Age of child, more than HPV type, is associated with clinical course in recurrent respiratory papillomatosis

Abstract

Background: RRP is a devastating disease in which papillomas in the airway cause hoarseness and breathing difficulty. The disease is caused by human papillomavirus (HPV) 6 or 11 and is very variable. Patients undergo multiple surgeries to maintain a patent airway and in order to communicate vocally. Several small studies have been published in which most have noted that HPV 11 is associated with a more aggressive course.

Methodology/principal findings: Papilloma biopsies were taken from patients undergoing surgical treatment of RRP and were subjected to HPV typing. 118 patients with juvenile-onset RRP with at least 1 year of clinical data and infected with a single HPV type were analyzed. HPV 11 was encountered in 40% of the patients. By our definition, most of the patients in the sample (81%) had run an aggressive course. The odds of a patient with HPV 11 running an aggressive course were 3.9 times higher than that of patients with HPV 6 (Fisher's exact p = 0.017). However, clinical course was more closely associated with age of the patient (at diagnosis and at the time of the current surgery) than with HPV type. Patients with HPV 11 were diagnosed at a younger age (2.4y) than were those with HPV 6 (3.4y) (p = 0.014). Both by multiple linear regression and by multiple logistic regression HPV type was only weakly associated with metrics of disease course when simultaneously accounting for age. CONCLUSIONS/SIGNIFICANCE ABSTRACT: The course of RRP is variable and a quarter of the variability can be accounted for by the age of the patient. HPV 11 is more closely associated with a younger age at diagnosis than it is associated with an aggressive clinical course. These data suggest that there are factors other than HPV type and age of the patient that determine disease course.

Figure 1. Papilloma biopsies were taken at the time of enrollment and subjected to HPV typing.

For those cases where the enrollment surgery was not their first surgery, the interval in days since the last surgery was recorded. Variables were transformed so that they would comply with a Gaussian distribution. The natural log of the number of days since the last surgery are depicted on the y axis. The left panel depicts a linear regression against the square root of the age at the time of enrollment. The model predicts that a 4 year old last had surgery 69 days (2.3 months) ago and a 9 year old last had surgery 113 days (3.7 months) but only 20% of the variability is accounted for by this model. The right panel depicts a boxplot of the same data but clustered by HPV type. The geometric mean of the number of days since the last surgery was 119 days (3.9 months) for those with HPV 6 and a similar 97 days (3.2 months) for those with HPV 11. The t-test p-value was 0.25.

Figure 2. Agarose gel electrophoresis of HPV 6 and 11 specific PCR fragments.

The first 2 lanes after the ladder (both labeled “1”) represent the wells for HPV 6 positive control clone for the TS-PCR using either primer pair 6930–6932 (designed to be specific for HPV 6) or 6931–6933 (designed to be specific for HPV 11). The same pattern applies to the remaining lane couplets. The couplet labeled “2” represents HPV 11 positive control clone. Couplets 3–8 are RRP specimens and couplet 9 is the PCR negative control. In this gel we see that that laryngeal DNA used in couplet 3 contained only HPV 11 and the remainder contained only HPV 6.

Figure 3. HPV 6 and 11 genotyping by restriction fragment length polymorphism.

BstN I enzyme is a single cutter for the 929 bp HPV6 and 11 consensus PCR fragment. HPV6 possesses the enzyme recognition site thus the digestion yields two fragments of size 526 and 403 bp while HPV11 does not. Lanes 1 and 2 are HPV 6 and 11 positive controls. Lanes 3–13 are RRP patients.