Importance of quantitative histology of bone changes in monoclonal gammopathy

Quantitative histology of bone changes, using undecalcified transiliac bone biopsies (UTBB), was performed blindly in 46 individuals with monoclonal gammopathy (MG), including 17 with MG of undetermined significance (MGUS) and 29 with overt multiple myeloma (MM). Three MGUS presented an excess of osteoclastic resorption (OR) in the vicinity of clusters of tumour cells and developed overt B cell malignancies, chronic lymphocytic leukaemia, Waldenström's disease and MM respectively. On the other hand, MGUS with normal OR remained stable (median follow-up = 28 months), with one exception who developed a systemic amyloidosis. In MM, excessive OR was only observed in areas invaded by myeloma cells. OR was frequently normal in active MM lacking myeloma cells in UTBB. Active MM without lesions on radiography had excessive OR. IgA and pure Bence Jones MM appeared more osteoclastic than IgG cases (P less than 0.05). Of major interest was the finding that one third of MM presented histological bone changes similar to osteoporosis, osteosclerosis or osteoblastic metastasis. Two major findings must be emphasized from the current data: UTBB could be of major interest for the early detection of a B cell malignancy; heterogeneity of myeloma bone condition is unexpected. If some changes appear directly related to the tumour (i.e. excessive OR or osteoblastic dysfunction), some others are probably accidentally associated with it (i.e. osteoporosis), both needing treatment other than chemotherapy.