Differential Diagnoses for Sinusitis
The differential diagnosis of sinusitis includes allergic rhinitis (AR), eosinophilic nonallergic rhinitis (NAR), vasomotor rhinitis (VMR), and vascular headaches/migraines. 1
Primary Differential Diagnoses
Rhinitis Conditions
Allergic rhinitis typically presents with clear nasal discharge, nasal itching, sneezing, seasonal pattern, and response to antihistamines, distinguishing it from bacterial sinusitis which features purulent discharge and facial pain. 2
Eosinophilic nonallergic rhinitis should be considered in patients with chronic nasal symptoms without evidence of allergy or infection. 1
Vasomotor rhinitis presents with nasal symptoms triggered by environmental factors without allergic or infectious etiology. 1
Headache Disorders
- Vascular headaches and migraines are important differentials, as headache attributed to chronic sinusitis could actually be a migraine equivalent. 1
Distinguishing Bacterial Sinusitis from Viral URI
Key Diagnostic Criteria for Acute Bacterial Rhinosinusitis (ABRS)
Acute bacterial sinusitis should be suspected when upper respiratory tract infection symptoms persist beyond 10-14 days, or when symptoms worsen after initial improvement within 10 days (double-worsening pattern). 1, 2
Persistent symptoms (≥10 days): Purulent rhinorrhea, postnasal drainage, and facial pain correlate with increased likelihood of bacterial disease. 1
Double-worsening pattern: Symptoms initially improve but then worsen within 10 days. 2, 3
Severe presentation: Unusually severe symptoms in the first 3-4 days, particularly with high fever (>38.3°C/101°F) and purulent nasal discharge for 3+ consecutive days. 2, 3
Clinical Features Favoring Bacterial Sinusitis Over Viral URI
- Purulent nasal discharge (not clear) 1, 2
- Facial pain or pressure, especially unilateral 1, 4
- Maxillary dental pain 1, 4
- Poor response to antihistamines alone 2
- Symptoms persisting beyond typical viral URI duration (>10 days) 2, 4
Anatomic and Structural Considerations
Conditions Causing Ostiomeatal Obstruction
Nasal polyps and other anatomic variants can cause chronic obstruction mimicking infectious sinusitis. 1
Deviated nasal septum and other anatomic abnormalities should be assessed in recurrent cases. 1
Fungal Sinusitis Variants
Non-Invasive Forms
Fungal ball (mycetoma) presents with chronic unilateral symptoms, typically in maxillary or sphenoid sinuses, with dense accumulations of hyphae but no eosinophilic mucin. 1
Allergic fungal sinusitis involves eosinophilic mucin and should be distinguished histologically from fungal ball. 1
Invasive Fungal Sinusitis
Invasive fungal sinusitis (formerly mucormycosis) occurs in immunocompromised patients and presents with fever, headache, epistaxis, mental status changes, and insensate nasal ulcers—this requires aggressive debridement and systemic antifungal therapy. 1
Risk factors include: 1
- Diabetes mellitus
- Leukemia or solid malignancies with febrile neutropenia
- High-dose steroid therapy
- Severe impairment of cell-mediated immunity (transplant recipients, T-cell immunodeficiencies)
Predisposing Factors to Assess
Modifying Conditions
When evaluating recurrent acute rhinosinusitis or chronic rhinosinusitis, assess for: 1
- Environmental exposures 1
- Genetic predisposition 1
- Allergic rhinitis 1
- Rhinitis medicamentosa 1
- Cystic fibrosis 1
- Ciliary dyskinesia/immotile cilia syndrome 1
- Cocaine abuse 1
- Immunodeficiency 1
- Asthma 1
Common Pitfalls
Not all mucosal thickening on imaging represents active sinusitis—up to 40% of asymptomatic adults have abnormalities on sinus CT scans, so imaging findings must be correlated with clinical symptoms. 5
Overdiagnosis of bacterial sinusitis leads to inappropriate antibiotic use; most acute rhinosinusitis is viral and resolves without antibiotics. 4, 3
Failure to recognize migraine as the cause of "sinus headache" leads to inappropriate treatment. 1
Red Flags Requiring Immediate Evaluation
Patients should return immediately for orbital complications (eye pain, swelling, visual changes, periorbital edema) or neurological complications (severe headache, altered mental status, neck stiffness). 2
These warning signs suggest extension beyond uncomplicated rhinosinusitis and require urgent imaging and specialist consultation. 2