What workup is indicated for a patient with recurrent sinus infections and a constant low‑grade fever?

Workup for Recurrent Sinus Infections with Constant Low-Grade Fever

For a patient with recurrent sinus infections and constant low-grade fever, you should obtain a CT scan of the paranasal sinuses, perform nasal endoscopy, and conduct an immunologic workup including immunoglobulin levels (IgG, IgA, IgM, IgG subclasses) and pneumococcal antibody titers before and after pneumococcal vaccination 1, 2, 3.

Key Diagnostic Distinction

First, clarify whether this represents recurrent acute rhinosinusitis (multiple distinct episodes with complete resolution between) versus chronic rhinosinusitis (persistent symptoms >12 weeks). The constant low-grade fever suggests either ongoing chronic inflammation or an underlying immunologic problem rather than simple viral episodes 1.

Essential Workup Components

Imaging

• CT scan of paranasal sinuses is mandatory for recurrent or chronic disease 1, 4
• This differs from acute sinusitis where imaging is NOT recommended 5
• CT helps confirm diagnosis, assess extent of disease, identify anatomic variations, and guide potential surgical planning

Nasal Endoscopy

• Direct visualization of the middle meatus and sinus drainage pathways 1, 4
• Can identify polyps, anatomic obstruction, purulent drainage, or fungal elements
• Allows for culture collection if needed (endoscopically-guided middle meatus swab correlates 80-85% with antral puncture) 4

Immunologic Evaluation

This is critically important but often overlooked in recurrent/refractory cases 2, 3:

Initial immune workup should include:

• Quantitative immunoglobulins: IgG, IgA, IgM, IgE
• IgG subclasses (IgG1, IgG2, IgG3, IgG4)
• Pneumococcal antibody titers (pre- and post-vaccination with pneumococcal vaccine)

Why this matters: Studies show immunodeficiency is prevalent in recurrent sinusitis. In one series, 22 of 245 patients (9%) with therapy-refractory chronic rhinosinusitis had immunoglobulin deficiencies—5 with common variable immunodeficiency and 17 with IgG subclass deficiency 3. Three patients with IgG subclass deficiency had polysaccharide-specific immunodeficiency only revealed by poor pneumococcal vaccine response 3.

Additional Assessments

• Allergy testing (skin testing or specific IgE) if allergic rhinitis suspected 1, 2
• Consider testing for:
  • Cystic fibrosis (sweat chloride, genetic testing) in appropriate clinical context
  • Ciliary dyskinesia if history suggests (chronic otitis, bronchiectasis, situs inversus)
  • Fungal sinusitis markers if immunocompromised or imaging suggests

Clinical Pitfalls to Avoid

1. Don't perform surgery before completing immunologic workup 2. Identifying and treating immune deficiency can enhance surgical visualization, minimize complications, improve outcomes, or potentially obviate surgery altogether.

2. Don't assume IgG subclass deficiency alone is clinically significant—you must demonstrate functional antibody deficiency with pneumococcal titers 3. Some patients with low IgG subclasses respond normally to vaccination.

3. Don't overlook odontogenic causes—consider dental sources, especially if maxillary sinuses predominantly involved 5.

4. The constant low-grade fever is a red flag that distinguishes this from typical recurrent viral rhinosinusitis and warrants the more extensive workup described above.

Treatment Implications Based on Findings

• If common variable immunodeficiency or functional antibody deficiency identified: Consider immunoglobulin replacement therapy 3
• If allergic disease identified: Intranasal corticosteroids, allergen avoidance, possible immunotherapy 1, 2
• If anatomic obstruction on CT/endoscopy: May require surgical correction after medical optimization 1, 4
• If fungal elements identified: Requires specific antifungal approach depending on type

The 2025 guideline emphasizes that recurrent acute rhinosinusitis and chronic rhinosinusitis require investigation for underlying modifying factors before assuming simple bacterial infection 5, 1.