[Course of bone tissue after bone marrow allograft in adolescents with sickle cell disease]

Allogenic B.M.T. has been investigated as a curative treatment of anemia in S.C.D. Furthermore, correction of functional asplenia has been observed after B.M.T.; it remains to be determined if such a treatment may reserve other organ damage and particularly bone abnormalities and osteonecrosis frequently associated with S.C. hemoglobinopathies.

The aim of this retrospective review was to evaluate the radiologic and MRI results of 2 patients with avascular necrosis before the B.M.T. Roentgenographic diagnosis of osteonecrosis before B.M.T. included, for the 2 patients, depression and fragmentation of the articular surface. MRI imaging of the bones of these patients observed before B.M.T. a decreased signal intensity relative to subcutaneous fat on the short TR/TE images instead of the high signal intensity of the usual fatty marrow in epiphysis.

Only three months after the B.M.T., osteonecrosis appeared to have healed without deformity for the two patients. Furthermore, MRI imaging of the bones at three months after B.M.T. observed a high signal intensity in the epiphysis corresponding to a yellow marrow.

Because of the stress on the marrow system in children with severe chronic hemolytic anemia, red marrow remains hyperplastic and extensive throughout the body and normal red marrow conversion to fat marrow is postponed in S.C.D.; marrow infarction in S.C.D. develops in red marrow; since red marrow persists in the epiphysis in S.C.D., these patients have these sites for potential infarction. Our observation shows MRI changes in the epiphysis and diaphysis marrow after B.M.T.; the appearance of the marrow changes after transplantation in these patients may reflect hemodynamic and physiologic phenomena attributable to the combined effects of the pretransplant chemotherapy and new bone marrow reconstitution after transplantation. This tendency of normalization of the epiphysis with red-yellow marrow conversion after B.M.T. is important since it is a reduction of the potential sites for infarction. This red-yellow marrow conversion after B.M.T. may also explain the velocity of the reconstruction of the epiphysis after osteonecrosis; if osteonecrosis may heal without deformity in the prepubertal epiphysis of children, it takes usually 5 or 6 years and this phenomena is very uncommon; healing was here observed only 3 weeks after B.M.T.; the effect of the B.M.T. on the reconstruction of the epiphysis may be explained by the following hypothesis: hematopoietic marrow of the epiphysis in S.C.D. had a rich sinusoidal system fed by several epiphyseal vessels; blood flow in the sinusoidal system is sluggish and the biochemical environment in this area facilitates the sickling process; blood containing sickled cells had high viscosity and produces a relative obstruction to blood flow in the sinusoidal system of the epiphysis. When sickled red cells are replaced with normal cells after B.M.T., bone circulation in the epiphysis is restored and allowed quick reconstruction when osteonecrosis is present.

This study seems to demonstrate that bone abnormalities associated with S.C.D. are reversible after B.M.T., phenomena of critical importance to support the eventual role B.M.T. as a curative treatment in S.C.D.