Suggest Differential Diagnoses for This Woman with Pain in Her Lower Abdomen

Case presentation A 25-year-old woman presents to the ED complaining of lower abdominal pain. The pain had steadily increased in severity over the previous 24 hours and woke her from her sleep. The pain is constant, and simple analgesia has not helped. She has vomited once in the department.

Her menses are regular, and she is now on day 12 of her cycle. Premedical history No history of vaginal discharge or urinary symptoms. History of sexually transmitted disease two years ago, treated with antibiotics. Examination BP : 110/72 mmHg PR : 110/min  Temperature : 38.2°C Hb :14.7 g/dL  WCC : 16.6 × 10 9 /L  Platelets: 367 × 10 9 /L  Sodium : 139 mmol/L  Potassium : 4.1 mmol/L  Urea : 5.6 mmol/L  Creatinine : 74 μmol/L  CRP : 145 mg/L  Urine dipstick : NAD  Urinary b human chorionic gonadotropin (HCG) : Negative There is lower abdominal tenderness, more marked in the right iliac fossa, with…