[Bone marrow serous degeneration complicating acute leukemia]

Serous degeneration of bone marrow is a rare hematological complication, of multiple etiologies, which physiopathology is yet to be fully understood. It is described as a focal hypoplasia of the bone marrow and atrophy of its adipocytes coupled with an extracellular deposit of an eosinophilic substance that corresponds to "hyaluronic acid". The prognosis of these lesions depends on the etiological diagnosis.

We report the case of a 19-year-old female patient without no notable pathological history, hospitalized in a regional hospital for mucocutaneous pallor with an impaired general condition. The biological assessment revealed a pancytopenia, and the presence of 60 % blast cells on the blood smear, which was in favor of acute leukemia. As part of the etiological assessment, a bone marrow biopsy was performed, revealing a typical aspect of serous degeneration. The bone marrow cellularity was reduced, made of rare hematopoietic cells, dissociated by pale extracellular deposits that were colored by PAS and alcian blue, with no individualized blasts.

Serous transformation of the hematopoietic marrow is a rare condition, described at the end of the 19th century. The most severe forms are observed in young patients with hypoplasia. It most often manifests as pancytopenia at the beginning, if not then by an isolated cytopenia, anemia or thrombocytopenia. It is interesting to underline the contribution of MRI in diagnosis. The foci of bone marrow serous degeneration are characterized in the long bones by a fluid signal with a T1 hypo-signal and a T2 hyper-signal with no enhancement after injection of gadolinium, unlike bone metastases. The histology of bone marrow biopsy finds focal marrow hypoplasia of the hematopoietic lines associated with a depletion of adipocytes and an eosinophilic gelatinous interstitial infiltration alcian blue and PAS positive. The histological differential diagnosis is amyloidosis due to red Congo positivity, a previous biopsy (the absence of adipose tissue or hematopoietic tissue with granulation tissue and bone formation) and interstitial edema. Bone marrow necrosis can also be observed. Serous degeneration of bone marrow can be a symptom of a chronic systemic illness. In most cases, it is found in cases of severe chronic malnutrition, such as anorexia nervosa, certain cancers (acute leukemia), systemic diseases (lupus) or severe infection. Though there is no specific treatment for this complication, the treatment of the cause most often allows for the complete regression of the peripheral and spinal anomalies.

In rare cases, as is the case in our observation, the serous degeneration of bone marrow can reveal underlying solid tumors or hemopathies, knowledge of it can help guide the investigations towards these etiologies.