Auer Rods: When Leukemia Shows Up Differently
"Unusual presentation of leukemia in a child reveals the importance of recognizing atypical signs"
Leukemia, a cancer of the blood, often presents with a complex array of symptoms and diagnostic markers. While certain indicators are commonly observed, the disease can sometimes manifest in unexpected ways, confounding initial assessments and requiring a keen eye for detail.
A recent case study highlights such an instance, detailing the unique presentation of mixed phenotype acute leukemia (MPAL) in an 11-year-old boy. This case underscores the importance of recognizing atypical signs and symptoms that deviate from the norm, potentially leading to earlier and more accurate diagnoses.
The conventional understanding of leukemia involves the presence of Auer rods, crystalline inclusions found within the cytoplasm of immature blood cells called blasts. However, this case defies expectations by reporting the presence of Auer rods in mature neutrophils, a phenomenon rarely encountered and prompting a reevaluation of diagnostic approaches.
How Auer Rods Are Identified
John Auer first described needle- or rod-shaped inclusions in leukemia cells in 1906. Auer rods may occur in myeloid neoplasms, from acute myeloid leukemia (AML) to myelodysplasia, and are not seen in normal or non-neoplastic reactive states. In a review of 125 AML cases, Wright-Giemsa staining recognized Auer rods in 20.8% of cases, while peroxidase staining detected them at about three times that rate. This difference shows that detection depends on the staining method used.
From Auer’s Observation to a Defining Sign
A 2025 illustrated review says Dr. John Auer first observed needle-like rods in 1903, initially mistaking them for lymphocytes in a patient with fever, coagulopathy, and splenomegaly. They were later identified in myeloblasts and became a defining feature of myeloid malignancies. Acute promyelocytic leukemia (APL) was recognized as a distinct clinical entity in 1957. Auer rods are not entirely exclusive to myeloid malignancies: a 2009 review notes rare Auer rod–like inclusions in neoplastic cells in B-cell malignancies, including chronic lymphocytic leukemia/small lymphocytic lymphoma.
What Makes This Leukemia Case Unique?
The 11-year-old patient was admitted to the emergency department displaying persistent circumoral impetigo, a skin infection around the mouth. Further examination revealed additional symptoms, including skin pallor, enlarged lymph nodes, and hepatosplenomegaly (enlargement of the liver and spleen). Blood tests indicated an elevated white blood cell count (32.5 × 10º/l), low hemoglobin levels (90 g/l), and a platelet count of 220 × 10°/l, with 73% circulating blasts, signaling a potential hematological malignancy.
- Peripheral blood (top images) and bone marrow (bottom images)
- 90% CD45weak, CD34+ and HLA-DR+
- Myeloid markers CD13, CD117 and myeloperoxidase.
- T-cell markers: CD2, CD99 and cytoplasmic CD3. CD4 and CD8 expression were absent
- TP53 mutation and WT1 overexpression were present
Unusual Presentations in Recent Reports
A report by Hrusak, Stancikova, Vodickova, and colleagues describes 11 cases of Auer rod-positive acute leukemia with a predominantly lymphoid immunophenotype. Another recent report describes “faggot-like” Auer rod aggregation in AML blasts as uncommon and potentially misidentified as abnormal promyelocytes; the snippet also notes strong peroxidase positivity. A 2024 Blood case report describes an automated analyzer flagging a blood sample, followed by a smear review that noted Auer rod–like inclusions in a B-cell lymphoma case. These reports illustrate atypical appearances and diagnostic contexts, rather than establishing how frequently they occur.
Auer Rods Do Not Settle Lineage on Their Own
A report describes three cases of mixed-phenotype acute leukemia (MPAL), T/myeloid, with Auer rods identified in blasts. This shows that Auer rods can appear in a leukemia classified as mixed phenotype, rather than serving as a complete account of lineage by themselves. A separate report on cytochemically myeloid, early T-cell precursor acute lymphoblastic leukemia notes that the WHO classification did not specify the exact myeloperoxidase (MPO) positivity cutoff required to establish myeloid lineage. The source therefore highlights uncertainty around a specific classification threshold.
Morphology and Immunophenotype Can Diverge
In one B-acute lymphoblastic leukemia case, flow cytometry found MPO positivity in approximately 50% of bone-marrow blasts, while the marrow immunophenotype otherwise resembled that in peripheral blood. A separate international cohort reported 11 children with Auer rods and significant T-cell and myeloid markers: seven were categorized as early T-cell precursor (ETP), two as T-ALL with ETP status unknown, one as acute leukemia of ambiguous lineage (ALAL), and one as AML reclassified from ALAL. Together, these source-specific findings show that Auer rods or myeloid markers may occur in cases with lymphoid or ambiguous-lineage features. They do not establish that these findings alone determine a diagnosis.
Why Does This Matter?
This case emphasizes the importance of maintaining a broad differential diagnosis and considering atypical presentations, especially in cases of leukemia. While Auer rods are typically associated with blasts, their presence in mature neutrophils should prompt further investigation and consideration of MPAL. Recognizing such deviations from the norm can lead to more timely and accurate diagnoses, ultimately improving patient outcomes. Further research is needed to fully understand the mechanisms driving Auer rod formation in mature neutrophils and the clinical implications of this unusual phenomenon.
A Predominantly Myeloid Association, with Exceptions
Auer rods are described as prominent intracellular structures found almost exclusively in myeloid cell malignancies, including AML and chronic and juvenile myelomonocytic leukemia. The phrase “almost exclusively” leaves room for exceptions rather than making the association absolute. The 11-case report on acute leukemia with a predominantly lymphoid immunophenotype provides a specific example of Auer rods occurring alongside substantial lymphoid features. These source materials support treating the finding as strongly associated with myeloid malignancy while recognizing atypical cases.
APL’s Historical Diagnostic Significance
A 2025 illustrated review describes Auer rods as a defining feature of myeloid malignancies and identifies acute promyelocytic leukemia (APL) as a distinct clinical entity recognized in 1957. It reports that APL was once considered the most lethal acute leukemia because of severe coagulopathy and alarmingly high early mortality. A separate LinkedIn article associates Auer rods most commonly with AML, particularly French-American-British (FAB) subtypes M1 to M6. These sources provide historical and classification context, but do not specify future research directions.
A Specific Finding in Myeloid Neoplasia
A ScienceDirect overview describes Auer rods as red, needle-like crystals containing peroxidase. It characterizes them as an occasional but highly specific finding for a myeloid neoplastic disorder. The overview illustrates them in acute myelogenous leukemia and alongside ringed sideroblasts in myelodysplasia. Its description emphasizes specificity, while noting that the finding is occasional.
Rare Findings in Individual Cases
A case report describes the concurrent presence of Auer rods and pseudo-Chediak–Higashi anomaly as exceptionally rare. It highlights monoblastic morphology in a therapy-related context as part of the case’s significance. Another report notes that Auer rods in maturing myeloid cells and monocytes are rare, and documents a case of Auer rods in polymorphs in AML. These reports describe unusual individual presentations, not their frequency across patients.