Section: Colorectal Sub-section: Proctology Curriculum: Curriculum, page 23
Definition
- Cause by Human papillomavirus
- Flat dysplastic change in the squamous mucosa and skin of the anal canal and perianus.
- LSIL - AIN1
- Dysplasia in the lower third of the epithelium
- HSIL - AIN2/3
- Characterised by the expression of HPV genes E6 and E7.
- AIN2 2/3 dysplasia of the lower
- AIN 3 full thickness dysplasia
Risks
- MSM
- HIV
- Immunocompromised
Pathophysiology
- Infection of the keratinocytes
- Deregulates cellular protein expression
- Disorganised proliferation of the basal epithelial cell layer
- Progressively more dysplastic cells
- Ultimately leads to invasive cancer
Clinical
- Usually asymptomatic
- Itching
- Pain
Investigations
High-resolution anoscopy (HRA)
- Considered the gold standard
- 5% aqueous acetic acid is used through an ordinary proctoscope with high-resolution real-time high-quality magnification by colposcope up to 30 times.
- Regions of active HPV mucosal infection turn cloudy white (acetowhite)
Progression
-
LSIL doesn’t appear to progress to HSIL
- Associated with “low risk” HPV types
- May herald HPV infection with other subtypes (that lead to HSIL and SCC)
-
HSIL can progress to SCC
- Higher in immunocompromised
- Significant number also “cleared” of ASIL
Treatment
LSIL – do not require treatment other than surveillance
HSIL – should be considered for treatment
- Excision - not typically done anymore
- Ablation
- Topical treatments
The ANCHOR study showed treatment of HSIL reduced the rate of anal SCC https://www.nejm.org/doi/full/10.1056/NEJMoa2201048