Introduction
A vocal fold polyp is a benign mid-membranous exophytic vocal fold lesion with a smooth surface. It is usually unilateral (but may be bilateral) and can be pedunculated or sessile.Reference Rosen, Gartner-Schmidt, Hathaway, Blacke Simpson, Postma and Courey1 Early theories of vocal fold polyp pathogenesis implicated phonotrauma as the inciting event, resulting in damage to the subepithelial capillary walls and protein-rich fluid exudation. Following this, organisation of the exudate may occur, leading to fibrovascular tissue formation. Alternatively, the exudate may undergo hyaline degeneration.Reference Kleinsasser2, Reference Kambic, Radsel, Zargi and Acko3
The role of mechanical stresses related to phonotrauma as an aetiological factor in vocal fold polyp development was corroborated by computational models. These have identified the most common site of pathogenesis as the centre of the free margin of the membranous vocal fold.Reference Gunter4 Phonotrauma is also reported to upregulate inflammatory biomarkers and repair mechanisms in the stressed vocal fold.Reference Li, Vodovotz, Kim, Mi, Hebda and Abbott5
Many patients with vocal fold polyps are cigarette smokers.Reference Martins, Defaveri, Domingues and de Albuquerque e Silva6 However, a PubMed and Medline search over the last 35 years identified no comparative study on the vocal fold polyp histopathology in smokers versus non-smokers. This study explored whether cigarette smoking has an impact on the histopathology of resected vocal fold polyps.
Materials and methods
Approval for this study was granted by the local ethics committee. The study period was one year, starting on 1 May 2013. Consecutive patients presenting with persistent hoarseness to the Otolaryngology Clinic at El-Sahel Teaching Hospital, Cairo, underwent video laryngoscopy to investigate laryngeal pathology. During the study period, 29 patients were clinically diagnosed with vocal fold polyps. A comprehensive medical history was taken for each patient, especially focusing on hoarseness duration and smoking status. All patients underwent microlaryngoscopy under general anaesthesia, during which polyp features and vocal fold appearance were documented. Polyps were completely excised at the base and the size was recorded. Polyps were fixed in 10 per cent formalin, embedded in paraffin, cut into 4 µm thick sections and stained with haematoxylin and eosin. Tissue sections were examined by light microscopy by a consultant pathologist with a special interest in laryngology. The pathologist was blinded to the smoking status of each patient.
The histological appearance of the epithelium, basement membrane and underlying lamina propria of the polyps was documented. The appearance of the epithelium was graded according to the Ljubljana classification into normal (atrophic), simple hyperplasia, dysplasia and atypia.Reference Gale, Zidar, Fischinger and Kambic7 The presence of superficial keratosis was noted. The basement membrane was classified as thin or thick. Lamina propria features were categorised as oedema, fibrosis, vascularisation, exudated red blood cells, hyalinisation and the presence of inflammatory cells, with each category being graded according to Hantzakos et al. as none, mild changes, moderate changes and marked changes.Reference Hantzakos, Remacle, Dikkers, Degols, Delos and Friedrich8
Results were expressed as the mean 00B1 standard deviation. The mean values of variables that differed between the two study groups (non-smokers versus smokers) were compared using unpaired t-tests. Categorical data were compared using chi-square tests. IBM SPSS Statistics software version 16.0 (Chicago, Illinois, USA) was used for data analysis. A p value less than or equal to 0.05 was considered statistically significant; a p value less than or equal to 0.01 was considered highly significant.
Results
The study group comprised 29 patients with 31 vocal fold polyps: 14 were non-smokers and 15 were smokers. Of the 14 non-smokers, 10 were female and 4 were male. All 15 smokers were male. Non-smokers ranged in age from 16 to 51 years (mean 35 years), and smokers ranged in age from 32 to 61 years (mean 44 years; p < 0.05). The average duration of hoarseness prior to presentation was longer in smokers than in non-smokers. For the non-smoking group, the right vocal fold was affected in nine patients and the left vocal fold in five patients. In the smoking group, 10 polyps were located on the left vocal fold and 3 were on the right; 2 patients had bilateral vocal fold polyps. The mean size of resected polyps was significantly greater in the smoking group than in the non-smoking group (p < 0.01). All 14 polyps from non-smokers and 17 polyps from smokers were histologically analysed, and various histopathological features in the epithelium and lamina propria were graded. The pathological features of polyps from non-smokers are shown in Table I and those of smokers in Table II. Significant differences in variables between the two groups are shown in Table III.
