Differential Diagnosis for CML

The question requires a differential diagnosis to distinguish Chronic Myeloid Leukemia (CML) from other myeloproliferative neoplasms such as polycythemia vera, essential thrombocythemia, and primary myelofibrosis. The correct answer and its justification are provided below, categorized for clarity.

• Single most likely diagnosis:

  • A. t(9;22) BCR–ABL: This is the single most likely diagnosis because the presence of the Philadelphia chromosome, resulting from the t(9;22) translocation and leading to the BCR-ABL fusion gene, is pathognomonic for CML. It is a specific and sensitive marker that distinguishes CML from other myeloproliferative disorders.

• Other Likely diagnoses:

  • C. Leukocytosis: While leukocytosis (an increase in white blood cell count) is a common feature of CML, it can also be seen in other conditions such as leukemoid reactions, infections, and other myeloproliferative neoplasms. Thus, it is not specific enough to differentiate CML from the other conditions listed but is a common finding.
  • D. Splenomegaly: Splenomegaly (enlargement of the spleen) can occur in CML due to the accumulation of leukemic cells, but it is also a feature of other myeloproliferative neoplasms like polycythemia vera, essential thrombocythemia, and primary myelofibrosis. Therefore, it is not a distinguishing feature.

• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.):

  • None specifically listed in the options provided, as the key distinguishing feature (t(9;22) BCR-ABL) is already identified. However, in the broader context of diagnosing CML, it's crucial not to miss the diagnosis of CML itself due to its specific treatment implications, including targeted therapy with tyrosine kinase inhibitors.

• Rare diagnoses:

  • B. Thrombocytosis: While thrombocytosis (an increase in platelet count) can be seen in CML, especially in the early phases, it is more characteristic of essential thrombocythemia. In the context of differentiating CML from other myeloproliferative neoplasms based on the provided options, thrombocytosis is not the most specific or sensitive marker for CML.

In summary, the presence of t(9;22) BCR-ABL is the key feature that differentiates CML from polycythemia vera, essential thrombocythemia, and primary myelofibrosis.