Characterizing "blue blobs" - Immunohistochemical staining and ultrastructural study

OBJECTIVE: To investigate the nature and origin of "blue blobs" (Bbs) in at rophic Pap smears in postmenopausal women and to study their clinical signi ficance. STUDY DESIGN: A retrospective study of 412 atrophic Pap smears from post-me nopausal women was done to detect the presence of Bbs. The smears from 24 c ases showing Bbs were further studied to evaluate the nature of the Bbs wit h special stains, immunohistochemistry and electron microscopy. RESULTS: Bbs showed a heterogeneous morphology, with variable numbers and s taining intensity. The diameter of Bbs was approximately equivalent to that of a parabasal/intermediate squamous cell. Special stains showed Bbs to be positive for periodic acid-Schiff and methyl green pyronin and negative fo r mucicarmine and calcium. Immunohistochemistry revealed Bbs to be positive for cytokeratin, epithelial membrane antigen and carcinoembryonic antigen and negative for vimentin and muscle-specific actin. Some Bbs had residual ghost nuclear shadows. Electron microscopy revealed cellular skeletons with residual tonofilaments enmeshed within a loose cytoskeleton matrix and nuc lei with variable degrees of degeneration. CONCLUSION Special stains, immunohistochemistry and electron microscopy ind icated that Bbs represent parabasal/intermediate squamous cells exhibiting various degree of degeneration. In general, Bbs appear to be of no clinical significance except as a source of potential diagnostic error.