Table I Polyps pathology in non-smokers
–, none; +, mild changes; ++, moderate changes; +++, marked changes. Pt no = patient number; DoH = duration of hoarseness; Ker = keratinisation; NAtr = normal or atrophic; Hyper = hyperplasia; Dysp = dysplasia; Aty = atypia; BM= basement membrane; Vasc = vascularisation; Hya = hyalinisation; RBCs = exudated red blood cells; Inf = inflammatory cells; F = female; Lt = left; M = male; Rt = right
Table II Polyp pathology in smokers
–, none; +, mild changes; ++, moderate changes; +++, marked changes. Pt no = patient number; DoH = duration of hoarseness; Ker = keratinisation; Hya = hyalinisation; NAtr = normal or atrophic; RBCs = exudated red blood cells; Hyper = hyperplasia; Inf = inflammatory cells; Dysp = dysplasia; Aty = atypia; BM = basement membrane; Vasc = vascularisation; M= male; Lt = left; Rt = right; F = female
Table III Comparison of polyp features in smokers versus non-smokers
Data are expressed as mean ± standard deviation or number (%).*p < 0.05; **p < 0.01. RBCs = exudated red blood cells
Discussion
Vocal fold polyps are almost exclusively found in adult patients.Reference Martins, Defaveri, Domingues and de Albuquerque e Silva6 The youngest patient in the current study was 16 years old. There was a significant difference in mean patient age at presentation between groups: 35 years in the non-smoking group and 44 years in the smoking group (p < 0.05). In addition, hoarseness duration prior to presentation tended to be longer in the smoking group. These differences may be due to smokers attributing their hoarseness to simple chronic laryngitis, thereby delaying their presentation to the laryngologist.Reference Banjara, Mungutwar, Singh and Gupta9 Moreover, persistent squeezing of the polyps by sharp movements of the vocal folds during phonation and coughing may hamper repair mechanisms acting within polyp tissue, thus leading to recurrent capillary trauma and progression in polyp size.Reference Dikkers and Nikkels10 Indeed, in the current study, the mean polyp size was significantly larger in the smoking group than in the non-smoking group (p < 0.01).
In the current study, superficial epithelial keratinisation of polyps was more common in smokers than in non-smokers (p < 0.05). Chronic irritation by cigarette smoke is associated with abnormal keratin production and its accumulation in vocal fold epithelium.Reference Li-jing, Jun, Yang, Jing-ying, Wen and Quing-wen11 The presence of keratin on vocal fold epithelium indicates a phenotypic change because normal glottic epithelium is non-keratinising. The presence and degree of epithelial dysplasia is the most important prognostic factor driving conversion to malignancy in cases of superficial keratinisation.Reference Isenberg, Crozier and Dailey12
In this study, epithelial dysplasia with or without atypia was not observed in the non-smoking group, but was seen in 35 per cent of vocal fold polyps of smokers (p < 0.05). The major risk factor for laryngeal dysplasia development is cigarette smoking, although laryngopharyngeal acid and pepsin reflux may also be implicated.Reference Sadri, McMahon and Parker13 Cigarette smoking was reported to be associated with a higher incidence of reflux.Reference Smit, Copper, van Leeuwen, Schoots and Stanojcic14
In a comparative immunohistochemical study of benign vocal fold lesions, the basement membrane was found to be thinner in vocal fold polyps than in nodules.Reference Courey, Shohet, Scott and Ossoff15 In the present study, vocal fold polyps were significantly associated with thin basement membranes in smokers compared with non-smoker polyps (p < 0.05). It is possible that matrix metalloproteinases are upregulated in the inflammatory milieu present in membranous vocal folds exposed to cigarette smoke. These proteases may be responsible for type IV collagen digestion and basement membrane dissolution.Reference Hohberger, Wuertz, Xie, Griffin and Ondrey16 Basement membrane thinning is an important step in the progression from carcinoma in situ to microinvasive carcinoma.Reference Zhou, Xie, Zhou and Tao17
Pathophysiological factors related to the development and progression of vocal fold polyps are attributed to capillary breakage in Reinke's space resulting from mechanical stresses caused by voice overuse, misuse or abuse.Reference Johns18 Subsequent to capillary breakage, extravasation of blood or fibrin-rich oedematous fluid occurs. Ultimately, organisation processes develop, leading to neovascularisation and fibrous tissue deposition, and then to outpouching of Reinke's space.Reference Altman19 Ongoing shearing forces caused by abnormal phonation and coughing produce high levels of mechanical stress at the polyp base, leading to a self-perpetuating cycle of trauma and inflammation, with subsequent polyp growth.Reference Altman19–Reference Zhang and Jiang21
• A comparative histopathological study of vocal fold polyps in smokers versus non-smokers was performed
• There was a higher incidence of keratinisation, dysplasia and basement membrane thinning in smokers' polyps
• Smokers' polyps showed increased hyaline degeneration
Histopathological features of vocal fold polyps have been characterised as the presence of variable amounts of oedema, fibrosis, vascular ectasias, inflammatory cells and hyalinisation.Reference Hantzakos, Remacle, Dikkers, Degols, Delos and Friedrich8, Reference Wallis, Jackson-Menaldi, Holland and Giraldo22, Reference Cipriani, Martin, Corey, Portugal, Caballero and Lester23 These are consistent with the pathophysiological mechanism of vocal fold polyp development, as outlined above. The histopathological features observed in this study agree with those of previous studies. However, a highly significant increase in hyalinisation was observed in smokers' polyps compared with those of non-smokers (p < 0.01). Hyalinisation is a degenerative change in the fibrous collagen, probably in response to continuous tissue injury caused by cigarette smoke and to abnormal stresses on the polyp caused by phonotrauma and coughing.Reference Walter, Israel, Walter and Israel24
Conclusion
In the current study, a comparative analysis revealed that vocal fold polyps were significantly larger in cigarette smokers than in non-smokers. Histopathological evaluation revealed a higher incidence of keratinisation and dysplasia and a thinner basement membrane in polyps of smokers than in those of non-smokers. Moreover, the amount of hyaline degeneration was greater in the polyps of smokers than of non-smokers. These changes probably reflect the injurious effect of cigarette smoke on the epithelium and lamina propria of vocal fold polyps.
