How To: Does Intralesional Steroid Injection Effectively Mitigate Vocal Fold Scarring in a Rabbit Model?

INTRODUCTION

The increasing prevalence of professional voice users has led to a corresponding increase in voice-related issues, notably vocal cord polyps. Laryngomicrosurgery (LMS) is a common treatment for these conditions, often employing fiber optic lasers such as potassium-titanyl-phosphate (KTP) and pulse dye laser (PDL) in outpatient departments (OPDs). The use of lasers in these procedures can damage the vocal folds, however, leading to scarring.

In vocal fold scars, abnormal collagen levels increase, whereas those of elastin and hyaluronic acid decrease, leading to compromised vocal fold stiffness and viscosity due to the disorganization of the structure of the lamina propria. Various treatments are available for vocal fold scarring, including injections of autologous fat, collagen, or corticosteroids; scar excision; topical mitomycin-C application; and vascular stripping, but their effectiveness is limited. Therefore, the prevention of scarring becomes a crucial focus.

Steroid injections, known for their potent anti-inflammatory effects, are commonly used after laryngeal surgery, but conclusive evidence of their effectiveness in preventing scarring is lacking. Therefore, the primary objective of our study was to determine the effect of steroid injections in preventing vocal fold scarring. The secondary objective was to evaluate the differences in the preventive effects on vocal fold scarring based on the type of steroid used. Accordingly, the independent variables were the presence of steroid injection and the type of steroid injected, whereas the dependent variables were changes in the transcriptional, histological, and functional levels of vocal fold scars in a rabbit model.

MATERIALS AND METHODS

Ethics Statement: All animal experiments received prior approval from the Institutional Animal Care and Use Committee of Soonchunhyang University Bucheon Hospital. Care for all rabbits was in accordance with the Guidelines on the Care and Use of Laboratory Animals of Soonchunhyang University College of Medicine (IRB No. SCHBCA2022–09).

Animal Model of Vocal Fold Scar and Steroid Injection

The study involved 42 male New Zealand white rabbits, aged six months and weighing 2.5-3.0 kg. Each rabbit underwent bilateral vocal fold scar surgery using a 532-nm diode laser. Then, 28 were randomized into groups to receive an additional corticosteroid (dexamethasone or triamcinolone) injection into the superficial layer of the lamina propria, with 14 animals per group. The remaining 14 rabbits, which underwent the same surgery without additional treatment, served as negative controls. Ten rabbits from each group were subjected to high-speed vibration testing and subsequent histological analysis. Four rabbits from each group were used for real-time polymerase chain reaction (PCR) to assess the expression levels of extracellular matrix (ECM) genes (Fig. 1).