Abnormal Pap Smears and the Human Papiloma Virus
Frederick R. Jelovsek MD
The human papillomavirus (HPV) has been identified as the most common culprit associated with abnormal Pap smears. Some strains of HPV are apparently more virulent than others and HPV subtypes 16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, 59 and 68 have been associated with severe grades of cervical dysplasia and invasive cancer of the cervix. DNA test is used to identify subtypes of HPV and up to now it has been more expensive and inconvenient to offer as routine testing. Theoretically, if all women with abnormal Pap smears could have HPV subtype testing then those associated with the more virulent strains would be the only ones requiring treatment.
Right now the rule-of-thumb in the U.S. is to follow women with ASCUS (atypical squamous changes of undetermined significance) and mild dysplasia (CIN I) with repeat Pap smears every 3-6 months. That is because most of them go away on their own as the woman's body mounts an immune response. Moderate or severe dysplasia changes are usually treated with procedures that destroy the affected cells along with normal tissue. It would be nice to know which women with ASCUS or mild dysplasia were going to get worse with time. Then they could be treated early. Also it would be nice to know which women with moderate or severe dysplasia could be followed with just repeat Pap smears rather than having to have a destructive procedure to the cervix that may affect future fertility.
With the advent of the thin Pap, there is fluid left over from the specimen that can be tested for HPV DNA without having the woman return for an additional visit and procedure to obtain a specimen -- Pap or biopsy. Thus if a Pap is abnormal, it can be immediately tested for worrisome HPV strains. A recent study looked at the practicality of this. Wright Jr. TC, et al.: Reflex human papillomavirus deoxyribonucleic testing in women with abnormal Papanicolaou smears. Am J Obstet Gynecol 1998; 178:962-6.
These authors studied 265 women with different grades of Pap smears and biopsies. They found that in patients who had ASCUS, the lowest grade of Pap abnormality, HPV DNA testing could identify 90% of those women who were likely to have a more severe lesion (high grade dysplasia) on actual biopsy. Unfortunately, with the higher grades of Pap abnormality, the testing was not sensitive or specific enough to be useful as to which women could be followed rather than biopsied.
While more studies have to be done in this area, our knowledge about abnormal Paps and HPV has advanced significantly in the last decade and if the thin Pap test becomes more widely used, we will see more studies about HPV association that will help us know in which instances to treat or not treat with greater precision.