Prevalence of anal squamous intraepithelial lesions in HIV-positive and HIV-negative men who have sex with men in Thailand.

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1598 Background: Men who have sex with men (MSM) are at increased risk for high-grade squamous intraepithelial lesions (SIL), the putative precursor to anal cancer. Since 2006, the Thai Red Cross AIDS Research Centre (TRCARC) in Bangkok has offered anal cytology screening to MSM clients. Methods: Demographics, CD4+ T cell count, viral load, and anal cytologic (pap smear) and histologic (biopsy) specimens were collected as available from MSM who attended the TRCARC between February 1, 2008 and November 30, 2009. Chi-square analysis and Student's t-test were used to evaluate risk factors and SIL prevalence. Results: A total of 912 Thai MSM received anal cytology screening. Mean age was 31 years, and 65.8% (n = 600) were HIV-positive. Prevalence of abnormal anal cytology was 18.4%. HIV–positive MSM had higher prevalence of SIL than HIV-negative MSM (23.7% versus 8.3%, p < 0.001). Anal condyloma by clinical examination was detected in 11.2% of HIV-positive and 9.7% of HIV-negative patients (p = 0.496). Among HIV-positive MSM, 15.3% had atypical cells of undetermined significance (ASC- US), 8.2% had low-grade SIL (LSIL), and 0.2% had high-grade SIL (HSIL). Those with SIL were younger (29.9 vs. 32.2 years, p = 0.002) and had lower CD4+ T cell counts (283.9 vs. 372.2 cells/mm3, p < 0.001) than those with normal cytology. Among HIV-negative MSM, the prevalence of ASC-US, LSIL, and HSIL were 5.8%, 1.9%, and 0.6%. In follow-up, 91 MSM underwent a second pap smear, of these 11.0% progressed in cytologic grade, 28.6% regressed, and 60.4% were unchanged. The proportion of MSM with regression or progression of cytology did not differ by HIV infection (p = 0.905). Thirty-six men with SIL had high resolution anoscopy, and 35 underwent biopsy. Histology results were normal (14.3%), or were consistent with HPV infection (17.1%), AIN I (14.3%), AIN II (8.6%), AIN III (8.6%) and condyloma (31.4%). Conclusions: Prevalence of SIL is high among MSM in Thailand. Abnormal cytology was associated with lower CD4+ T-cell count and younger age among HIV-positive MSM. Histology confirmed high prevalence of AIN but did not correspond to pap cytology. Improved detection methods for pre-cancerous anal lesions are needed. No significant financial relationships to disclose.