Dermatology: Practical and Conceptual Image Letter | Dermatol Pract Concept. 2023;13(4):e2023222 1 Monkeypox Infection Mimicking Oral Primary Syphilis Jorge Naharro-Rodríguez1, Gerald Selda-Enríquez1, Emilio García-Mouronte1, Luis Alfonso Pérez-González1, Ileana Teresa-Dianzo2, Pablo Fernández-González1 1 Dermatology Department, Ramón y Cajal University Hospital, IRYCIS, Madrid, Spain 2 Microbiology Department, Ramón y Cajal University Hospital, IRYCIS, Madrid, Spain Citation: Naharro-Rodríguez J, Selda-Enríquez G, García-Mouronte E, Pérez-González LA, Teresa-Dianzo I, Fernández-González P. Monkeypox Infection Mimicking Oral Primary Syphilis. Dermatol Pract Concept. 2023;13(4):e2023222. DOI: https:// doi.org/10.5826/dpc.1304a222 Accepted: April 16, 2023; Published: October 2023 Copyright: ©2023 Naharro-Rodríguez et al. This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial License (BY-NC-4.0), https://creativecommons.org/licenses/by-nc/4.0/, which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original authors and source are credited. Funding: None. Competing Interests: None. Authorship: All authors have contributed significantly to this publication. Corresponding Author: Jorge Naharro-Rodríguez, Dermatology Department, Ramon y Cajal University Hospital IRYCIS. Colmenar Viejo km 9.100, 28034 Madrid, Spain. Phone no.: +34627654405; FAX +34913062268. Email: jorgenrmed@gmail.com Case Presentation A 32-year-old HIV-positive man who has sex with men (MSM) presented to emergency department with a two-day history of a firm, painless solitary chancre-like nodule on lower lip (Figure 1A), associated with tender bilateral cervi- cal lymphadenopathy in the absence of other systemic symp- toms. The patient reported practicing unprotected receptive oral sex 3 weeks before. He re-consulted 2 days later due to the onset of tenderness and swelling of the lower lip with as- sociated fever. Physical examination then revealed lesion en- largement and ulceration as well as development of clustered satellite papules on labial mucosa (Figure 1B). A polymerase chain reaction (PCR) of swabs obtained from the ulcer and pharynx were positive for monkeypox virus (MPXV). Per- formed venereal disease research laboratory (VDRL) and Treponema pallidum particle agglutination (TPPA) tests were repeatedly negative. Bacterial cultures obtained from the ulcer, pharynx and rectal swabs were all sterile. Teaching Point Because of shared risk factors and similar incubation period, it is reasonable to include MPXV infection in the differential diagnosis of primary syphilis in patients at risk presenting with a solitary lesion in the oral or genital regions. This has already been suggested in two recently published case re- ports [1,2]. 2 Image Letter | Dermatol Pract Concept. 2023;13(4):e2023222 In this scenario, it may be useful looking out for the pres- ence of pain and edema in the involved region, development of satellite papules as shown in this case or the appearance of painful lymphadenopathy, all of them pointing to the di- agnosis of MPVX infection, with PCR being the diagnostic test of choice. The patient in this manuscript has given written informed consent to publication of his case details. References 1. Turco M, Mancuso FR, Pisano L. A monkeypox virus infection mim- icking primary syphilis. Br J Dermatol. 2022;187(6):e194-e195. DOI:10.1111/bjd.21847. PMID: 36005947. 2. Ramoni S, Maronese CA, Morini N, et al. Syphilis and mon- keypox co-infection: Coincidence, synergy or asymptomatic car- riage? Travel Med Infect Dis. 2022;50:102447. DOI:10.1016/j .tmaid.2022.102447. PMID: 36067937; PMCID: PMC9629038. Figure 1. (A, B) Solitary, firm, chancre-like painless nodule on the lower lip (A), subsequent physical examination revealed enlargement and ulceration of the lesion as well as development of clustered satellite papules on labial mucosa (B).