Patients had all presented a persistent hypertrophic scar at the neck region for more than 1 year after their thyroidectomy.

All patients received treatment using the same protocol with the same fractional ablative carbon dioxide laser (eCO2 PlusTM, manufactured by Lutronic, South Korea). Each patient was applied with Lidopin 5% cream (Panion & BF Biotech Inc.), which remained on the scar for 30 min for pain relief before each laser course. Later, the Lidopin 5% cream was gently removed using a normal saline-rinsed gauze, and the scar was treated with a fractional ablative carbon dioxide laser with two passes under a 10,600 nm wavelength, 120 mm spot size, pulse energy of 50 mJ, 30 W of power, and a density of 200. A topical steroid cream (clobetasol propionate, 0.05%) was evenly applied on the scar gently back and forth using a cotton swab immediately after the laser treatment. The patients underwent five full courses by the same doctor according to the same protocol, with each course given 4 weeks apart.

For each patient's self-assessment before the first treatment, we adopted the patient and observer scar assessment scale (POSAS)18, with a range of 1-10 for representing the severity of the itchiness, pain, color, softness, thickness, irregularity, and distorted appearance of the scar.

For each patient's self-assessment1 year after the first treatment, we adopted the patient and observer scar assessment scale (POSAS)18, with a range of 1-10 for representing the severity of the itchiness, pain, color, softness, thickness, irregularity, and distorted appearance of the scar.

Four doctors participated as observers of the clinical outcomes. One of the doctors carried out all treatments and evaluated seven parameters, namely, vascularity, pigmentation, thickness, relief, pliability, surface area, and overall opinion based on the POSAS using a scoring range of 1-10, from normal to worst conditions 1 year after the first treatment. The remaining three doctors acted as observers to evaluate the general appearances of the scars based on photographs captured by the same photographer with the same camera 1 year after the first treatment. They then rated the scar on a score of 1-10.