# Allergic Rhinitis: Pathophysiology and Treatment

## Introduction

**Allergic rhinitis** is a chronic inflammatory condition of the nasal mucosa mediated by IgE-dependent immune responses to inhaled allergens. It affects approximately **20-30% of the adult population** and significantly impacts quality of life, work productivity, and sleep. Understanding the underlying immunologic mechanisms and treatment hierarchy is essential for the otolaryngologist.

## Classification

### By Temporal Pattern
**Seasonal allergic rhinitis**: triggered by outdoor aeroallergens (tree, grass, weed pollens, mold spores). **Perennial allergic rhinitis**: triggered by year-round allergens (dust mites, pet dander, cockroach, mold).

### ARIA Classification (Allergic Rhinitis and its Impact on Asthma)

| Duration | Severity |
|----------|----------|
| **Intermittent**: <4 days/week OR <4 consecutive weeks | **Mild**: Normal sleep, daily activities, work/school |
| **Persistent**: ≥4 days/week AND ≥4 consecutive weeks | **Moderate-severe**: Impairment in ≥1 domain |

**Intermittent**: symptoms <4 days/week or <4 consecutive weeks. **Persistent**: symptoms >4 days/week and >4 consecutive weeks. **Mild**: normal sleep, daily activities, work/school performance. **Moderate-severe**: impairment in one or more of the above domains.

## Pathophysiology

### Early Phase (Minutes)
Allergen exposure leads to cross-linking of **IgE on mast cells** in the nasal mucosa. Mast cell degranulation releases **histamine, tryptase, leukotrienes, prostaglandins**. Results in: sneezing, rhinorrhea, pruritus, congestion within minutes.

### Late Phase (4-8 Hours)
Recruitment of **eosinophils, basophils, T-helper 2 (Th2) lymphocytes** to the nasal mucosa. Release of cytokines: **IL-4, IL-5, IL-13** perpetuate inflammation. Prolonged nasal congestion, mucosal edema, mucus hypersecretion. Accounts for persistent symptoms and **nasal priming** (increased sensitivity to lower allergen doses).

### Immunologic Basis
**Type I hypersensitivity reaction** (Gell and Coombs classification). Antigen-presenting cells process allergen and present to Th2 cells. Th2 cells produce IL-4 (promotes B-cell class switching to IgE) and IL-5 (eosinophil recruitment). IgE binds to high-affinity receptors (FcepsilonRI) on mast cells and basophils.

![Diagram illustrating the immunologic cascade of allergic rhinitis from allergen exposure through mast cell degranulation](/images/allergic-rhinitis-pathophysiology.jpg)

## Clinical Presentation

**Cardinal symptoms**: rhinorrhea (clear, watery), nasal congestion, sneezing, nasal pruritus. **Associated symptoms**: postnasal drip, eye symptoms (itching, tearing, redness), palatal pruritus, ear fullness. **Physical findings**: pale, boggy, bluish turbinates; clear rhinorrhea; allergic shiners (infraorbital darkening); transverse nasal crease (allergic salute); Dennie-Morgan lines. **Comorbidities**: asthma (up to 40% of allergic rhinitis patients), sinusitis, otitis media with effusion, nasal polyposis, sleep disturbance.

## Diagnostic Workup

### Skin Prick Testing
**Gold standard** for identifying specific allergen sensitivities. Rapid results (15-20 minutes), high sensitivity, Must withhold antihistamines for 5-7 days before testing, Tests common regional aeroallergens.

### Serum-Specific IgE (ImmunoCAP)
Alternative when skin testing is not feasible (dermatographism, severe eczema, inability to stop antihistamines). Comparable specificity to skin testing; slightly lower sensitivity.

### Nasal Endoscopy
Assess for turbinate hypertrophy, nasal polyposis, septal deviation, adenoid hypertrophy (children). Rule out other causes of nasal obstruction.

![Endoscopic view of pale, edematous inferior turbinates characteristic of allergic rhinitis](/images/allergic-rhinitis-endoscopy.jpg)

## Treatment

### Environmental Control and Allergen Avoidance
Dust mite avoidance: encasements, HEPA filters, humidity control (<50%). Pet dander: removal from bedroom, HEPA filters. Pollen: window closure during high pollen counts, nasal saline irrigation. Evidence for avoidance measures alone is modest but recommended as adjunctive therapy.

### Pharmacotherapy
**Intranasal corticosteroids (INCS)**: most effective single agent for all symptoms; fluticasone, mometasone, budesonide; onset in 12 hours, peak efficacy in days-weeks. **Second-generation oral antihistamines**: loratadine, cetirizine, fexofenadine; effective for sneezing, rhinorrhea, pruritus; minimal sedation. **Intranasal antihistamines**: azelastine, olopatadine; rapid onset; can be combined with INCS. **Combination sprays**: azelastine/fluticasone (Dymista) — superior to either agent alone. **Leukotriene receptor antagonists**: montelukast; less effective than INCS; useful for comorbid asthma. **Oral/topical decongestants**: short-term use only; risk of rhinitis medicamentosa with topical use >3-5 days. **Intranasal anticholinergics**: ipratropium bromide; targets rhinorrhea specifically. **Nasal saline irrigation**: adjunctive therapy for all patients.

### Immunotherapy
**Subcutaneous immunotherapy (SCIT)**: escalating doses of allergen extract; 3-5 year course; disease-modifying. **Sublingual immunotherapy (SLIT)**: tablets or drops; FDA-approved for grass, ragweed, dust mite. Indications: moderate-severe symptoms, inadequate response to pharmacotherapy, desire to reduce medication burden. Only treatment that alters the natural disease course and prevents new sensitizations.

### Surgical Options
**Inferior turbinate reduction**: for medication-refractory nasal obstruction due to turbinate hypertrophy. Techniques: submucosal resection, radiofrequency ablation, microdebrider-assisted turbinoplasty. Surgery addresses obstruction, not the allergic inflammatory process.

![Treatment algorithm for allergic rhinitis showing stepwise escalation from avoidance to immunotherapy](/images/allergic-rhinitis-treatment-algorithm.jpg)

## Key Clinical Pearls

**Intranasal corticosteroids** are the most effective monotherapy for allergic rhinitis and should be first-line for moderate-severe disease. Allergic rhinitis is a risk factor for **asthma development** — the unified airway concept supports treating nasal disease to improve lower airway outcomes. **Immunotherapy** is the only treatment that modifies the natural history of allergic disease. Persistent unilateral nasal symptoms should prompt investigation for alternative diagnoses (neoplasm, CSF leak, foreign body). Topical decongestant use beyond **3-5 days** risks rhinitis medicamentosa.

## References

1. Bousquet J, Khaltaev N, Cruz AA, et al. Allergic Rhinitis and its Impact on Asthma (ARIA) 2008 Update. *Allergy*. 2008;63(Suppl 86):8-160.
2. Seidman MD, Gurgel RK, Lin SY, et al. Clinical practice guideline: allergic rhinitis. *Otolaryngol Head Neck Surg*. 2015;152(1 Suppl):S1-S43.
3. Wheatley LM, Togias A. Clinical practice: allergic rhinitis. *N Engl J Med*. 2015;372(5):456-463.
4. Durham SR, Penagos M. Sublingual or subcutaneous immunotherapy for allergic rhinitis? *J Allergy Clin Immunol*. 2016;137(2):339-349.