Auer Rod‐Like Inclusions in Chronic Lymphocytic Leukemia: A Case Report

ABSTRACT

Auer rod‐like inclusions may occasionally be observed in chronic lymphocytic leukemia. Their recognition on peripheral smear highlights the importance of meticulous morphology assessment when comprehensive hematologic testing cannot be performed.

1. Introduction

Peripheral blood smear review remains essential for identifying underlying hematologic disorders, especially when comprehensive diagnostic testing is limited. In elderly patients with lymphocytosis, careful morphology assessment can reveal clues suggestive of a clonal process. We report a patient with Auer rod‐like inclusions in lymphocytes on smear, which prompted further evaluation and led to the diagnosis of chronic lymphocytic leukemia (CLL).

Auer rods are cytoplasmic crystalline inclusions classically associated with acute myeloid leukemia (AML) and considered a hallmark of myeloid differentiation. Although their occurrence is exceedingly rare, isolated cases of Auer rod‐like inclusions have been reported in various B‐cell neoplasms, including CLL, prolymphocytic leukemia, B‐cell lymphoma, low‐grade B‐cell leukemia, and multiple myeloma [1, 2, 3, 4, 5, 6, 7, 8, 9]. Recognition of this rare morphologic phenomenon may help avoid misdiagnosis or underdiagnosis. This report provides valuable scientific context that enhances reader understanding and engagement.

2. Case History and Examination

An 88‐year‐old man presented with a 2‐month history of progressive dysphagia. Physical examination showed no pallor, no palpable superficial lymphadenopathy, no sternal tenderness, clear lung fields, a regular cardiac rhythm, and a soft abdomen without hepatosplenomegaly. Complete blood count revealed a white blood cell count of 13.2 × 10⁹/L, an absolute lymphocyte count of 8.45 × 10⁹/L, hemoglobin of 111 g/L, and a platelet count of 346 × 10⁹/L. Liver and renal function tests were normal, and ultrasonography demonstrated no superficial lymphadenopathy or hepatosplenomegaly.

Esophagogastroduodenoscopy identified a mass in the mid‐esophagus, and biopsy confirmed esophageal squamous cell carcinoma. In view of the lymphocytosis, a peripheral blood smear was performed. Detailed review showed numerous small mature lymphocytes with scant cytoplasm, condensed chromatin, and inconspicuous nucleoli. Approximately 80% of lymphocytes contained short, rod‐shaped, non‐staining Auer rod‐like inclusions located in the cytoplasm (Figure 1A, arrows) or the nucleus (Figure 1B, arrows).

FIGURE 1.

Morphologic and immunophenotypic features of the patient's peripheral blood cells. (A) Peripheral blood smear showing small mature lymphocytes with scant cytoplasm and dense chromatin, with short, rod‐shaped, non‐staining Auer‐like inclusions in the cytoplasm (Wright‐Giemsa stain, ×1000 magnification). (B) Peripheral blood smear demonstrating Auer‐like inclusions located within the nucleus of a lymphocyte (Wright‐Giemsa stain, ×1000 magnification). (C) Flow cytometric immunophenotyping of peripheral blood revealing a clonal B‐cell population expressing CD19, HLA‐DR, CD200, CD23, and λ light chain; weak CD5 and CD20; and negative CD79b, IgM, CD10, FMC7, and κ light chain, supporting a diagnosis of CLL/SLL.

3. Differential Diagnosis, Investigations, and Treatment

The differential diagnosis included reactive lymphocytosis, CLL, and other mature B‐cell neoplasms. As the patient's family declined bone marrow aspiration, peripheral blood flow cytometric immunophenotyping was performed (Figure 1C). A clonal B‐cell population accounting for 48.51% of nucleated cells was identified. The immunophenotype was positive for CD19, HLA‐DR, CD200, CD23, and λ light chain; weakly positive for CD5 and CD20; and negative for CD79b, IgM, CD10, FMC7, and κ light chain. This immunophenotypic profile was characteristic of CLL and helped exclude other mature B‐cell neoplasms, particularly mantle cell lymphoma, which typically shows strong CD5 expression, cyclin D1 overexpression, and negativity for CD23. The CLL score was 5, confirming the diagnosis of CLL/small lymphocytic lymphoma (SLL).

