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A four year-old male with sickle cell anemia (HbSS) and persistence of fetal hemoglobin (HbF = 17%) was admitted with dyspnea in the setting of a three day history of fever, cough, congestion, and palpebral swelling.  Physical examination was remarkable for bilateral cervical lymphadenopathy and hepatomegaly.  Laboratory values during this hospitalization showed a below baseline hemoglobin level (4.4 g/dL), leukocytosis (43.5 K/µL), and thrombocytosis (411 K/µL).  Absolute reticulocyte count (273 K/µL) was suboptimal for the degree of anemia. Peripheral blood smear showed leukocytosis with neutrophilic left-shift, lymphocytosis with reactive lymphoid forms, and monocytosis with rare erythrophagocytosis.  Bone marrow biopsy was performed in order to rule out hematopoietic malignancy in the setting of new-onset lymphadenopathy and hepatomegaly.  The bone marrow was >90% cellular with progressively maturing trilineage hematopoiesis, and prominent emperipolesis within megakaryocytes (Image).  Blood culture collected the day of admission grew Moraxella catarrhalis.  Given the microbiology finding, continued antibiotic treatment with ceftriaxone was provided on inpatient basis.    Seven days after the admission, the patient's follow-up blood culture was negative, and significant improvement in signs and symptoms was noted.  His clinical and laboratory status remained stable on follow-up outpatient visits. 

The incidental megakaryocytic emperipolesis within the bone marrow of this patient was attributed to the acute inflammatory state as evidenced by leukocytosis and thrombocytosis.  Megakaryocytic emperipolesis has been described in patients with myeloproliferative and reactive thrombocytosis (Cashell and Buss, 1992).   Furthermore, reduction in GATA1 protein expression has been associated with neutrophil emperipolesis, particularly in presence of immature megakaryocytes and thrombocytopenia (Centurione et al., 2004).  While the clinical presentation and morphologic findings within the bone marrow favored a transient, reactive etiology in this case, the importance of considering deletion of megakaryocytic-specific regulatory sequences of GATA1 in association with significant neutrophil emperipolesis within megakaryocytes is emphasized.

Cashell AW, Buss DH. The frequency and significance of megakaryocytic emperipolesis in myeloproliferative and reactive states. Ann Hematol. 1992;64: 273-276.

Centurione L, Di Baldassarre A, Zingariello M, et al. Increased and pathologic emperipolesis of neutrophils within megakaryocytes associated with marrow fibrosis in GATA-1low mice. Blood. 2004;104 (12): 3573–3580.