Auer rods are cytoplasmic crystals seen in acute myelogenous leukemia (AML). Pseudo-Auer rods are cytoplasmic crystals seen in lymphoproliferative disorders. It is important to identify these correctly, since they are associated with a significantly different prognosis.
True Auer rods represent crystallization of azurophilic granules.
Pseudo-Auer rods are crystals or pseudocrystals of other proteins. This may include immunoglobulins and possibly lysosomal proteins (Castoldi et al).
Pseudo-Auer rods have been reported in:
(1) CLL
(2) prolymphocytic leukemia
(3) multiple myeloma
Differential staining:
(1) myeloperoxidase and Sudan Black B
(2) immunoglobulins (usually IgA, IgM, IgG)
Myeloperoxidase or Sudan Black B
Immunoglobulins
Diagnosis
positive
negative
Auer rods of AML
negative
positive, negative
pseudo-Auer rods
Alternatively immunoperoxidase stains can be done for differential staining of lymphocyte vs myeloid series cell. However, interpretation may be difficult if the leukemic cell expresses both myeloid and lymphoid markers.
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