How should flank pain be managed in an adult with acute pyelonephritis?

Management of Flank Pain in Acute Pyelonephritis

Administer intramuscular diclofenac 75 mg immediately to achieve pain relief within 30 minutes, and if pain persists after one hour, arrange immediate hospital admission. 1

Initial Pain Management Strategy

First-Line Analgesia

• Injectable non-steroidal anti-inflammatory drugs (NSAIDs), preferably diclofenac 75 mg intramuscularly, are the recommended first-line agents for acute flank pain in pyelonephritis because they provide rapid, reliable pain control within 30 minutes. 1
• Oral and rectal routes are considered unreliable for acute severe pain, and intravenous administration is impractical in most outpatient settings. 1
• The goal is complete or acceptable pain control maintained for at least six hours. 1

Alternative Analgesia When NSAIDs Are Contraindicated

• When NSAIDs are definitively contraindicated (e.g., history of gastrointestinal bleeding, severe renal impairment, or allergy), administer an opiate combined with an antiemetic, such as morphine sulfate with cyclizine, via intramuscular injection. 1

Monitoring and Escalation Protocol

One-Hour Reassessment

• Check pain response by telephone one hour after initial analgesic administration; a second visit is not required for this assessment. 1
• If pain has not been adequately relieved within 60 minutes, arrange immediate hospital admission by telephone. 1
• Abrupt recurrence of severe pain after initial improvement also warrants immediate hospital transfer. 1

Indications for Emergency Department Referral

• Patients with shock, fever with hemodynamic instability, or signs of systemic infection (confusion, leukocytosis, elevated creatinine) require immediate ambulance transport to the emergency department within one hour. 2
• The combination of altered mental status, leukocytosis, and acute kidney injury suggests sepsis or obstructive pyelonephritis—both life-threatening conditions that mandate urgent hospital evaluation. 2
• Obstructive pyelonephritis is a surgical emergency requiring immediate urinary decompression (percutaneous nephrostomy or ureteral stenting) and empiric intravenous antibiotics. 3

Outpatient Management for Responders

Home Care Instructions

• Instruct patients who achieve adequate pain control to drink large volumes of fluids and void urine through a tea strainer or gauze to capture any passed stones, which aids diagnosis. 1
• Provide clear instructions to contact their physician immediately if pain worsens or new distressing symptoms develop. 1

Follow-Up Assessment

• Perform a telephone follow-up one hour after the initial assessment to confirm sustained pain relief. 1
• All patients managed at home require subsequent investigation to determine whether a calculus was identified, its size and location, whether intervention is needed, and whether alternative diagnoses should be considered. 1

Critical Diagnostic Considerations

Distinguishing Pyelonephritis from Renal Colic

• The diagnosis of renal colic centers on a history of abrupt onset of severe unilateral flank pain radiating into the groin or genitals. 1
• Over 80% of patients with acute renal colic test positive for hematuria on urinalysis, supporting the diagnosis; however, absence of hematuria does not exclude the condition. 1
• A history of kidney stones makes nephrolithiasis the leading differential diagnosis in patients presenting with flank pain and pyuria. 4

Excluding Life-Threatening Diagnoses

• In patients over 60 years of age, consider a leaking abdominal aortic aneurysm as an alternative diagnosis requiring immediate hospital admission. 1
• In women of reproductive age, exclude ruptured ectopic pregnancy. 1
• Perform abdominal examination to establish the site of maximal tenderness and exclude signs of peritonitis; assess vital signs to exclude shock and systemic infection. 1

Imaging Strategy for Persistent or Severe Pain

When to Image

• Routine imaging is not indicated for uncomplicated pyelonephritis that is responding to therapy within the first 48–72 hours. 4
• Perform renal ultrasound immediately if there is flank swelling, a history of urolithiasis, renal function alterations, or elevated urine pH to rule out urinary obstruction, kidney stones, or abscess formation. 4
• If fever persists beyond 72 hours despite appropriate antibiotics or if clinical deterioration occurs, obtain contrast-enhanced CT abdomen/pelvis to evaluate for renal or perirenal abscess, obstruction, or emphysematous pyelonephritis. 4, 3

Imaging Modality Selection

• Renal ultrasound is the preferred initial imaging modality because it detects hydronephrosis, obstruction, and perinephric fluid with 100% sensitivity and 90% specificity, and it is safe in patients with bleeding history. 4
• Contrast-enhanced CT provides superior visualization of abscess formation, emphysematous changes, and complicated stone disease when ultrasound is inconclusive. 4

Common Pitfalls to Avoid

• Do not delay hospital admission for patients who fail to achieve pain relief within one hour of analgesia; this delay can result in missed diagnoses of obstruction or abscess. 1
• Avoid oral or rectal analgesics as first-line therapy for severe acute flank pain because absorption is unreliable in the setting of nausea and vomiting. 1
• Do not perform imaging in uncomplicated, clinically improving cases within the first 48–72 hours, as this exposes patients to unnecessary radiation and cost. 4
• Delaying imaging beyond 72 hours in patients with persistent fever can postpone diagnosis of abscess, obstruction, or other complications that require urgent intervention. 4