Objective: To estimate the prevalence of anal intraepithelial neoplasia in heterosexual women with genital intraepithelial neoplasia, and to compare anal cytology with colposcopy for their effectiveness in anal intraepithelial neoplasia screening.
Methods: Women with confirmed intraepithelial neoplasia on the cervix, vagina, or vulva were referred for gynecologic oncology care. All patients underwent anal cytology and high-resolution anoscopy. Any lesion detected on anoscopy was biopsied. Wilson score method was used to estimate 95% confidence interval for prevalence. McNemar's test compared the two screening methods.
Results: Women with average age of 39.6 years (range 14 to 83 years) underwent anal cytology and anoscopy (N=205). Of the 205 patients with genital intraepithelial neoplasia, 25 patients (12.2%) had biopsy-proven anal intraepithelial neoplasia. Twelve patients (5.9%) had abnormal anal cytology (nine with atypical squamous cells of undetermined significance [ASC-US], three with low-grade squamous intraepithelial lesions [LSIL]). None of the nine patients with anal ASC-US had biopsy-proven anal intraepithelial neoplasia. Of the three patients with anal LSIL, two had anal intraepithelial neoplasia II and one had condyloma on biopsy. However, 78 patients (38%) had abnormal anoscopy findings that resulted in 25 biopsy-proven anal intraepithelial neoplasias (8 anal intraepithelial neoplasia I, 5 anal intraepithelial neoplasia II, 12 anal intraepithelial neoplasia III)), condylomas (n=11), and hyperkeratosis (n=8). Anoscopy identified 32% (25 patients) with anal intraepithelial neoplasia out of 78 abnormal anoscopic examinations. In diagnosing anal intraepithelial neoplasia, anoscopy has 100% sensitivity and 71% specificity; anal cytology has 8% sensitivity and 94% specificity.
Conclusion: Patients with cervical, vulvar, and vaginal intraepithelial neoplasia have 12.2% prevalence of anal intraepithelial neoplasia and should be screened with high-resolution anoscopy. In anal intraepithelial neoplasia screening, anoscopy is more sensitive but less specific than anal cytology.