Cocktail of Periodic Acid–Schiff and Papanicolaou: Novel staining technique for the identification of leukemic eosinophils – A pilot study

BACKGROUND: Tissue eosinophilia may be caused due to reactive, neoplastic or idiopathic reasons. Reactive eosinophils in allergic and inflammatory conditions are transient and recruited from the circulation in response to various stimuli, whereas neoplastic eosinophils of leukemias and hematological malignancies are involved in the pathogenesis of the disease. The differentiation of reactive from neoplastic eosinophils has a serious implication on the treatment and prognosis of diseases. However, both these types of eosinophils display variation in morphology and staining characteristics in routine histopathology leading to a diagnostic dilemma. AIM: The aim of this study is to evaluate the efficacy of special stains for the demonstration of eosinophils in normal/reactive lesions and leukemias. METHODOLOGY: A retrospective study comprising twenty histologically diagnosed cases each of reactive oral lesions and leukemias were obtained from institutional archives. These tissue sections were subjected to staining with routine and special stains – Carbol chromotrope, Congo red, Leishman's stain, Periodic Acid–Schiff-papanicolaou (PAS-PAP) and PAS. Statistical analysis was performed using Pearson's Chi-square test to compare the various parameters in the evaluation of the staining efficacy. RESULTS: Carbol chromotrope and Congo red staining showed increased staining efficacy in normal/reactive eosinophils while PAS-PAP followed by PAS and Leishman's stain showed enhanced features such as homogenicity, specificity, increased staining intensity, enhanced nuclear and cytoplasmic details in leukemic eosinophils. CONCLUSION: Combined PAS-PAP is a novel and cost-effective staining technique in differentiating reactive and leukemic eosinophils. It is significant in recognizing leukemic eosinophils of routine biopsies and alerts the clinician to rule out any underlying malignancies.