Delayed but Long-term Resolution of Nevus of Ota After Cessation of Picosecond 755-nm Alexandrite Laser Treatment Moore, Angela, MD1,2,3,4; Nguyen, An, B.S4; Nguyen, Ly4, Michael Thornton, D.O.5 1Arlington Center for Dermatology, Arlington, TX; 2Arlington Research Center, Arlington, TX; 3Baylor University Medical Center, Dallas, TX;4Texas Christian University Anne Burnett Marion School of Medicine, Fort Worth, TX; 5Mansfield Cosmetic Surgery Center, Mansfield, TX

Key words: Nevus of Ota, hyperpigmentation, picosecond, alexandrite Corresponding author: Angela Yen Moore, MD Arlington Center for Dermatology 711 East Lamar Blvd., Suite 200, Arlington, Texas 76011 817-795-7546 phone 817-385-7568 fax acderm@acderm.com Word Count: 399 References: 9 Figure/Tables: 2 Funding: None Conflicts of interest: None

Consent: Consent for the publication of all patient photographs and medical information was provided by the authors at the time of article submission to the journal stating that all patients gave consent for their photographs and medical information to be published in print and online and with the understanding that this information may be publicly available.

Introduction Nevus of Ota presents as unilateral benign melanosis in the distribution of the trigeminal nerve, with increased risk of uveal melanoma and glaucoma¹. Since the advent of selective photothermolysis, Q-switched nanosecond lasers have been reported for treatment of dermal pigmented lesions⁷. Two prospective, randomized, split-lesion, controlled studies have concluded that picosecond lasers were more effective³. In these cases, treatment until clinical clearance was performed. We would like to report a case of nevus of Ota that was treated with a picosecond 755 nm Alexandrite laser displaying continued marked resolution after cessation of treatment, without recurrence for 5 years. Case Report A thirty-five-year-old Asian woman with a bluish-gray confluent pigmentation along the right V1 distribution presented for diagnosis and treatment. Six treatments with a 750-picosecond pulse duration 755-nm alexandrite laser were performed, with one session every 2 weeks over 10 weeks. Patient was instructed to use topical sunscreen with zinc oxide >11% and topical healing creams. The patient experienced 8/10 pain with the first treatment session that decreased to 2/10 with pre-application of topical anesthetic cream (benzocaine 20%/ lidocaine 4%/ tetracaine 1%) 30 minutes prior to each session. Local skin reactions included temporary erythema and mild transient hyperpigmentation but no hypopigmentation. The hyperpigmentation decreased progressively but with persistent central blue-black pigmentation.Treatment was terminated when the patient moved away. When the patient was seen 1 year later, the nevus of Ota had resolved completely and the patient reported continued improvement for the 6 months after the last laser session until full clearance. The only continued maintenance treatment was usage of topical sunscreen with 11% zinc oxide. Bibliography Picosecond lasers rely on photomechanical effects rather than photothermal. In contrast to nanosecond-domain Q-switched lasers, picosecond-domain lasers have a pulse width shorter than the stress relaxation time of dermal dendritic melanocytes and melanophages⁵. Mechanical stress generated within a very short period of time results in stress lock-in causing rise in pressure and fracture of the target particle and photoacoustic destruction of the particle, with a minimal photothermal component. The bursts of energy have been speculated to break down the melanin granules and melanophages, with clinical resolution occurring as macrophages carry away the fractured particles even after cessation of laser sessions⁴. This case report of delayed but persistent clinical resolution of a nevus of Ota validates theories on how picosecond lasers achieve clinical response through photomechanical effects followed by immunologic response.

References Agarwal P, Patel BC. Nevus of Ota and Ito. Updated 2023 Jul 10. In: StatPearls Internet. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK560574/ Chesnut, Cameron MD; Diehl, Joseph MD; Lask, Gary MD. Treatment of Nevus of Ota With a Picosecond 755-nm Alexandrite Laser. Dermatologic Surgery 41(4):p 508-510, April 2015. | DOI: 10.1097/DSS.0000000000000326 Ge Y, Yang Y, Guo L, Zhang M, Wu Q, Zeng R, Rong H, Jia G, Shi H, Fang J, Lin T. Comparison of a picosecond alexandrite laser versus a Q-switched alexandrite laser for the treatment of nevus of Ota: A randomized, split-lesion, controlled trial. J Am Acad Dermatol. 2020 Aug;83(2):397-403. doi: 10.1016/j.jaad.2019.03.016. Epub 2019 Mar 16. PMID: 30885760. Imagawa, K., Kono, T., Hanai, U. et al. Prospective comparison study of a 550 picosecond 755 nm laser vs a 50 ns 755 nm laser in the treatment of nevus of Ota. Lasers Med Sci 38, 55 (2023). https://doi.org/10.1007/s10103-023-03721-5 Kasai K. Picosecond Laser Treatment for Tattoos and Benign Cutaneous Pigmented Lesions (Secondary publication). Laser Ther. 2017 Dec 31;26(4):274-281. doi: 10.5978/islsm.17-RE-02. PMID: 29434427; PMCID: PMC5801452. Luo B, Kang L, Lu J. Successful and quick treatment of nevus of Ota with 755nm picosecond laser in Chinese. J Cosmet Laser Ther. 2020 Feb 17;22(2):93-95. doi: 10.1080/14764172.2020.1740274. Epub 2020 Mar 11. PMID: 32160794. Wong THS. Picosecond Laser Treatment for Acquired Bilateral Nevus of Ota–like Macules. JAMA Dermatol. 2018;154(10):1226–1228. doi:10.1001/jamadermatol.2018.2671 Yang H, Guo L, Jia G, Gong X, Wu Q, Zeng R, Zhang M, Ding H, Fang F, Zheng H, Liu X, Ge Y, Yang Y, Lin T. Treatment of nevus of Ota with 1064 nm picosecond Nd:YAG laser: A retrospective study. Dermatol Ther. 2021; 34(6):e15152. doi: 10.1111/dth.15152. Epub 2021 Oct 14. PMID: 34609042. Yu W, Zhu J, Yu W, Lyu D, Lin X, Zhang Z. A split-face, single-blinded, randomized controlled comparison of alexandrite 755-nm picosecond laser versus alexandrite 755-nm nanosecond laser in the treatment of acquired bilateral nevus of Ota-like macules. JAAD. 2018; 79(3): 479-486. doi: 10.1016