Differential Diagnosis for Ongoing Intermittent Vaginal Bleeding

Single Most Likely Diagnosis

• Cervicitis or Cervical Erosion: This condition is often associated with post-coital bleeding, which fits the scenario of first noticing bleeding during sex. The light brown color of the bleeding could indicate old blood, which is consistent with intermittent bleeding.

Other Likely Diagnoses

• Vaginal Dryness or Atrophy: This condition, common in postmenopausal women or those with hormonal imbalances, can cause light bleeding, especially after sexual intercourse due to the lack of lubrication and thinning of the vaginal walls.
• Endometrial Polyps: These growths in the uterus can cause irregular, light bleeding, including post-coital bleeding. The bleeding is often light and can be brown in color.
• Intrauterine Device (IUD) Complications: If the patient has an IUD, especially a copper IUD, it could cause irregular bleeding, including light brown discharge or bleeding, especially after sexual intercourse.

Do Not Miss Diagnoses

• Cervical Cancer: Although less likely, cervical cancer must be considered, especially if the bleeding persists or increases. Post-coital bleeding is a classic symptom that warrants further investigation, including a Pap smear and possibly a colposcopy.
• Endometrial Cancer: This is another critical diagnosis not to miss. Risk factors include obesity, age over 40, and postmenopausal status. Irregular vaginal bleeding, including light brown discharge, can be a symptom.
• Pelvic Inflammatory Disease (PID): While PID typically presents with more pronounced symptoms like pelvic pain and fever, it can sometimes cause irregular bleeding. It's a diagnosis that should not be overlooked due to its potential for serious complications.

Rare Diagnoses

• Vaginal Cancer: This is a rare type of cancer but could present with irregular vaginal bleeding, including post-coital bleeding.
• Uterine Sarcoma: A rare tumor of the uterus that could cause irregular bleeding, including light brown discharge.
• Foreign Body in the Vagina: Although more common in children, a foreign body in the vagina can cause bleeding and discharge in adults as well, especially if it leads to infection or ulceration.

Each of these diagnoses requires careful consideration of the patient's full medical history, a physical examination, and possibly further diagnostic testing to determine the cause of the bleeding.