This week, we covered a series of cases in various clinical settings with patients presenting with very high white cell counts (>50 x 109 / L). The differential diagnosis is wide, including both haematological (hyperleukocytosis) and non-haematological (leukemoid reactions) causes. Rarely, a high WCC represents a haematological emergency and requires emergency treatment.
Leukemoid reaction vs CML
| Leukemoid reaction | Chronic myeloid leukaemia | |
| Definition | WCC >50 x 109 / L due to non-leukaemic causes | Myeloproliferative neoplasm => uncontrolled production of granulocytes |
| Aetiology | serious infections/sepsis, drugs (e.g. G-CSF), solid organ malignancy | BCR-ABL1 fusion gene (Ph chromosome) |
| Clinical features | clear precipitant (e.g. severe sepsis), patient is usually very unwell due to underlying cause | usually relatively well (unless in blast crisis), incidental finding, splenomegaly, fatigue, weight loss |
| Pathologic features | neutrophilia, left shifted granulocytes, toxic granulation of neutrophils | leukocytosis (often >100) with neutrophilia, basophilia (universal finding) and eosinophilia, left shifted granulocytes, “myelocyte bulge”, normocytic anaemia, thrombocytosis |
Causes of hyperleukocytosis (leukaemic WCC >50 x 109 / L)
Mature lymphoid neoplasms: CLL, indolent NHLs (e.g. marginal zone, follicular), B- and T-PLL (rare and more aggressive)
Chronic myeloid neoplasms: CML, CMML, other rare myeloproliferative neoplasms (e.g. chronic neutrophilic leukaemia)
Acute lymphoblastic leukaemia
Acute myeloid leukaemia: FLT3 mutated, myelomonocytic/monocytic subtypes
Complications of hyperleukocytosis
Epidemiology: Complications of hyperleukocytosis usually affect patients with AML or ALL. They are very uncommon in patients with CLL and CML (with the exception of CML in blast crisis). Symptoms more commonly occur with a blast count > 100 x 109 / L.
Disseminated intravascular coagulation: can occur in either ALL or AML
Tumour lysis syndrome: more common in ALL than AML, usually complication of treatment but can occur spontaneously
Leukostasis: more common in AML than ALL, respiratory features (pulmonary infiltrates, hypoxaemia), neurological features (visual blurring, confusion, headahes, reduced GCS), associated with early mortality
Management of symptomatic hyperleukocytosis: supportive care (fluids, rasburicase, avoid red cell transfusions if possible) and cytoreduction (one or more of hydroxurea, leukapheresis, induction chemotherapy)
