What is the possible diagnosis for a patient with bilateral back pain, increased frequency of urination, and no fever?

Differential Diagnosis: Urinary Tract Infection with Possible Bilateral Pyelonephritis

The most likely diagnosis is a urinary tract infection (UTI), potentially involving the upper urinary tract (bilateral pyelonephritis), given the combination of bilateral back pain and increased urinary frequency, though the absence of fever and negative costovertebral angle (CVA) tenderness makes this presentation atypical. 1

Primary Diagnostic Consideration

Urinary Tract Infection (Most Likely)

• Increased urinary frequency is a cardinal symptom of cystitis (bladder infection), typically accompanied by dysuria and urgency 1
• The bilateral back pain could represent early or mild pyelonephritis, though this diagnosis is complicated by:
  • Absence of fever (pyelonephritis typically presents with fever and back pain/CVA tenderness) 1
  • Negative CVA tenderness (usually present in pyelonephritis) 1
• The presence of pyuria on urinalysis would strongly support UTI diagnosis, while its absence suggests another condition may be causing symptoms 1

Alternative Diagnoses to Consider

Nonspecific Mechanical Low Back Pain

• This is the most common cause of back pain in emergency settings 2, 3
• However, mechanical back pain typically does not present with urinary frequency changes 4
• The bilateral nature and association with urinary symptoms makes this less likely as the sole diagnosis 3

Ankylosing Spondylitis (Less Likely)

• Morning stiffness across the whole back that improves with exercise is pathognomonic for inflammatory spondyloarthropathy 5
• The patient's description lacks mention of morning stiffness or improvement with exercise 5
• Alternating buttock pain and awakening during the second part of the night are characteristic features not described here 5

Vertebral Osteomyelitis (Red Flag to Exclude)

• Fever is present in only up to 45% of bacterial vertebral osteomyelitis cases, so its absence does not exclude this diagnosis 6
• However, the acute onset (one week) and lack of risk factors (no mention of IV drug use, recent infection, immunocompromise, or indwelling catheters) make this less likely 6, 7
• The average time to diagnosis of vertebral osteomyelitis is 2-4 months, suggesting a more insidious presentation than described 6

Recommended Diagnostic Approach

Immediate Laboratory Testing

• Obtain urinalysis with microscopy to assess for pyuria - its presence supports UTI while absence suggests alternative diagnosis 1
• Urine culture if urinalysis is positive 1
• If suspecting vertebral osteomyelitis, obtain two sets of blood cultures and baseline ESR/CRP 6

Clinical Examination Priorities

• Repeat CVA tenderness assessment bilaterally 1
• Perform careful percussion of the spine to assess for vertebral osteomyelitis 6
• Assess for red flag symptoms including urinary retention (90% sensitivity for cauda equina syndrome), saddle anesthesia, fecal incontinence, or motor deficits 7

Imaging Considerations

• No imaging is required initially if this is nonspecific back pain without red flags 2, 3
• If vertebral osteomyelitis is suspected, spine MRI is recommended 6
• Imaging should be delayed 4-6 weeks for nonspecific mechanical back pain 3, 8

Critical Pitfalls to Avoid

• Do not dismiss the possibility of pyelonephritis based solely on absent fever and negative CVA tenderness - atypical presentations occur 1
• Do not delay evaluation if red flag symptoms develop, particularly urinary retention, which has 90% sensitivity for cauda equina syndrome 7
• Missing early vertebral osteomyelitis is common - maintain high suspicion in patients with risk factors even without fever 6, 7

Management Based on Most Likely Diagnosis

If urinalysis confirms UTI:

• For uncomplicated cystitis, treat with short-course antimicrobial therapy 1
• For pyelonephritis, fluoroquinolones are the mainstay of oral treatment, though resistance is increasing worldwide 1
• Consider antimicrobial resistance patterns in your geographic area when selecting therapy 1

If urinalysis is negative:

• Reassess for mechanical back pain and provide reassurance that symptoms typically resolve in 4-6 weeks 2, 3
• Acetaminophen and NSAIDs are first-line medications 3, 8
• Advise to stay active 3