What is the diagnosis for a patient with a history of upper respiratory tract infection (URTI) symptoms, including clear runny nose and low-grade fever, that resolved, now presenting with purulent nasal discharge and frontal bone tenderness?

Diagnosis: Bacterial Sinusitis (ABRS)

This patient meets clinical criteria for acute bacterial rhinosinusitis (ABRS) based on the "double worsening" presentation pattern, characterized by initial viral URI symptoms that resolved, followed by new onset of purulent nasal discharge and frontal bone tenderness. 1, 2

Clinical Reasoning

This case demonstrates the classic "double-sickening" pattern that distinguishes bacterial sinusitis from uncomplicated viral URI:

Timeline Analysis

• Days 1-4: Clear runny nose and low-grade fever (typical viral URI) that completely resolved 2, 3
• Current presentation: New onset of purulent nasal discharge with frontal bone tenderness after initial improvement 1

Diagnostic Criteria Met

The patient fulfills one of three accepted presentations for ABRS according to multiple consensus guidelines 1, 2:

1. Persistent symptoms ≥10 days (not applicable here)
2. Severe onset with high fever (≥39°C) AND purulent discharge for 3-4 consecutive days (not applicable)
3. Worsening symptoms after initial improvement ✓ (this patient's presentation) 1, 2

Cardinal Symptoms Present

The patient demonstrates two of three cardinal features required for ABRS diagnosis 1:

• Purulent nasal discharge (anterior or posterior) ✓ 1
• Facial pain/pressure/fullness (frontal bone tenderness) ✓ 1
• Nasal obstruction (not explicitly mentioned but implied)

Why Not Simple URTI?

Key Distinguishing Features

Viral URIs naturally progress from clear to purulent discharge over several days due to neutrophil influx and desquamated epithelium, but they follow a predictable improvement pattern 2, 3. The American Academy of Pediatrics notes that uncomplicated viral infections last 5-7 days with respiratory symptoms peaking at days 3-6, then improving 1, 2.

This patient's biphasic course is the critical differentiator 2:

• Initial viral symptoms completely resolved (not just improved)
• New onset of purulent discharge and facial pain/tenderness after resolution
• This "double worsening" pattern is pathognomonic for secondary bacterial infection 1, 2

Common Pitfall to Avoid

Do not assume purulent discharge alone indicates bacterial infection 2, 3. The American Academy of Otolaryngology emphasizes that nasal discharge color is not a reliable indicator by itself, as viral infections naturally become purulent 2, 3. The diagnosis requires either:

• Persistence beyond 10 days, OR
• Severe onset (high fever + purulent discharge for 3-4 days), OR
• Worsening after initial improvement (this case) 1, 2

Clinical Implications

Frontal Bone Tenderness Significance

The presence of frontal bone tenderness with purulent discharge is particularly concerning 1, 4:

• Indicates frontal sinus involvement 4
• Warrants more aggressive management due to proximity to intracranial structures 4
• Male adolescents show notable preponderance for frontal sinusitis complications 4

Management Approach

Antibiotic therapy is indicated based on clinical diagnosis of ABRS 2, 5:

• First-line: High-dose amoxicillin or amoxicillin-clavulanate 5
• Duration: 5-7 days for uncomplicated cases with clinical improvement 2
• Assess for improvement after 3-5 days of treatment 2

Imaging is not required for uncomplicated ABRS diagnosis in this straightforward clinical presentation 1. However, CT should be considered if symptoms worsen or fail to improve with appropriate antibiotic therapy, given the frontal sinus involvement 1, 4.