In a 24‑year‑old healthy male who developed acute burning low back pain radiating to the flanks, upper arms, calves and thighs after beginning soccer, without fever, urinary or neurological deficits, what is the most likely diagnosis and what first‑line conservative treatment should be recommended, and how should his concern about a possible sexually transmitted infection be addressed?

Diagnosis and Management of Acute Mechanical Low Back Pain Following New Athletic Activity

This is acute mechanical low back pain (muscle strain/paraspinal muscle injury) from overexertion in a new sport, and the first-line treatment is NSAIDs (ibuprofen 400 mg every 4-6 hours) combined with heat therapy, while the penile odor concern should be addressed separately with direct examination and STI screening if indicated. 1, 2

Most Likely Diagnosis: Acute Lumbar Muscle Strain

The clinical presentation strongly indicates acute mechanical low back pain from muscular overuse injury. 1, 3

Key Supporting Features:

• Clear temporal relationship: Pain onset Sunday morning immediately after starting a new high-intensity sport (soccer) with unfamiliar movement patterns 4, 5
• Typical pain distribution: Lumbar spine tenderness with radiation to flanks and diffuse muscle soreness in calves/thighs reflects delayed-onset muscle soreness (DOMS) from eccentric muscle loading 4
• Physical examination findings: Tenderness in lumbar paraspinal muscles, cervical paracervical muscles, and calf/thigh muscles on palpation with limited lateral flexion but preserved flexion/extension indicates muscular rather than structural pathology 1, 3
• Absence of red flags: No fever, no neurological deficits (normal strength, no numbness, no groin weakness), no bowel/bladder dysfunction, no history of trauma beyond athletic activity 6, 1

Why This Is NOT Spine Infection:

The IDSA guidelines specify that vertebral osteomyelitis should be suspected with new/worsening back pain PLUS fever, elevated ESR/CRP, or bloodstream infection 6. This patient has:

• No fever (explicitly stated) 6
• No risk factors: No IV drug use, no diabetes, no recent spine procedures, no immunosuppression 6
• Wrong timeline: Spine infection presents with indolent symptoms over weeks to months (average 2-4 months to diagnosis), not acute onset after a single athletic event 6

First-Line Conservative Treatment

Pharmacologic Management:

Ibuprofen 400 mg orally every 4-6 hours as needed is the evidence-based first-line medication. 1, 2

• The American College of Physicians recommends NSAIDs as first-line pharmacologic treatment for acute musculoskeletal injuries with moderate-certainty evidence for pain reduction and improved physical function 1
• FDA-approved dosing for mild-to-moderate pain is 400 mg every 4-6 hours; doses greater than 400 mg showed no additional benefit in controlled trials 2
• Maximum daily dose should not exceed 3200 mg 2
• Take with food or milk if gastrointestinal complaints occur 2

Non-Pharmacologic Management:

Heat therapy is equally important as first-line treatment alongside NSAIDs. 1

• Apply superficial heat (heating pad) to lumbar region for short-term pain relief 1
• The American College of Physicians identifies heat therapy as a cornerstone treatment with evidence showing short-term pain relief 1

Activity Modification:

Avoid prolonged bed rest; maintain activity as tolerated. 3, 4

• Prolonged bed rest should be avoided as atrophy occurs rapidly 4
• Current recommendation is only 2-3 days of rest maximum for acute radiculopathy; even less for simple muscle strain 3
• Gradual return to activity as pain permits 1

Imaging: NOT Indicated

No imaging is needed for this presentation. 1, 3

• The American College of Radiology states that routine imaging provides no clinical benefit for acute uncomplicated low back pain and leads to increased healthcare utilization without improving outcomes 1
• Imaging should only be considered if pain persists beyond 4-6 weeks despite conservative management 1
• This patient has no red flags warranting immediate imaging (no neurological deficits, no fever, no trauma beyond athletic activity, no cancer history) 1, 7

Expected Clinical Course and Follow-Up

Most patients with acute uncomplicated low back pain experience substantial improvement within the first month. 1, 3

Reassessment Timeline:

• If no improvement within 4-6 weeks, reassess for need for imaging or specialist referral 1, 3
• If neurological symptoms develop (weakness, numbness, bowel/bladder dysfunction), seek immediate re-evaluation 1

Addressing the STI Concern

The penile odor concern requires separate clinical evaluation and should not be conflated with the back pain diagnosis. 6

Appropriate Approach:

• Direct examination: Inspect the penis for discharge, lesions, rash, or signs of balanitis 6
• If examination is normal: Odor alone without discharge/lesions may represent normal smegma accumulation or hygiene issues; counsel on proper hygiene 6
• If any abnormality found: Obtain appropriate STI screening including gonorrhea/chlamydia NAAT, syphilis serology, HIV testing with pre/post-test counseling 6
• Partner discussion: One-year monogamous relationship reduces but does not eliminate STI risk; screening can be offered based on examination findings and patient concern 6

Key Point:

There is no pathophysiologic connection between STI and acute mechanical low back pain from athletic overexertion. The timing (pain started Sunday after soccer, odor concern mentioned separately) and clinical findings (muscular tenderness without systemic symptoms) confirm these are unrelated issues requiring separate evaluation.

Critical Pitfalls to Avoid

• Do not order imaging for acute uncomplicated mechanical back pain without red flags—this increases costs and healthcare utilization without benefit 1
• Do not prescribe opioids for acute musculoskeletal injury; NSAIDs are first-line 1
• Do not recommend prolonged bed rest; this causes rapid deconditioning 3, 4
• Do not assume STI causes back pain without evidence of systemic infection (fever, elevated inflammatory markers, neurological findings suggesting epidural abscess) 6
• Do not miss true red flags: If fever develops, neurological deficits emerge, or pain becomes severe/unrelenting at night, immediate re-evaluation with MRI is required 6, 1