<s>[INST] context: Analyzing all the options one by one;
Option ‘a’…direct quote.. ‘about 5% to 10% of patients eventually develop acute myeloid leukemia or a myelodysplastic syndrome, possibly because hematopoietic stem cell have suffered some type of genetic damage’. (Robbins 8th/653) Even PNH is associated with aplastic anemia as both the disorders have an autoimmune basis.
Option ‘b’…direct quote.., aplastic anemia results from a fundamental stem cell defect supported by the presence of karyotypic aberrations in many cases; the occasional transformation of aplasias into myeloid neoplasms, typically myelodysplasia or acute myeloid leukemia; and the association with abnormally short telomeres. (Robbins 8th/664)
Option ‘d’…direct quote.. The term “myelodysplastic syndrome” (MDS) refers to a group of clonal stem cell disorders characterized by maturation defects that are associated with ineffective hematopoiesis and a high risk of transformation to AML. (Robbins 8th/625).
So the answer of exclusion is PCH (paroxysmal cold hemoglobinuria). It is an autoimmune haemolytic anemia due to IgG autoantibodies which bind to P blood group antigen and cause intravascular hemolysis and hemoglobinuria. Most cases are seen in children and have recovery within a month.....Wintrobes. [/INST] question: Which of the following is the least likely to be a preleukaemic condition? | options: A: Paroxysmal nocturnal haemoglobinuria B: Aplastic anaemia C: Paroxysmal cold haemoglobinuria D: Myelodysplastic syndrome | answer: C </s>