Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (352 page)

   Patients with pruritus, erythromelalgia, transient visual disturbances, headaches, weakness, dizziness, gastrointestinal symptoms, and excessive sweating.

   Laboratory Findings

   
CBC
: elevated Hb, Hct, and red cell count; platelets and granulocytes, but neither monocytes nor lymphocytes are frequently elevated.

   
Red cell mass (RCM)
: elevated (requires isotope study availability); plasma volume is normal or elevated.

   
Blood gases
: O
₂
>92%.

   
Bone marrow
: Hyperplasia of erythroid, granulocytic, and megakaryocytic lines, without increase in immature cells; decreased iron stores; increased reticulin, especially as the disease progresses. Absence of stainable iron is a nearly universal finding.

   
Molecular genetics
: V617F JACK2 mutation in the exon 14 is present in 95–97% of PV patients, but it is not specific for PV as it may also be present in essential thrombocythemia and primary myelofibrosis. Increasing amounts of V617F allele correspond to a more pronounced myeloproliferative phenotype, favoring higher Hb levels and leukocyte counts. Other mutations seen in a minority of patients include mutations, insertions, or deletions in exon 12 of the JACK2 gene.

   
Cytogenetics or FISH
: Absence of BCR-ABL1 (t(9;22)). Other abnormalities that may be found but are not specific for PV include 20q
⁻
, +8, +9, and gain of 9p.

   
Serum erythropoietin
: low or immeasurable.

   
Other
: Leukocyte alkaline phosphatase and serum vitamin B
₁₂
are elevated, but not necessary for diagnosis.

Suggested Reading

Passamonti F. How I treat polycythemia vera.
Blood.
2012;120:275–284.

ESSENTIAL THROMBOCYTHEMIA (ET)

   Definition

ET is a chronic myeloproliferative neoplasm (MPN) involving mainly the megakaryocytic lineage, characterized by persistent thrombocytosis. It is a diagnosis of exclusion.

   Who Should Be Suspected?