Differential Diagnosis for Sudden Onset of Severe Left Flank Pain

• Single Most Likely Diagnosis
  • Nephrolithiasis: This condition, also known as kidney stones, is a common cause of severe, spasmodic flank pain, often accompanied by nausea and vomiting. The patient's high caffeine intake, which can act as a mild diuretic and increase the concentration of substances in the urine that can form stones, supports this diagnosis. The sudden onset and severity of the pain, along with the location in the flank, are classic presentations for nephrolithiasis.
• Other Likely Diagnoses
  • Ruptured Ovarian Cyst: Although less common than nephrolithiasis in causing flank pain, a ruptured ovarian cyst can present with sudden, severe pain, often on one side. The patient's recent menstrual period and negative pregnancy test make this a plausible, though less likely, diagnosis.
  • Diverticulitis: While diverticulitis typically presents with left lower quadrant abdominal pain, it can occasionally cause flank pain if the affected diverticula are located in the upper parts of the sigmoid colon. However, the absence of fever, changes in bowel habits, or other gastrointestinal symptoms makes this less likely.
• Do Not Miss Diagnoses
  • Ectopic Pregnancy: Despite the negative B-HCG test, it's crucial to consider ectopic pregnancy in any woman of childbearing age presenting with severe abdominal or flank pain, as it can be life-threatening. However, the negative pregnancy test and the patient's presentation make this less likely.
  • Choledocholithiasis: This condition involves a gallstone obstructing the common bile duct and can cause severe abdominal pain, often radiating to the right flank or shoulder. While less likely given the left-sided pain, it's a critical diagnosis not to miss due to the potential for serious complications like pancreatitis or cholangitis.
• Rare Diagnoses
  • Other rare causes of severe flank pain might include renal infarction, pyelonephritis, or less common conditions like a renal artery aneurysm or a spontaneous hemorrhage. These would be considered if initial evaluations for more common causes are negative and the patient's condition does not improve or worsens.