis and 6 with advanced disease), bone marrow plasma cell percentage or Ig isotype were found. Conclusions: AD may be easily detected on BM smears by Congo red stain and their incidence seems higher than that reported in literature (about 15%). Enlarged cohort and prolonged follow-up are needed to assess their possible prognostic significance.