Atrophic cells with enlarged dark nuclei are seen in a background of inflammatory cells, intermediate and parabasal cells.
Note the dark smudgy chromatin of the atrophic cells. These cells may be erroneously interpreted as LGSIL.
DeMay suggests that you compare the quality of the chromatin with surrounding normal parabasal or intermediate cells. If the nuclei are similar, the cells may be atrophic. If the nuclei are distinctly coarser, darker and crisper, consider dysplasia.
Another image of atrophic cells with increased N/C ratios.
In this case, atrophic cells are admixed with LGSIL. Note that the clearly dysplastic cell contains coarser chromatin and irregular nuclear contours.
Squamous intraepithelial lesions must be distinguished from the various 'atypias' including radiation atypia, reactive/inflammatory atypia, reparative atypia and of course, atypia of atrophy. It is often challenging to separate these atypias from dysplasia as there are many shared features including pleomorphism, hyperchromatism, cytoplasmic vacuolization, multinucleation, etc. However, experience and clinical history (very important) will guide you through this gauntlet.
Atypia of atrophy often occurs in post-menopausal women or in women on Depo-Provera. Atrophic cells can mimic dysplasia in that the nuclei can be pleomorphic, hyperchromatic with increased N/C ratios. Atrophic nuclei, however, are more smudgy whereas dysplastic nuclei are crisper. Furthermore, dysplastic nuclei differ from one another in size and quality of chromatin. Atrophic nuclei are fairly uniform and pleomorphism, although present, is minimal (DeMay).
Ki-67 staining should also be valuable since atrophic epithelium is not mitotically active. A word of caution, however, in that the lack of Ki-67 staining does not definitively rule out dysplasia as older women may have dyplastic lesions with low mitotic activity.1,2
If it is difficult to differentiate between atrophy and dysplasia, the clinician could administer estrogen, which would mature the epithelium. A repeat Pap smear can be performed to see if the atrophic cells have been replaced by normal squamous epithelium.
1 Nucci MR, Oliva Esther. Gynecologic Pathology: Foundations in Diagnostic Pathology. Philadelphia, PA: Elsevier: 2009: 152.
2 DeMay RM. The Art and Science of Cytopathology. Chicago, IL: ASCP Press; 1996; 116-7.