Circulating Mature Megakaryocytes in an Unusual Case of BCR-ABL1-Positive CML

Dear Sir,

A 64-year-old male presented with weakness for 6 months. Examination revealed moderate pallor with massive splenomegaly. Hemoglobin was 87 g/l, total leukocyte count (TLC) 15.0 × 10⁹/l, and platelet count 787 × 10⁹/l. Leukocyte differential showed 88% neutrophils, 08% lymphocytes, 02% monocytes, 01% myelocytes and 01% metamyelocytes with 1 nucleated red cell per 100 leukocytes. Basophils were nil even on a 500-cell differential count. Red cells were normocytic normochromic with a few dacryocytes and codocytes. Strikingly, several circulating megakaryocytes, mostly with segmented nuclei, along with a few bare megakaryocytic nuclei (Fig. 1) were noted in the tail of the blood film. Cytochemical leukocyte alkaline phosphatase (LAP) score was 92 (control 256).

Fig. 1.

Circulating mature megakaryocytes with typical segmented nuclei, typically localized to the tail of the smears [May–Grünwald–Giemsa, at various magnifications]

Prior therapy was excluded by specific questioning. With a working diagnosis of essential thrombocythemia (ET) versus pre-fibrotic primary myelofibrosis (PMF), bone marrow (BM) was performed. Smears were aparticulate and diluted. However, trephine imprint smears revealed clusters of large megakaryocytes with hyperlobate nuclei along with small hypolobate forms. BM biopsy was hypercellular showing extensive megakaryocytic hyperplasia with both hypo- and hyper-lobate forms along with grade 2 reticulin fibrosis (EUMNET system). Granulocytic and erythroid elements were adequate.

The overall picture suggested a myeloproliferative neoplasm (MPN) with fibrosis, with chronic myeloid leukemia (CML) appearing unlikely due to the nearly-normal TLC, minimal left shift, absence of basophils and normal range LAP score. However, amplification refractory mutation system-polymerase chain reaction (ARMS-PCR) for the JAK2 V617F mutation was negative while multiplexed reverse transcriptase PCR for the BCR-ABL1 gene fusion revealed the e13a2 transcript (Fig. 2). Cytogenetic analysis divulged t(9;22)(q34;q11) in 12 out of 20 metaphases. The final diagnosis was CML, bcr-abl1-positive in chronic phase. Even as the investigations were underway, he was brought to the emergency in an unresponsive hypoventilatory state and found to be severely dehydrated with dilated cardiomyopathy and an ejection fraction of 15%. Attempts to resuscitate him using fluids and inotropes were unsuccessful and he expired the same day.

Fig. 2.

The reverse-transcriptase PCR gel (2% agarose) with the patient’s cDNA run in lane 1 showing a band corresponding to the bcr-abl1 e13a2 transcript for the p210 fusion protein

CML, especially in a full-blown case with massive splenomegaly and myelofibrosis, is often the easiest MPN to diagnose morphologically from the blood film itself, with its leucocytosis, mid-myeloid bulge and basophilia distinguishing it from the other MPNs. Our atypical patient however highlights that this may not always be the case. Basophilia is long known to be virtually universal in CML [1, 2] and a classic study that followed up atomic bomb survivors from Hiroshima, Japan found an early increase in basophils (two to five times the normal range) even before the development of other peripheral blood manifestations (like leucocytosis, left shifted neutrophils, thrombocytosis or low LAP) or clinical features [3].

Circulating megakaryocytes have long been described in healthy individuals [4], in preterm neonates [5] and in non-hematological malignancies [6]. Although circulating immature, hypolobate or dwarf megakaryocytes/megakaryoblasts are common in Indian CML patients according to one series [7], very few CML cases show an abundance of more mature, nearly normal-sized cells in blood films like this one. The causes of the marked megakaryocythemia could include fibrosis and/or as a pre-terminal event. In conclusion, this case illustrates the importance of the WHO classification’s mandatory diagnostic requirement for ET and PMF that “…criteria for BCR-ABL1-positive CML… are not met”, since morphology and blood counts can be deceptive in CML without molecular testing.

Conflict of interest

The authors declare that they have no conflict of interests.

Ethical Approval

All procedures performed in this report involving a human participant were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. This is a purely observational report and no research procedure was done.

Informed Consent

Informed consent has been obtained for this manuscript.