What are the possible diagnoses for a 24-year-old female patient with sudden onset neck pain, photophobia, and elevated C-reactive protein (CRP), who recently had flu-like symptoms and has a history of menstrual cycle-related abdominal pain, with negative lumbar puncture (LP) and normal computed tomography (CT) head and neck scans?

Differential Diagnosis for 24-Year-Old Female with Acute Neck Pain and Elevated CRP

The most likely diagnosis in this patient is an upper respiratory tract infection with associated sinusitis and reactive myalgia, given the recent flu-like illness, current rhinitis, sinus tenderness, nonproductive cough, and markedly elevated CRP of 203 mg/L in the context of negative meningitis workup.

Critical Red Flags Already Excluded

• Meningitis has been effectively ruled out with negative lumbar puncture and resolution of photophobia, though the initial presentation with neck pain and photophobia appropriately prompted this evaluation 1
• Normal CT head/neck excludes structural pathology, mass lesions, and significant vascular abnormalities 1
• The negative LP with normal glucose, protein, and cell counts makes bacterial or viral meningitis extremely unlikely 1

Primary Diagnostic Considerations

1. Viral Upper Respiratory Infection with Myalgia (Most Likely)

• CRP elevation to 203 mg/L is consistent with acute viral infection, particularly influenza-like illness, where CRP correlates with symptom severity 2
• The recent flu-like symptoms "a few weeks ago" may represent incomplete resolution or reactivation of viral illness 2
• Bilateral neck pain without focal neurologic findings suggests muscular/myalgic origin rather than structural pathology 3
• New nonproductive cough with rhinitis and sinus tenderness indicates active upper respiratory process 1
• CRP levels of 100-200+ mg/L can occur with severe viral infections, though this level warrants careful exclusion of bacterial processes 4, 5

2. Acute Bacterial Sinusitis

• Localized tenderness over right frontal and maxillary sinuses with rhinitis suggests sinusitis 1
• CRP >100 mg/L raises concern for bacterial rather than purely viral sinusitis 4, 5
• Absence of purulent discharge does not exclude bacterial infection 1
• Neck pain can be referred from severe sinusitis or represent reactive cervical lymphadenopathy 1

3. Vertebral Osteomyelitis/Discitis (Must Exclude)

• CRP >100 mg/L with neck pain and fever history mandates consideration of spinal infection, even with normal CT 3, 4
• Critical pitfall: CT has only 6% sensitivity for epidural abscess and poor sensitivity for early osteomyelitis 3
• MRI cervical spine with and without contrast is mandatory if spinal infection remains a concern, with 96% sensitivity and 94% specificity 1, 3, 4
• However, several features argue against this:
  • Acute 3-day onset (osteomyelitis typically presents more insidiously over weeks) 3, 6
  • Pain improves with NSAIDs (less typical for infection) 3
  • No risk factors documented (IV drug use, diabetes, immunosuppression, recent procedures) 3, 4
  • Bilateral neck pain (osteomyelitis usually focal) 3

4. Viral Meningitis (Low Probability)

• While LP was negative, viral meningitis can occasionally present with normal CSF early in disease course 1
• Photophobia that clinically improved argues against progressive CNS infection 1
• Enterovirus and HSV-2 are most common causes of viral meningitis in adults, but typically show CSF pleocytosis 1
• The negative LP makes this diagnosis unlikely but not impossible 1

Diagnostic Algorithm

Immediate Actions Required:

1. Obtain blood cultures (2 sets) and complete blood count before any antibiotics 3, 4, 6

   • Blood cultures essential to identify bacteremia if present 4, 6
   • WBC with differential may show leukocytosis, though can be normal in 40% of infections 4

2. Measure ESR in addition to CRP 3, 4

   • ESR is highly sensitive for spinal infection and should be elevated if osteomyelitis present 3, 4
   • Normal ESR would significantly lower concern for vertebral osteomyelitis 4

3. Assess for additional risk factors for serious infection 3, 4:

   • IV drug use
   • Diabetes mellitus
   • Immunosuppression
   • Recent spine procedures
   • Indwelling catheters or dialysis
   • Recent bloodstream infections

Decision Point: MRI Cervical Spine

Order MRI cervical spine with and without IV contrast if ANY of the following are present 1, 3, 4:

• ESR >50 mm/hour
• Persistent fever or constitutional symptoms
• Any risk factors for spinal infection
• Progressive or severe pain despite adequate analgesia
• Any new neurologic symptoms
• Failure to improve within 48-72 hours of appropriate treatment

MRI can be deferred if 3:

• ESR normal or minimally elevated
• No risk factors for infection
• Clinical improvement with symptomatic treatment
• No neurologic deficits

Treatment Approach:

For presumed viral URI with sinusitis:

• Continue NSAIDs for symptomatic relief 5
• Consider empiric antibiotics for bacterial sinusitis given CRP >200 mg/L 4, 5
• Close clinical follow-up within 48-72 hours 3
• Strict return precautions for fever, worsening pain, neurologic symptoms, or failure to improve 3

Critical Clinical Pitfalls to Avoid

1. Fever is absent in up to 55% of bacterial vertebral osteomyelitis cases - absence of current fever does not exclude spinal infection 3

2. Average time to diagnosis of vertebral osteomyelitis is 2-4 months, with 34% initially misdiagnosed - maintain high index of suspicion 3

3. Normal CT does not exclude spinal infection - MRI is required if clinical suspicion remains 1, 3

4. CRP can be elevated during menstrual cycle (17% increase during menses), though not to this degree 7

5. Do not delay antibiotics if sepsis, hemodynamic instability, or progressive neurologic deficits develop 6

Monitoring Parameters

• Reassess CRP after 4 weeks if infection treated - CRP >27.5 mg/L indicates treatment failure 4
• Clinical reassessment within 48-72 hours to ensure improvement 3
• Any worsening or new neurologic symptoms require immediate MRI 3, 4