Sideroblastic Anaemia
This is a refractory anaemia defined
by the presence of many pathological ring sideroblasts in the bone marrow (Fig.
3.14). These are abnormal erythroblasts containing numerous iron granules
arranged in a ring or collar around the nucleus instead of the few randomly
distributed iron granules seen when normal erythroblasts are stained for iron.
There is also usually erythroid hyperplasia with ineffective erythropoiesis.
Sideroblastic anaemia is diagnosed when 15% or more of marrow erythroblasts are
ring sideroblasts. They can be found at lower numbers in a variety of
haematological conditions.
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Sideroblastic anaemia is classified
into different types (Table 3.8) and the common link is a defect in haem
synthesis. In the hereditary forms the anaemia is usually characterized
by a markedly hypochromic and microcytic blood picture. The most common
mutations are in the ALA‐S gene which is on the X chromosome.
Pyridoxal‐6‐phosphate is a coenzyme for ALA‐S. Other rare types include an
X‐linked disease with spinocerebellar degeneration and ataxia, mitochondrial
defects (e.g. Pearson’s syndrome when there is also pancreatic insufficiency),
thiamine‐responsive and other autosomal defects. The much more common form is refractory
anaemia with ring sideroblasts, which is a subtype of myelodysplasia (see
Chapter 16). Acquired reversible forms may be due to alcohol, lead and drugs,
e.g. isoniazid.
In some patients, particularly with
the hereditary type, there is a response to pyridoxine therapy. Folate
deficiency may occur and folic acid therapy may also be tried. Other
treatments, e.g. erythropoietin, may be tried in the myelodysplasia form (see
Chapter 16). In many severe cases, however, repeated blood transfusions are the
only method of maintaining a satisfactory haemoglobin concentration, and
transfusional iron overload requiring
iron chelation therapy becomes a major problem.
