**Question:** A 30 year old man had sexual exposure to a commercial sex worker, develops a painless indurated ulcer on gland after 3 weeks. Diagnosis is -

A. Syphilis
B. Chancroid
C. Genital Herpes
D. Genital Ulcer Disease

**Core Concept:**

Syphilis is a sexually transmitted disease caused by the bacterium Treponema pallidum. It affects various systems in the body, particularly causing an ulcer on the genitals. Syphilis is known as the "great imitator" due to its ability to mimic other diseases in clinical presentation.

**Why the Correct Answer is Right:**

D. Genital Ulcer Disease is the correct answer because the patient has developed a painless indurated ulcer on the genitals after a 3-week incubation period following sexual exposure to a commercial sex worker. This clinical presentation is characteristic of syphilis, which is a common cause of genital ulcers.

**Why Each Wrong Option is Incorrect:**

A. Syphilis is characterized by a painless indurated ulcer, but it is uncommon to present with a single ulcer. Furthermore, syphilis typically presents with a "target" or "raised" ulcer.
B. Chancroid is another sexually transmitted disease causing genital ulcers. However, chancroid typically presents with multiple small, tender ulcers, while the patient in this case has a single painless ulcer.
C. Genital Herpes presents with painful ulcers and is less likely to cause a single painless ulcer without other symptoms like vesicles or blisters.

**Clinical Pearl:**

In the context of a patient presenting with a single painless ulcer on the genitals, a high index of suspicion is warranted for syphilis, as it can often mimic other STIs or non-specific conditions. The clinical presentation, along with the patient's history of sexual exposure, can help guide the diagnosis. Early diagnosis and treatment of syphilis are crucial to prevent complications and reduce transmission to partners.