Multilineage haematopoiesis in the cerebrospinal fluid of an infant

A 4-month-old girl presented with fever of unknown origin and restlessness. A lumbar puncture was performed in order to rule out meningitis. The cerebrospinal fluid (CSF) was clear, with normal protein and glucose levels. Cytological examination in the central laboratory revealed numerous immature myeloid cells (blasts 1%, myelocytes 2%, metamyelocytes 9%, banded neutrophils 12%) and normoblasts (37%) with an elevated total cell count of 0.139 cells/μL, prompting a haematological consultation to rule out central nervous system (CNS) involvement of acute leukaemia. Peripheral blood counts and differential showed a mild leucocytosis with absolute monocytosis and neutrophilia, consistent with infection, without signs of anaemia or thrombocytopenia. The inflammatory markers were unremarkable (C-reactive protein 1.7 mg/dL [<0.8 mg/dL], procalcitonin 1.1 ng/mL [<0.1 ng/mL]) and there was no biochemical evidence of cell lysis (lactate dehydrogenase 209 U/L [190–420 U/L]). The cytomorphologic examination of the CSF (magnification objective × 100; Wright–Giemsa stain) showed a distribution of myeloid (arrows, upper panels) and erythropoietic (arrowheads, lower panels) progenitor cells reminiscent of a normal bone marrow aspiration (all images). There were no signs of myelodysplasia, and megakaryocytes could not be found. Therefore, the result of the lumbar puncture was considered highly suggestive of an accidental penetration of the vertebral body, which resulted in a marrow contamination into the CSF rather than a true CNS infiltration. Consistent with this interpretation, microbiology studies of blood and CSF remained negative, and the patient was discharged without further complications. In infants, vertebral bone is relatively thin and contains abundant haematopoietic marrow; therefore, a bone marrow contamination of CSF is a very rare but recognised complication of lumbar puncture. It is mostly observed in early childhood1, 2 but also in older patients.3, 4 Awareness of this possibility is essential and examination by a haematologist/pathologist is helpful in order to avoid misinterpretation as central nervous system leukaemia or meningitis, potentially leading to unnecessary invasive investigations or treatment. No identifying information of the patient was used.