A teenaged girl with flat-topped papules

A 15-year-old girl presented with multiple, small, flat-topped, minimally scaly papules scattered over both forearms, some arranged in a linear pattern extending from the elbows to the wrists, that had been present for several months (Figure). She denied any associated pruritus, pain, color changes, or bleeding. Her medical history was unremarkable for immunodeficiency, atopic dermatitis, or other skin conditions. 

On examination, the patient appeared well nourished and in no distress. Vital signs were within normal limits. There were numerous 1- to 3-mm, flat-topped, minimally scaly, smooth, flesh-colored to lightly hyperpigmented papules distributed bilaterally over her forearms. The lesions were confined to the upper extremities, sparing the palmar surfaces of the hands. The remainder of the physical exam was unremarkable. 

Diagnosis

Disseminated flat warts (verruca plana)

Etiology/clinical findings

Flat warts (verruca plana) are benign epithelial proliferations caused by the human papillomavirus (HPV) types 3 and 10.¹ They account for fewer than 5% of all cutaneous warts and predominantly affect children, adolescents, and young adults.^2,3

Disseminated flat warts are characterized by many lesions distributed over an anatomical area.⁴ The pseudo-Koebner phenomenon, defined as new wart formation along lines of skin trauma, is a hallmark feature and reflects autoinoculation of HPV into areas of epidermal disruption, explaining the linear clustering sometimes observed.^5,6 HPV is transmitted by direct skin-to-skin contact or fomites, with epidermal disruption permitting viral entry.⁷

Flat warts are generally transmitted through close contact and are self-limited in immunocompetent individuals, with spontaneous regression occurring over weeks to years as the immune system mounts a cell-mediated response against HPV-infected keratinocytes.^8,9 However, disseminated cases may be more recalcitrant and may require cosmetic treatments if emotionally distressing for the patient.¹⁰ (Table)^11-15

Management

In immunocompetent patients, watchful waiting is a reasonable management option, as verruca plana may spontaneously resolve over time.¹⁶

For disseminated or cosmetically concerning lesions, active treatment can be considered. First-line therapies include topical salicylic acid and topical retinoids, which promote gradual lesion clearance through keratolysis and modulation of epidermal turnover.^17,18

For recalcitrant or widespread warts, intralesional immunotherapy with Candida antigen or other recall antigens has demonstrated efficacy by stimulating a systemic cell-mediated immune response, which may also result in lesion clearance.¹⁹

Regardless of the modality chosen, patients and families should be counseled that complete clearance may take weeks to months and that recurrence is possible.²⁰

References

1. Usami T, Ohsawa I, Suga Y, Mitsuishi T. Human papillomavirus type 94-associated flat warts and review of reported cases. J Dermatol. 2024;51(1):95-97. doi:10.1111/1346-8138.16962

2. Bristow I. Paediatric cutaneous warts and verrucae: an update. Int J Environ Res Public Health. 2022;19(24):16400. doi:10.3390/ijerph192416400

3. Al Rudaisat M, Cheng H. Dermoscopy features of cutaneous warts. Int J Gen Med. 2021;14:9903-9912. doi:10.2147/IJGM.S335276

4. Leiding JW, Holland SM. Warts and all: human papillomavirus in primary immunodeficiencies. J Allergy Clin Immunol. 2012;130(5):1030-1048. doi:10.1016/j.jaci.2012.07.049

5. Zhang X, Lei L, Jiang L, et al. Characteristics and pathogenesis of Koebner phenomenon. Exp Dermatol. 2023;32(4):310-323. doi:10.1111/exd.14709

6. Camargo CM, Brotas AM, Ramos-e-Silva M, Carneiro S. Isomorphic phenomenon of Koebner: facts and controversies. Clin Dermatol. 2013;31(6):741-749. doi:10.1016/j.clindermatol.2013.05.012

7. Grimes RM, Benjamins LJ, Williams KL. Counseling about the HPV vaccine: desexualize, educate, and advocate. J Pediatr Adolesc Gynecol. 2013;26(4):243-248. doi:10.1016/j.jpag.2013.04.002

8. Oden P, Johnson SM. The current landscape of treatment of warts. J Drugs Dermatol. 2025;24(12):1208-1214. doi:10.36849/JDD.9099

9. Nordentoft EL, Waldorf FB. Vorter på hænder og fødder er oftest selvlimiterende. Abstract in English. Ugeskr Laeger. 2013;175(22):1559-1561.

10. Oren-Shabtai M, Snast I, Noyman Y, et al. Topical and systemic retinoids for the treatment of cutaneous viral warts: a systematic review and meta-analysis. Dermatol Ther. 2021;34(1):e14637. doi:10.1111/dth.14637

11. Boch K, Langan EA, Kridin K, Zillikens D, Ludwig RJ, Bieber K. Lichen planus. Front Med (Lausanne). 2021;8:737813. doi:10.3389/fmed.2021.737813

12. Yang K, Lau WC, Lau CB, Pan CX, Kassamali B, Nambudiri VE. Clinicopathologic features of lichen nitidus: a multicenter cohort. Int J Dermatol. 2023;62(4):e261-e263. doi:10.1111/ijd.16382

13. Chen X, Anstey AV, Bugert JJ. Molluscum contagiosum virus infection. Lancet Infect Dis. 2013;13(10):877-888. doi:10.1016/S1473-3099(13)70109-9

14. Peeling RW, Mabey D, Chen XS, Garcia PJ. Syphilis. Lancet. 2023;402(10398):336-346. doi:10.1016/S0140-6736(22)02348-0

15. Chevalier FJ, Bacon O, Johnson KA, Cohen SE. Syphilis: a review. JAMA. 2025;334(21):1927-1940. doi:10.1001/jama.2025.17362

16. Concha R M. Diagnóstico y terapia del virus papiloma humano. Article in Spanish. Rev Chilena Infectol. 2007;24(3):209-214. doi:10.4067/s0716-10182007000300006

17. Ali KA, Abu-Raghif AR, Ridha-Salman H. Evaluation of common topical therapeutic agents of plane warts. Arch Dermatol Res. 2025;317(1):246. doi:10.1007/s00403-024-03789-1

18. Liu Z, Ai J, Zhu Z, et al. Chemical peeling with 35% glycolic acid for the treatment of disseminated facial verruca plana: a randomized, split-face, evaluator-blinded trial. Dermatol Ther. 2022;35(8):e15594. doi:10.1111/dth.15594

19. Spach DH, Colven R. Resolution of recalcitrant hand warts in an HIV-infected patient treated with potent antiretroviral therapy. J Am Acad Dermatol. 1999;40(5 pt 2):818-821. doi:10.1053/jd.1999.v40.a95646

20. de Koning MNC, Quint KD, Bruggink SC, et al. High prevalence of cutaneous warts in elementary school children and the ubiquitous presence of wart-associated human papillomavirus on clinically normal skin. Br J Dermatol. 2015;172(1):196-201. doi:10.1111/bjd.13216