[Gelatinous transformation of the bone marrow: A retrospective monocentric case series of 12 patients]

Gelatinous transformation of bone marrow: rare or underdiagnosed?

Gelatinous transformation of the bone marrow (GTBM) is a rare hematologic entity, which was first described by Paul Michael in 1930. GTBM is mostly associated with caloric intake/anorexia nervosa, although it also has been described accompanying other pathologic conditions, such as malignancy, systemic lupus erythematosus, HIV infections. Even though the diagnostic features of the hematopoietic tissue, such as hypoplasia, adipose cell atrophy, and deposition of a gelatinous substance in the bone marrow (which stains with Alcian blue at pH 2.5) are quite specific, the underlying pathogenic mechanisms remain poorly understood. Considering the evidence of reversibility—notably in cases of malnutrition and anorexia—this entity should be kept high on cards as a possible differential diagnosis of patients presenting with cytopenias and associated weight loss or starvation, especially in developing countries with nutritionally deprived populations. On an extensive review of the literature aimed at comprehensively addressing the evolution of the GTBM from the past century until now, we conclude that the lack of clinical suspicion and awareness regarding this pathologic entity has led to misdiagnosis and delayed diagnosis.

Increased Bone Marrow Adiposity in a Context of Energy Deficit: The Tip of the Iceberg?

Elevated bone marrow adiposity (BMA) is defined as an increase in the proportion of the bone marrow (BM) cavity volume occupied by adipocytes. This can be caused by an increase in the size and/or number of adipocytes. BMA increases with age in a bone-site-specific manner. This increase may be linked to certain pathophysiological situations. Osteoporosis or compromised bone quality is frequently associated with high BMA. The involvement of BM adipocytes in bone loss may be due to commitment of mesenchymal stem cells to the adipogenic pathway rather than the osteogenic pathway. However, adipocytes may also act on their microenvironment by secreting factors with harmful effects for the bone health. Here, we review evidence that in a context of energy deficit (such as anorexia nervosa (AN) and restriction rodent models) bone alterations can occur in the absence of an increase in BMA. In severe cases, bone alterations are even associated with gelatinous BM transformation. The relationship between BMA and energy deficit and the potential regulators of this adiposity in this context are also discussed. On the basis of clinical studies and preliminary results on animal model, we propose that competition between differentiation into osteoblasts and differentiation into adipocytes might trigger bone loss at least in moderate-to-severe AN and in some calorie restriction models. Finally, some of the main questions resulting from this hypothesis are discussed.