What is the most likely diagnosis for a patient with headaches, visual disturbances, itchy rash after hot baths, ruddy complexion, palpable spleen, and lab results showing elevated packed red cell volume, white cell count, and thrombocytosis?

Diagnosis: Polycythemia Rubra Vera (Answer D)

This patient has polycythemia rubra vera (PV), a myeloproliferative neoplasm characterized by the classic triad of elevated red cell mass, aquagenic pruritus (itchy rash after hot baths), and splenomegaly, along with the characteristic ruddy (plethoric) complexion. 1

Clinical Features Supporting PV Diagnosis

The patient presents with the hallmark features of polycythemia vera:

• Elevated packed red cell volume with raised cell mass - This meets the primary major criterion for PV diagnosis (hemoglobin >16.0 g/dL in women or hematocrit >48% in women) 1

• Aquagenic pruritus - The itchy rash after hot baths is pathognomonic for PV, occurring in approximately 48% of patients and represents a non-life-threatening but characteristic complication 1

• Palpable splenomegaly - Present due to extramedullary hematopoiesis and is a common finding in PV 1

• Ruddy complexion (plethora) - The characteristic facial appearance results from increased red cell mass and is highly suggestive of PV 2

• Thrombocytosis and leukocytosis - The raised white cell count (leukocytosis occurs in 49% of PV cases) and thrombocytosis indicate trilineage myeloproliferation, which is characteristic of PV 1, 2

• Microvascular disturbances - Headaches and visual disturbances represent microvascular complications from hyperviscosity and are common presenting symptoms 1

• History of gout - This is consistent with increased cell turnover in myeloproliferative disorders 1

Why Other Options Are Incorrect

Chronic myeloid leukemia (CML) would typically present with marked leukocytosis with left shift, basophilia, and the Philadelphia chromosome (BCR-ABL1), not the combination of aquagenic pruritus and predominantly erythrocytosis 1

Lymphoma does not cause polycythemia or aquagenic pruritus, and would present with lymphadenopathy rather than this specific constellation of findings 1

Migraine with aura cannot explain the hematologic abnormalities, splenomegaly, ruddy complexion, or aquagenic pruritus 1

Soap allergy would not cause post-bath pruritus specifically (aquagenic pruritus occurs with water contact regardless of soap), nor would it explain any of the hematologic or physical examination findings 1

Diagnostic Confirmation Required

According to WHO 2016 criteria, PV diagnosis requires either all 3 major criteria OR the first 2 major criteria plus the minor criterion 1:

Major Criteria:

1. Elevated hemoglobin (>16.0 g/dL in women) or hematocrit (>48% in women) - PRESENT 1
2. Bone marrow biopsy showing hypercellularity with trilineage growth and pleomorphic megakaryocytes - NEEDS CONFIRMATION 1
3. Presence of JAK2 V617F or JAK2 exon 12 mutation - NEEDS TESTING 1

Minor Criterion:

• Subnormal serum erythropoietin level (specificity >90% for PV) - SHOULD BE TESTED 1, 2

Critical Next Steps

• JAK2 mutation testing (V617F or exon 12) is essential, as it is present in >95% of PV cases and is a major diagnostic criterion 1

• Serum erythropoietin level - A low level (sensitivity ~70%, specificity >90%) strongly supports PV diagnosis, while a high level suggests secondary polycythemia 1, 2

• Bone marrow biopsy with histology showing hypercellularity, trilineage myeloproliferation, and pleomorphic megakaryocytes would confirm the diagnosis 1

Management Implications

This diagnosis has significant implications for thrombosis risk and requires immediate treatment:

• Therapeutic phlebotomy to maintain hematocrit <45% (reduces thrombosis risk) 2
• Low-dose aspirin 81 mg daily for all patients unless contraindicated, which also treats the aquagenic pruritus and erythromelalgia 1, 2
• Risk stratification for cytoreductive therapy (hydroxyurea) if high-risk features present (age >60 years or prior thrombosis) 1, 2

The combination of aquagenic pruritus, splenomegaly, ruddy complexion, and pancytosis makes polycythemia rubra vera the definitive diagnosis in this clinical scenario.