What is the likely diagnosis and management for a 40-year-old male with right-sided abdominal pain, radiating to the lower back, initially scoring 7/10, now 2/10 after taking paracetamol (acetaminophen), with normal urination, bowel habits, and normal observations?

Right-Sided Abdominal Pain with Radiation to Lower Back in a 40-Year-Old Male

This clinical presentation most likely represents either a passing ureteral stone (given the colicky nature, radiation to back, and spontaneous improvement) or early appendicitis (given the right iliac fossa location), and you should perform graded compression ultrasonography of the right lower quadrant as the initial imaging study while monitoring for worsening symptoms. 1

Most Likely Differential Diagnoses

Ureteral Stone (Most Probable)

• The colicky nature of pain (7/10 severity, lasting 1.5 hours, then improving to 2/10), radiation to the lower back, and relief with movement strongly suggests a passing ureteral stone 2
• The normal urine dipstick does NOT rule out urolithiasis—microscopic hematuria is absent in 10-15% of confirmed ureteral stones 2
• The spontaneous improvement with paracetamol and time is consistent with stone passage 2

Appendicitis (Must Rule Out)

• Right iliac fossa pain in a 40-year-old male requires consideration of appendicitis, even without fever or leukocytosis 1
• The absence of classic features (anorexia, fever, migration of pain from periumbilical to RLQ) does NOT exclude appendicitis 2
• Early appendicitis can present with mild, intermittent pain before progression 1

Musculoskeletal Pain (Less Likely)

• The radiation to lower back and improvement with movement could suggest musculoskeletal origin 1
• However, the acute onset while driving and specific localization to right iliac fossa makes this less probable 2

Immediate Management Plan

Clinical Reassessment

• Perform serial abdominal examinations over the next 4-6 hours to assess for peritoneal signs (rebound tenderness, guarding, rigidity) 1, 2
• Check vital signs including temperature—fever would increase suspicion for appendicitis 1
• Assess for progression of pain intensity or change in character 2

Initial Imaging Strategy

• Perform graded compression ultrasonography of the right lower quadrant as the first-line imaging modality 1
• Ultrasonography is rated as "may be appropriate" (rating 6) for suspected appendicitis and avoids radiation exposure 1
• If ultrasonography is inconclusive or negative but clinical suspicion remains high, proceed to CT abdomen/pelvis with IV contrast (rating 8) 1

If Ureteral Stone is Suspected

• Obtain non-contrast CT of abdomen and pelvis (CT KUB protocol) if stone disease is the primary concern, as this is the gold standard for detecting urolithiasis 2, 3
• Non-contrast CT is superior to plain radiography for detecting stones and provides information about stone size, location, and degree of obstruction 3

Symptomatic Management

Pain Control

• Continue paracetamol (acetaminophen) 1000mg every 6 hours as needed, not exceeding 4000mg/24 hours 1
• If pain worsens or paracetamol is insufficient, add an NSAID such as ibuprofen 400-600mg three times daily or naproxen 500mg twice daily 1, 4
• NSAIDs provide superior pain relief compared to paracetamol alone for acute pain conditions 1

Activity and Monitoring

• Encourage normal activity and avoid bed rest, as movement may facilitate stone passage if urolithiasis is present 1
• Advise the patient to strain urine to capture any passed stones for analysis 2

Red Flags Requiring Urgent Evaluation

Immediately escalate care if any of the following develop:

• Fever >38°C (suggests infection/appendicitis) 1, 2
• Worsening pain intensity or development of peritoneal signs 1, 2
• Inability to tolerate oral intake or persistent vomiting 2
• Urinary retention or inability to void 1, 5
• Development of testicular pain (suggests referred pain from ureteral obstruction) 2

Follow-Up Strategy

If Symptoms Improve (Current Trajectory)

• Reassess in 24-48 hours to confirm continued improvement 4
• If pain resolves completely, consider outpatient follow-up in 1 week 4
• Advise patient to return immediately if symptoms worsen 2

If Symptoms Persist or Worsen

• Obtain definitive imaging (CT abdomen/pelvis with IV contrast for appendicitis concern, or non-contrast CT for stone disease) within 24 hours 1
• Consider surgical consultation if appendicitis is confirmed or if large obstructing stone is identified 1

Common Pitfalls to Avoid

• Do NOT dismiss this as simple musculoskeletal pain without imaging or close follow-up—appendicitis can present atypically in adults 2
• Do NOT rely solely on normal urine dipstick to exclude urolithiasis—hematuria may be absent 2
• Do NOT obtain plain abdominal radiographs as the initial imaging study—they have limited diagnostic value and are inferior to ultrasonography or CT 1, 3
• Do NOT delay imaging if pain worsens or peritoneal signs develop—perforated appendicitis has significantly worse outcomes 1