Periodic acid-schiff staining: A counterpart of the immunoreactivity seen by direct immunofluorescence in bullous pemphigoid

Periodic-Acid-Schiff (PAS) stain has been put forward to differentiate between bullous pemphigoid (BP) and epidermolysis bullosa acquisita (EBA). PAS stain shows correspondence with DIF staining patterns of EBA and BP with respect to basement membrane staining. Histological hall-mark of this entity is subepidermal blister containing eosinophils. But there can be other findings observed in this entity which can cause pitfalls in the diagnosis. Our study demonstrates these rare findings to avoid the misdiagnosis. To study the utility of Periodic-acid-Schiff stain in differentiating BP and EBA on histopathology. To evaluate ‘n’ versus ‘u’ serration patterns in differentiating BP and EBA on DIF examination. Two skin punch biopsies measuring 3 mm were obtained. Of the two skin punch biopsies, one was sent in Michel’s medium for direct immunofluorescence (DIF) and the other for light microscopy. PAS stain was performed on light microscopy. 18 (100%) clinically suspected cases of BP were assessed for light microscopy and DIF, of which 16 (88%) cases were confirmed by DIF examination and histopathology. 16 of them (88%) showed both floor pattern and basal fraying of keratinocytes. 4 (25%) cases showed a unique finding of linear arrangement of neutrophils along the basal layer of epidermis with subepidermal bulla containing eosinophils. Small sample size, inability to apply population based statistics and absence of the comparable group (EBA) due to which the findings may not be specific to the disease entity. PAS stain can be used to provide simple, cost-effective and reliable diagnosis in differentiating BP versus EBA cases, although indirect immunofluorescence remains the gold standard test for confirmation. BP should be differentiated from other subepidermal diseases to avoid the diagnostic pitfalls and misdiagnosis of the same, as neutrophils can also be present in BP as the main inflammatory cells and share some similar histological features with the other subepidermal diseases.