Discussion:
This systematic review reported 15 studies totally involving 612
patients with LP treated with CO2 laser or KTP laser and
2120 surgeries, including 102 KTP cases from 5 studies and 510
CO2 cases from 10 studies separately. Both
CO2 and KTP groups were improved postoperatively in
clinical outcomes. Compared with the CO2 group, the KTP
group showed significantly better results in cure rate and had a lower
postoperative complication rate. To the best of our knowledge, this work
is the first study that systematically and comprehensively compares the
clinical outcomes of CO2 and KTP lasers for LP.
Although LP is a benign disease as mentioned above, it is frequently
associated with substantial morbidity and mortality4.
Therefore, balancing treatment goals (voice preservation and disease
regression and/or restoration) with the morbidity and cost of the
treatment is required and should be seriously considered before
treatments7. Recent studies have found that Human
papillomavirus (HPV, a DNA virus) is the cause of LP. Besides, pieces of
evidence suggested that more than 100 genotypes of HPV infecting
exist45–47. For instance,HPV-6 and HPV-11 result in
the low-risk and the most common LP; HPV-16 and HPV-18 play a high-risk
role but rarely happen48. According to clinical cases
observed, two categories are divided depending on onset age. Juvenile
onset RRP (JoRRP) represents the onset age of patients less than 12
years old, while adult-onset RRP (AoRRP) more than 12 years
old5,8. Most JoRRP is transmitted vertically during
pregnancy or acquired from a contaminated mother during delivering; as
for AoRRP, it is often sexually transmitted by oral
sex49. Besides, a trimodal distribution has been
pointed out that 7, 35, and 64 years old are the peaking onset
ages50. In spite of this, a bimodal distribution is
most acceptable by researchers5,49,51. Based on the
information, a serial of anti-viral drugs was investigated for LP,
including the HPV vaccine, Interferon, Cidofovir, Bevacizumab,
Celecoxib, and so forth5,52. For instance, the
meta-analysis of Rosenberg et al. found that the number of
surgeries/months was significantly reduced after long-term HPV
vaccination than before vaccination53. These adjuvant
treatments may benefit patients with LP treated with surgical excision
and more studies are needed to assess the effects of combination KTP
laser surgery with adjuvant therapies.
In this review, we found that both KTP and CO2 laser
groups demonstrated satisfactory outcomes for LP in the cure rate,
87.25% and 75.98% respectively. In addition, the cure rate of KTP
laser is significantly higher than that of CO2 laser,
which demonstrated the main therapeutic effect of KTP laser is superior.
Another evaluation indicator is recurrence rate, but we found there no
difference between the two groups for LP treatment (9.8% vs 10%,
p=0.2967). Moreover, the safety outcome-complication rate of the KTP
group is 2.32%, which is considerably lower than that of
CO2 laser (17.71%) (p<0.0001). Those findings strongly
support our hypothesis that KTP laser could yield comparatively better
outcomes than CO2 laser for LP.
Several reasons may explain why KTP laser was superior to
CO2 laser for LP according to literature. The
CO2 laser was firstly used in the 1960s and it quickly
gained popularity for LP14,18. Many therapeutic
options have been advocated for LP, such as microblade and PDL laser,
but surgical removal using CO2 laser remains the most
important single treatment choice4,54,55. Although the
10 600 nm wavelength of the CO2 laser is well absorbed
by water in biological tissue and is suitable for fine surgical cutting,
its application to remove laryngeal lesions is not without
risk56,57. Thermal injury, excessive resection, and
repeated surgeries may result in a loss of pliable vocal fold tissue,
fibrosis, and scar formation, which can significantly affect the quality
of voice and life34,58.
As for KTP laser, it has both the cutting function of
CO2 laser and the hemostatic effect of PDL laser, so its
application in laryngeal microsurgery has many advantages: (1) The
operation is significantly less destructive than the traditional
laryngeal laceration, without laryngeal laceration, and with less
tracheotomy ratio. In addition, KTP laser is more likely to preserve
postoperative laryngeal function, and the postoperative hospital stay
was short (less cost), requiring only 2 to 3 days44.
(2) The accuracy and precision of the operation were improved by using a
KTP laser. The tumor boundary can be clearly seen under the microscope,
and the level of incision can be distinguished so that the lesion can be
completely removed while minimizing collateral
damage59. (3) The fiber-based delivery of the KTP
laser with the technical advancement of distal-tip endoscopy enables
surgical procedures to be performed in-office settings under local
anesthesia, by which considerable time and medical expenses would be
saved31,35. (4) The KTP laser has a good hemostatic
effect and allows the surgery to be performed in a bloodless manner.
Especially in children with laryngeal papilloma invading the
supraglottis, the tumor has a rich blood supply. Under this condition,
the KTP laser can be applied to its advantage, resulting in a clear
field and a well-defined cut, reducing collateral
damage5,53.
This study had several limitations. Firstly, the available studies or
data about KTP laser used for LP were very limited (102 patients).
Whereas the cases number achieved the minimal sample number after
conducting a sample size estimation (58 in each group). Secondly, much
data collected by different studies are not consistent between KTP and
CO2 groups. For example,
HPV positive rate, remission rate,
and clearance rate for LP were always presented in the
CO2 group but rarely appeared in the KTP
group1,40, which made it impossible to compare those
parameters and may potentially influence the results of this study. We
recommend that future studies should report those data for patients with
LP as possible. In addition, the age difference (before surgery) between
CO2 group and KTP group should be noted. But we believe
due to most studies in CO2 group did not report the
detail age of patients (419/510 patients), the data of age from the two
groups was not representative and the difference should not be a serious
problem. Thirdly, high-quality comparative evidence is significantly
insufficient as most studies included were at level D. The MINORS scores
of these studies averaged 13.1 and 13.6 in the CO2 group
and KTP group, respectively, demonstrated the fair quality of evidence.
Future research in the form of standard-evaluation prospective
multicenter randomized controlled studies is required.