Aplastic anemia

Aplastic anaemia is a rare haematopoietic stem-cell disorder. The condition results in pancytopaenia and hypocellular bone marrow. Most cases are acquired, however there are unusual inherited forms.

Pathophysiology

Aplastic anaemia manifests as a marked reduction in the number of pluripotent haematopoietic stem cells. It is immune-mediated in most cases where autoreactive lymphocytes mediate the destruction of haematopoietic stem cells. Environmental exposures (e.g. drugs, viruses, and toxins) are thought to initiate the aberrant immune response in some patients, but most cases are classified as idiopathic.

Radiographic features

MRI

Signal characteristics follow differences in fatty versus haematopoetic marrow.  Reported patterns include ³:

• focal low-signal (both TI and T2) areas (likely representing islands of active haematopoietic cells) interspersed with high-SI areas in the marrow of the spine. Note this pattern is also seen in lymphoma, metastases and myeloma.
• diffuse high-signal marrow without focal abnormalities in pelvis and proximal femoral regions

MRI is also useful for assessment of response to treatment in aplastic anaemia as well as other haematopoietic disorders⁴.

Complications

• development ofparoxysmal nocturnal haemoglobinuria (PNH)
• development of myelodysplastic syndrome
• osteonecrosis of the hip⁸

Treatment and prognosis

Similar to other autoimmune diseases, aplastic anaemia has a varied clinical course which ranges from some patients having mild symptoms that necessitate little or no therapy to others presenting with life-threatening pancytopenia. Acquired aplastic anaemia can be effectively treated by allogeneic bone-marrow transplantation, immunosuppression (generally antithymocyte globulin and cyclosporin), and high-dose cyclophosphamide.