Diagnosis: Acute Cholecystitis
Despite the absence of fever, normal laboratory values, and no documented history of gallstones, acute cholecystitis (option b) remains the most likely diagnosis in this middle-aged patient presenting with RUQ pain, anorexia, vomiting, dehydration, and hypotension.
Clinical Reasoning
Why Cholecystitis is Most Likely
Classic presentation elements are present: The triad of RUQ pain, anorexia, and vomiting strongly suggests biliary pathology, with acute cholecystitis being the primary diagnostic concern in patients with acute RUQ pain 1.
Absence of fever does not exclude cholecystitis: While most patients with acute cholecystitis experience fever, the ACR guidelines explicitly state that clinical history, physical examination, and routine laboratory tests alone have not yielded acceptable likelihood ratios sufficient to predict the presence or absence of acute cholecystitis 1.
Normal labs are insufficient to exclude the diagnosis: Laboratory tests lack the diagnostic certainty needed for management decisions in suspected acute cholecystitis, which is why imaging plays the major role in establishing diagnosis 1.
Gallstones may be present but undetected: The absence of a documented history of gallstones does not mean they are absent—ultrasound has 96% accuracy for detecting gallstones, meaning some cases are missed, and acalculous cholecystitis (5-10% of cases) can occur without stones 1.
Why Other Options Are Less Likely
Pancreatitis (option a):
- Pancreatitis typically presents with epigastric pain radiating to the back, not isolated RUQ pain 2, 3.
- The diagnosis requires amylase/lipase ≥3× upper limit of normal, which contradicts the "all labs are normal" statement 3.
- While painless acute pancreatitis exists, it is exceedingly rare and typically presents with hypotension and altered mental status rather than prominent RUQ pain 4.
Cholangitis (option c):
- Cholangitis classically presents with Charcot's triad (fever, jaundice, RUQ pain) or Reynolds pentad (adding hypotension and altered mental status) 1.
- The absence of fever and jaundice makes cholangitis unlikely 1.
- Normal laboratory values would be atypical, as cholangitis typically shows elevated bilirubin and inflammatory markers 1.
Hepatitis (option d):
- Hepatitis typically presents with jaundice, elevated transaminases, and constitutional symptoms 1.
- The ACR guidelines specifically note that jaundice suggests a different subset of conditions requiring separate diagnostic algorithms 1.
- Acute hepatitis severe enough to cause hypotension would show markedly abnormal liver function tests 1.
Critical Diagnostic Approach
Immediate Next Step
- Obtain right upper quadrant ultrasound immediately: This is the first-choice investigation for biliary symptoms or RUQ pain, with 96% accuracy for detecting gallstones and ability to identify gallbladder wall thickening, pericholecystic fluid, and sonographic Murphy sign 1.
If Ultrasound is Inconclusive
Consider Tc-99m cholescintigraphy (HIDA scan): This has the highest sensitivity (97%) and specificity (90%) for acute cholecystitis, particularly useful when ultrasound findings are equivocal 1.
CT abdomen with IV contrast can identify complications such as gangrene, perforation, or alternative diagnoses if cholecystitis is not confirmed 1.
Important Clinical Caveats
Hemodynamic instability (hypotension) suggests complicated cholecystitis: This patient's hypotension and dehydration may indicate gangrenous cholecystitis, perforation, or sepsis, making this a surgical emergency requiring urgent imaging and surgical consultation 1.
Acalculous cholecystitis occurs in 5-10% of cases: This can develop in critically ill patients, those with severe dehydration, or following prolonged fasting, and may not show gallstones on imaging 1.
Do not delay imaging based on normal labs: The ACR guidelines emphasize that imaging studies play the major role in establishing diagnosis because clinical and laboratory findings alone are insufficient 1.