# Morphological Clues of Acute Monocytic Leukemia in COVID-19-Induced Transient Leukoerythroblastic Reaction with Monocytosis

## TL;DR

A patient with severe COVID-19 showed blood changes resembling leukemia, but further testing revealed actual acute myeloid leukemia.

## Contribution

This case highlights the need for thorough testing to distinguish between reactive blood changes and true leukemia in patients with severe viral infections.

## Key findings

- A patient with severe COVID-19 had transient monocytosis with promonocytes, but no cytopenia.
- Molecular testing revealed pathogenic mutations consistent with acute myeloid leukemia despite normal blood counts.
- Promonocytes in peripheral blood were later confirmed as part of a leukemic process, not a reactive change.

## Abstract

Viral infections, including those caused by COVID-19, can produce striking morphologic changes in peripheral blood. Distinguishing between reactive changes and abnormal morphology of monocytes remains particularly difficult, with low consensus rates reported amongst hematopathologists. Here, we report a patient who developed transient monocytosis of 11.06 × 109/L with 32% promonocytes and 1% blasts during hospitalization that was secondary to severe COVID-19 infection. Three days later, the clinical status of the patient improved and the WBC had decreased to 8.47 × 109/L with 2.2 × 109/L monocytes. Flow cytometry studies did not reveal immunophenotypic findings specific for an overt malignant population. At no time during admission did the patient develop cytopenia(s), and she was discharged upon clinical improvement. However, the peripheral blood sample containing promonocytes was sent for molecular testing with an extended next-generation sequencing myeloid panel and was positive for pathogenic NPM1 Type A and DNMT3A R882H mutations. Subsequently, despite an essentially normal complete blood count, the patient underwent a bone marrow assessment that showed acute myeloid leukemia with 77% promonocytes. This case emphasizes the critical importance of a full work up to exclude acute leukemia when classical promonocyte morphology is encountered in the peripheral blood. Promonocytes are not a part of the reactive changes associated with COVID-19 and remain specific to myeloid neoplasia.