Given the patient's advanced age, his family declined further treatment for the esophageal carcinoma. As he did not meet established treatment criteria for CLL, periodic monitoring was recommended.

4. Conclusion and Results

The patient was diagnosed with CLL based on peripheral blood immunophenotyping after bone marrow evaluation was declined. As he remained asymptomatic and did not meet treatment criteria, a watch‐and‐wait approach was adopted. During follow‐up, his lymphocyte count and clinical status remained stable without progression, and no CLL‐related complications were observed. Importantly, the presence of Auer rod‐like inclusions did not alter the therapeutic strategy or clinical outcome in this patient. This case emphasizes the importance of peripheral smear evaluation in guiding diagnosis and clinical decision‐making when comprehensive diagnostic testing is limited.

5. Discussion

Rare and unexpected morphologic findings in hematologic malignancies can complicate diagnostic interpretation, and careful morphologic assessment, supplemented by flow cytometry when necessary, is essential for accurate identification [8, 9]. Auer rods are myeloperoxidase positive, whereas Auer rod‐like inclusions may lack myeloperoxidase or granule‐derived components and are thought to represent crystallized immunoglobulins [9, 10, 11]. In contrast to the needle‐shaped, azurophilic cytoplasmic inclusions described in most reported cases [2, 3, 4, 5, 6], the inclusions observed in the present case were short, rod‐shaped, and non‐staining. This atypical morphology likely reduced the risk of misclassifying as AML; however, further immunophenotypic or molecular studies are necessary to confirm the lineage and avoid diagnostic error.

The significance of Auer‐like inclusions in lymphoid cells remains uncertain, and these inclusions should not be overinterpreted as evidence of myeloid differentiation. Mathur et al. reported that Auer rod‐like inclusions in plasma cells of multiple myeloma were negative for myeloperoxidase (MPO) and Sudan black B (SBB), confirming that they do not reflect true myeloid differentiation [5]. Their presence has been postulated hypothetically to reflect underlying genomic instability, biclonal hematopoiesis, or an increased susceptibility to therapy‐related myeloid neoplasms [12]. In the present case, the coexistence of solid tumor malignancy in an elderly patient may suggest a higher background genomic vulnerability; however, this remains speculative, as advanced molecular assessments, such as next‐generation sequencing, were not performed.

Auer rods are associated with prognosis and subtypes in myeloid malignancies, particularly in myelodysplastic syndromes [13, 14, 15]. In contrast, the impact of Auer rod‐like inclusions in B‐cell neoplasms on prognosis has not been reported. In the present case, Auer rod‐like inclusions did not influence clinical treatment or prognosis. The patient did not meet the treatment criteria for CLL and was managed with a watch‐and‐wait approach. During follow‐up, the lymphocyte count remained stable. This suggests that while these inclusions represent a noteworthy morphological feature, they may not affect the prognosis.

Finally, we acknowledge that, due to limited sample availability, MPO cytochemical staining was not performed, which represents a limitation of this study. The absence of MPO results precludes the complete exclusion of myeloid features, and this should be taken into consideration when interpreting our findings.

In summary, this case underscores the diagnostic value of meticulous peripheral blood smear examination. In elderly patients, mild lymphocytosis is often misinterpreted as reactive, making careful morphological assessment crucial to avoid misdiagnosis. In this case, the presence of Auer rod‐like inclusions on the smear suggested an underlying monoclonal lymphoproliferative disorder, which was ultimately confirmed as CLL through flow cytometric immunophenotyping. This case highlights the importance of recognizing these inclusions on peripheral smear for accurate diagnosis.

Author Contributions

Linjun Xie: conceptualization, visualization, writing – review and editing. Tingting Zhang: writing – original draft.

Funding

The authors have nothing to report.

Consent

We have obtained the written informed consent from the patient's family.

Conflicts of Interest

The authors declare no conflicts of interest.

Zhang T. and Xie L., “Auer Rod‐Like Inclusions in Chronic Lymphocytic Leukemia: A Case Report,” Clinical Case Reports 14, no. 2 (2026): e71955, 10.1002/ccr3.71955.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.