**Question:** A 27-year-old male had burning micturition and urethral discharge. After 4 weeks he developed joint pains involving both the knees and ankles, redness of the eye and skin lesion. The most probable clinical diagnosis is:

A. Syphilis
B. Gonorrhea
C. Chlamydia
D. Trichomoniasis

**Correct Answer:** D. Trichomoniasis

**Core Concept:**
Trichomoniasis is a sexually transmitted infection (STI) caused by the protozoan parasite Trichomonas vaginalis. It primarily affects the genital tract but can also involve other parts of the body. The infection is transmitted through direct sexual contact with an infected individual.

**Why the Correct Answer is Right:**
The correct answer (D) is Trichomoniasis, as the patient presents with symptoms like burning micturition, urethral discharge, joint pains, redness of the eye, and skin lesions. These symptoms are characteristic of Trichomoniasis, particularly when present together.

Trichomoniasis can cause genital inflammation and ulceration which may lead to urethral discharge, urethral burning, and pain on micturition. The organism can spread through the bloodstream, causing skin lesions and eye inflammation. Joint pains are a rare but known complication of Trichomoniasis.

**Why Each Wrong Option is Incorrect:**
A. Syphilis (A) is caused by Treponema pallidum and presents with a different set of symptoms, including ulcers on the genitalia, lymphadenopathy, and systemic symptoms like fever, fatigue, and joint pain.

B. Gonorrhea (B) is caused by Neisseria gonorrhoeae and presents with symptoms like urethral discharge, urethral pain, epididymitis, and orchitis. It does not typically cause skin lesions or eye inflammation.

C. Chlamydia (C) is caused by Chlamydia trachomatis and presents with symptoms like urethral discharge, urethritis, cervicitis, and pelvic inflammatory disease (PID). It does not cause joint pains or skin lesions like Trichomoniasis.

**Clinical Pearls:**
1. Trichomoniasis is a sexually transmitted infection caused by Trichomonas vaginalis and can lead to skin lesions, eye inflammation, and joint pains due to its potential to spread via the bloodstream.
2. The diagnosis of STIs should be considered in patients presenting with genital symptoms and skin lesions.
3. Early diagnosis and treatment of STIs are crucial to prevent complications and transmission to partners.