What is the appropriate management for a patient presenting with flank pain and rash?

Management of Flank Pain and Rash

The presence of a rash with flank pain is atypical for uncomplicated urolithiasis and mandates evaluation for infectious or systemic causes, particularly herpes zoster, before pursuing standard stone imaging protocols. 1

Initial Clinical Assessment

The combination of flank pain and rash requires immediate differentiation between stone disease and infectious/systemic etiologies:

• Pain that worsens significantly with external flank pressure suggests infection (pyelonephritis or perinephric abscess) rather than stone disease. 1
• Pain from nephrolithiasis characteristically does NOT worsen with external pressure and presents with colicky waves of severe discomfort followed by less intense periods. 1, 2
• Any rash accompanying flank pain warrants evaluation for herpes zoster, particularly if the rash follows a dermatomal distribution. 3

Diagnostic Algorithm

If Infectious Etiology is Suspected:

• Order contrast-enhanced CT abdomen/pelvis rather than non-contrast CT to evaluate for pyelonephritis or abscess. 1
• Assess for systemic signs including fever, as life-threatening rashes often present with fever and require urgent intervention. 3
• Categorize the rash morphologically: petechial/purpuric, erythematous, maculopapular, or vesiculobullous to narrow the differential. 3

If Stone Disease Remains in the Differential:

• Non-contrast CT abdomen/pelvis is the gold standard for detecting urinary stones with 98-100% sensitivity and specificity, regardless of size, location, or composition. 1, 2
• However, contrast-enhanced CT may obscure stones within the renal collecting system if stone disease is the primary concern. 1, 4
• Ultrasound is appropriate for pregnant patients, those with radiation concerns, or when hydronephrosis has been identified. 1, 4

Critical Management Considerations

For Herpes Zoster (Shingles):

• If vesiculobullous rash in dermatomal distribution is present, initiate acyclovir 800 mg orally 5 times daily for 7-10 days. 5
• Treatment is most effective when started within 48 hours of rash onset and within 72 hours maximum. 5
• Acyclovir may be administered with or without food and requires dosage adjustment in renal impairment. 5

For Confirmed Stone Disease with Concurrent Rash:

• Manage the stone according to size and location per standard protocols, but continue to address the rash as a separate clinical entity. 1
• Asymptomatic simple renal cysts require no follow-up, while symptomatic cysts may require percutaneous drainage or surgical intervention. 4

Common Pitfalls to Avoid

• Do not anchor on nephrolithiasis diagnosis when a rash is present—this combination is atypical and suggests alternative pathology. 1
• Avoid non-contrast CT if infection is suspected, as it will not adequately evaluate for pyelonephritis or abscess. 1
• Do not use contrast-enhanced CT as first-line if stone disease is the primary concern, as it may obscure stones. 1, 4
• Consider pulmonary embolism in patients with isolated flank pain and risk factors, even without typical respiratory symptoms. 6
• Remember that flank pain with hematuria is not always nephrolithiasis—consider Page kidney (subcapsular hematoma causing secondary hypertension) in hypertensive patients. 7