Auer rod

Auer rods—also known as Auer bodies—are distinctive, crystalline cytoplasmic inclusion bodies that can be identified in the myeloid blast cells of certain hematological diseases. Their presence is particularly associated with acute myeloid leukemia (AML), acute promyelocytic leukemia (APL), as well as high-grade Myelodysplastic Syndromes and Myeloproliferative Disorders.

AML M2 with Auer rods

Composition and Structure

Auer rods are composed of fused lysosomes and are rich in lysosomal enzymes. They are azurophilic, meaning they stain readily with the Romanowsky type dyes due to their affinity for acidic dyes like eosin. Morphologically, Auer rods can resemble various shapes such as needles, commas, diamonds, rectangles, corkscrews, or, though rarely, granules.

Pathophysiology

The formation of Auer rods is not fully understood, but they are considered to be a byproduct of abnormal myeloid cell development and differentiation seen in certain hematologic malignancies. They are abnormal accumulations of peroxidase-positive material, such as Myeloperoxidase, that are typically not found in normal leukocytes.

Clinical Significance

The presence of Auer rods in myeloid precursors is a pathognomonic sign of a pathological process and is critical in the diagnosis of certain types of leukemia. Their detection often involves a bone marrow examination and cytochemical staining, and is an important criterion in the French-American-British (FAB) Classification system used to classify AML.

Associated Conditions

• Acute Myeloid Leukemia
• Acute Promyelocytic Leukemia
• High-grade Myelodysplastic syndromes
• Myeloproliferative disorders

Detection and Examination

Auer rods are detected through microscopic examination of blood or bone marrow samples. They are especially visible under light microscopy in cells stained with Romanowsky stains, such as Wright's or Giemsa stain. In some cases, they may be seen in peripheral blood smears, but they are more commonly found during bone marrow analysis.

Prognostic Value

In some types of leukemia, the presence of Auer rods may have prognostic implications, aiding in risk stratification and treatment planning.

In Medical Education

The identification of Auer rods is a key component of medical education in Hematology and Pathology, training healthcare professionals to recognize important diagnostic features of hematological disorders.

Gallery

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  Bone marrow aspirate showing acute myeloid leukemia with Auer rods in several blasts

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