DNA Viruses: Papovaviruses
Human papovaviruses, also called papillomaviruses (HPV), are small, nonenveloped, double-stranded DNA viruses with an icosahedral capsid. Persistent viral infection of susceptible epithelial cells induces cellular proliferation and can lead to malignant transformation. Papillomavirus proteins can induce transformation of the cell and loss of senescence. HPV subtypes 6 and 11 are maintained in a latent state within basal epithelial cells as circular episomes with very limited viral gene transcription and low copy number. Early viral gene products stimulate cell growth and lead to a skin wart or a conjunctival papilloma. As HPV-containing basal epithelial cells mature and differentiate into superficial epithelial cells, they become permissive for complete viral gene expression and produce infectious virus. Neoplastic transformation due to HPV 6 or 11 is very rare. In contrast, HPV 16 and 18 stereotypically integrate their viral genome into host chromosomal DNA, and this in turn is associated with malignant transformation and squamous cell carcinoma. Recently implemented immunization strategies specifically targeted against HPV oncogenes may result in a decreased incidence of these tumors in the future.
Verrucae and papillomas are caused by papillomavirus infection of the skin and conjunctival epithelium (Fig 9-23). Papillomavirus-associated conjunctival intraepithelial neoplasia and squamous cell carcinoma share many histologic features with similar lesions in the uterine cervix. Treatment of conjunctival papillomas can be frustrating. Medical therapeutic options include systemic cimetidine 30 mg/kg/day in 3 divided doses for 3 months or more, or topical interferon alfa-2b three times a day for the same treatment period. “No-touch” surgical excision with adjuvant cryotherapy is the preferred surgical option and is followed by administration of oral cimetidine or topical interferon, as described above. Seeding of adjacent conjunctiva may occur following surgical excision, resulting in spread. Another neoplasm, Kaposi sarcoma of the skin or conjunctiva, is associated with infection with human herpesvirus 8, not HPV. These entities are discussed in greater detail in Chapter 12.
Figure 9-23 Conjunctival papillomas.
(Courtesy of Elmer Y. Tu, MD.)
Kaliki S, Arepalli S, Shields CL, et al. Conjunctival papilloma: features and outcomes based on age at initial examination. JAMA Ophthalmol. 2013;131(5):585–593.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.