Anal Intraepithelial Neoplasia Screening With Anal Pap Tests: Follow-up and Corresponding Histology

Anal cytology is used as a screening tool in the detection of precancerous anal squamous lesions. Follow-up clinical examination after abnormal anal cytology is recommended. The objective of this study was to determine how often abnormal cytology was followed by a clinical examination at our institution and how often cytology predicted histologic outcome.

A retrospective chart review was performed (2008-2018) on patients with anal cytology, demonstrating either low-grade or high-grade squamous intraepithelial lesion. Clinical examination within 1 y (digital rectal examination, anoscopy, or high-resolution anoscopy) was recorded. The probability of anal intraepithelial neoplasm on biopsy after dysplasia on cytology was calculated, and McNemar's test was used to determine if there was correspondence between cytology and histology.

A total of 327 anal cytology results demonstrated dysplasia (75% low grade and 25% high grade) in 182 patients. Seventy-five percent of dysplastic anal cytology were followed by clinical examination within 1 y, and 50% were biopsied. The probability of dysplasia on histology after dysplasia on cytology was 72% (95% confidence interval: 64%-78.5%). Twenty-eight percent of low-grade cytology results were upgraded to advanced disease (high-grade or invasive cancer) on histology. A low-grade cytology result was unable to preclude high-grade histology in our population.

There is room for improvement at our institution to consistently follow-up with clinical examination after abnormal anal cytology. Our data suggest this is especially important considering anal cytology is an imperfect predictor of histologic anal intraepithelial neoplasia and invasive disease. Clinical examination is a critical component of anal dysplasia screening and follow-up.