A patient presents with sharp lower quadrant abdominal pain, a history of missed menses a few weeks earlier, brownish vaginal bleeding, and referred shoulder pain on the affected side. What is the most likely diagnosis?

• A. Ovarian torsion
• B. Appendicitis
• C. Pelvic inflammatory disease
• D. Ectopic pregnancy

Answer: (D)

The key idea is that reproductive-age patients with abdominal pain, light vaginal bleeding, and a history suggestive of pregnancy should be evaluated for an ectopic pregnancy, especially when there is referred shoulder pain. The sharp lower quadrant pain combined with missed menses weeks earlier points to pregnancy, and the brownish bleeding can be an early or abnormal bleed associated with ectopic implantation. Referred shoulder pain on the affected side signals diaphragmatic irritation from intraperitoneal blood, a classic clue that the ectopic pregnancy may have ruptured and is causing internal bleeding—an emergency.

Ovarian torsion would present with sudden, severe unilateral pain and is not typically linked to missed periods or shoulder pain. Appendicitis usually causes periumbilical evolving to right lower quadrant pain without a pregnancy history or shoulder sign. Pelvic inflammatory disease involves lower abdominal pain with vaginal discharge and cervical motion tenderness, not the shoulder pain or acute rupture scenario. Taken together, the presentation best fits an ectopic pregnancy, with rupture being a dangerous complication demanding urgent evaluation and care.