During a routine clinic visit, a 62-year-old male veteran complains of severe, widespread itching that reliably occurs within minutes of stepping out of a warm shower. He also reports recent onset of headaches and a sensation of fullness in his head. Physical examination reveals a ruddy facial complexion and a palpable spleen edge extending cm below the left costal margin. Laboratory studies reveal:
| Test | Value |
|---|---|
| Hemoglobin | g/dL |
| Leukocytes | /mm³ |
| Platelets | /mm³ |
Which of the following is the most appropriate next diagnostic step for this patient?
- AArterial blood gas measurement
- BInitiation of broad-spectrum antibiotics
- Peripheral blood mutation analysis for JAK2Answer
- DBone marrow aspiration and biopsy
- EReassurance and oral fluid hydration
Answer
Peripheral blood mutation analysis for JAK2 is the most appropriate next diagnostic step to confirm suspected Polycythemia Vera.
The patient's presentation of aquagenic pruritus (itching specifically after hot showers), facial plethora, splenomegaly, and panmyelosis (elevated erythrocytes, leukocytes, and platelets) is the classic triad of findings for Polycythemia Vera (PV). PV is a clonal myeloproliferative disorder driven primarily by a somatic mutation in the Janus kinase 2 (JAK2) gene, resulting in constitutive tyrosine kinase activity and EPO-independent proliferation of myeloid cells. The most appropriate initial diagnostic step is peripheral blood testing for the JAK2 V617F mutation (present in of cases), typically ordered alongside a serum erythropoietin level (which would be low).
Step-by-Step Solution
Key Concept
Polycythemia vera presents with hyperviscosity symptoms, aquagenic pruritus, splenomegaly, and panmyelosis, and is initially diagnosed via non-invasive peripheral blood JAK2 mutation analysis.