When a lip ulcer isn’t what it seems: Rare case of syphilis mistaken for mouth injury

Article by Dr. Ahmed Bakr Elazab Department of Dermatology, Andrology & STDs Faculty of Medicine, Suez University, Suez, Egypt, Ahmed.bakr.mohamed@gmail.com

The Case: A Painless Lip Sore That Defied Healing

A 32‑year‑old man presented with a persistent sore on his lower lip that had lasted three weeks and failed to respond to topical antibiotic cream. Strikingly, the ulcer caused no pain. He denied any history of lip biting, dental injury, or trauma. However, he reported oral‑genital sexual contact about 17 days before the sore appeared — a detail that proved crucial.

On examination, the lesion was well‑defined, firm, and measured 1.5 cm, with a clean base and slightly enlarged but non‑tender lymph nodes under the chin. Blood tests ruled out HIV and herpes, but syphilis serology (TPHA positive, VDRL titre 1:64) confirmed the diagnosis: primary syphilitic chancre of the lip.

Treatment with a single intramuscular injection of benzathine penicillin G led to complete healing within two weeks. By three months, the patient’s antibody levels had fallen fourfold. The case was reported by Dr. Ahmed Bakr Elazab and Dr. Ahmed Ibrahim (Department of Dermatology, Andrology & STDs, Faculty of Medicine, Suez University, Egypt) and Dr. Islam Mohamed Eldisoky (Sheikh Jaber Al‑Ahmad Al‑Sabah Hospital, Kuwait).

Why This Case Matters: A Classic Disease With an Unusual Face

Syphilis is often called “the great imitator” because it mimics many other conditions. When a chancre appears outside the genitals, it can easily be mistaken for traumatic mouth ulcer, herpes simplex, canker sore, squamous cell carcinoma, cutaneous tuberculosis, or deep fungal infection.

In this case, the key distinguishing feature was the painless, indurated edge of the ulcer. Between 40% and 70% of extragenital chancres occur in or around the mouth, with the lips accounting for about half. Yet because this presentation is rarely seen in routine practice, misdiagnosis is common. Here, the patient received ineffective topical antibiotics for weeks before the correct diagnosis was made.

The Takeaway: Test Syphilis in Any Chronic, Painless Lip Ulcer

The lesson is clear: any lip ulcer that is painless, firm, and persists beyond two to three weeks should prompt syphilis testing, even if the presentation does not fit the typical genital picture.

This matters not only for the patient but also for public health. Syphilis rates are rising worldwide, and missed diagnoses in the early, highly infectious stage drive further transmission. In this case, a simple blood test and a single antibiotic injection achieved complete cure — but only because syphilis was considered as a possibility.

The authors note that the absence of a tissue biopsy is a limitation, and they call for greater awareness among dermatologists, general practitioners, and oral medicine specialists who are often the first to see patients with persistent lip ulcers.

Read the published article here: https://bit.ly/4gqbNFH

JOURNAL

The Open Dermatology Journal

DOI: 10.2174/0118743722459596260427103418

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