Diagnostic Approach and Management
This patient requires CT abdomen and pelvis with IV contrast to identify the cause of positional flank pain, as the mildly elevated lipase (145) with normal urinalysis and absence of typical pancreatitis symptoms suggests a non-pancreatic etiology that warrants comprehensive imaging. 1, 2, 3
Clinical Reasoning
The presentation is atypical for common causes of flank pain:
Pain pattern argues against renal colic: Classic renal colic presents as colicky, wave-like severe pain that is independent of body position and radiates to the groin or genitals 2. This patient's pain worsens with sitting/kneeling and improves with standing, suggesting a musculoskeletal or positional component 2.
Normal urinalysis reduces likelihood of urolithiasis: While over 20% of patients with confirmed urinary stones may have negative urinalysis 2, the absence of hematuria combined with the positional nature of pain makes stone disease less likely 1.
Mildly elevated lipase without typical pancreatitis features: The lipase of 145 (approximately 1.5x upper limit of normal, assuming ULN ~100) falls well below the 3-fold elevation required for pancreatitis diagnosis 4, 5, 6. Additionally, the patient lacks epigastric pain, nausea, vomiting, or other cardinal features of acute pancreatitis 1, 7, 8.
Why CT with Contrast is Indicated
Contrast-enhanced CT identifies alternative diagnoses in 15% of patients with flank/back pain and negative urinalysis without history of kidney stones 3. In one study of 350 patients with flank pain, 15% of those with negative urinalysis and no urolithiasis history had diagnoses best characterized by CT abdomen and pelvis with IV contrast 1.
The 4-day duration without worsening suggests a subacute process requiring definitive imaging 2. This is not self-limited acute pain that would resolve with conservative management alone.
IV contrast is superior to non-contrast CT when urinalysis is negative, as it better characterizes alternative diagnoses beyond urolithiasis 3. Non-contrast CT is primarily useful for detecting stones, which are less likely given the clinical picture 1.
Differential Diagnosis to Evaluate
The imaging should assess for:
Musculoskeletal causes: Pain occurring after prolonged static positioning (sitting/kneeling) is more likely to have a musculoskeletal origin, particularly involving paraspinal muscles, facet joints, or referred pain from lumbar spine pathology 2. However, the radiation to the abdomen and severity (8/10) warrant ruling out visceral pathology first.
Gastrointestinal pathology: Right colonic diverticulitis, inflammatory bowel disease, or infectious colitis can present with flank pain and mildly elevated lipase 2, 4. Elevated lipase has been reported in infectious colitis without pancreatitis 4.
Retroperitoneal processes: Retroperitoneal bleeding can present with diffuse abdominal, back, or lower quadrant abdominal pain 1. While less likely without trauma or anticoagulation, it should be excluded.
Gynecologic causes in women: Ovarian pathology, pelvic congestion syndrome, or endometriosis can cause flank pain 2, 3.
Management Algorithm
Immediate actions:
- Order CT abdomen and pelvis with IV contrast 1, 2, 3
- Provide pain control with NSAIDs (first-line for non-pancreatic abdominal pain) 1, 2
- Reassess within 1 hour; if pain fails to respond to analgesia, consider hospital admission 2, 3
Based on imaging results:
If imaging shows minimal or no acute pathology: Treat as musculoskeletal back pain with activity modification, superficial heat, and consider spinal manipulation or physical therapy 1, 9. The positional nature strongly suggests a mechanical component.
If imaging reveals inflammatory bowel disease or colitis: The mildly elevated lipase may be explained by this finding 4. Refer to gastroenterology for management.
If imaging shows hydronephrosis or stone: Despite atypical presentation, manage according to stone size and degree of obstruction 2. Stones <5 mm typically pass spontaneously; larger stones may require intervention 2.
Critical Pitfalls to Avoid
Do not assume the mildly elevated lipase indicates pancreatitis: Lipase elevation <3-fold the upper limit of normal without typical clinical features does not meet diagnostic criteria for acute pancreatitis 5, 6. Other causes include infectious colitis, opioid use, abdominal trauma/surgery, and various non-pancreatic conditions 4, 6.
Do not delay imaging based on normal urinalysis: A normal urinalysis does not exclude significant urologic or other abdominal pathology 2, 3. The clinical picture warrants definitive imaging.
Do not overlook red flags: While not present in this case, be vigilant for fever (suggesting infection), hemodynamic instability, progressive neurological deficits, or signs of cauda equina syndrome, which would require urgent intervention 1, 9, 3.
Do not assume all flank pain is kidney-related: The positional nature of symptoms is a key distinguishing feature suggesting alternative etiologies 2.
Follow-up Plan
If symptoms persist beyond 4-6 weeks despite conservative management: Consider referral to physical therapy or pain management 1, 9.
Reevaluate at 1 month if symptoms do not improve: Earlier reassessment is warranted if symptoms worsen or new concerning features develop 9.
If CT reveals incidental findings requiring follow-up: Arrange appropriate specialty referral based on specific findings 1, 3.