31.1 Allergic Rhinitis & Acute Non-Anaphylactic Allergic Reactions

Allergic Rhinitis: Pathophysiology, Clinical Features & Diagnostic Assessment

Allergic rhinitis is a chronic inflammatory disorder of the nasal mucosa induced by an immunoglobulin E (IgE)-mediated hypersensitivity reaction following allergen exposure. It affects approximately 10% to 30% of adults and up to 40% of children globally, presenting significant morbidity, sleep disturbance, impairment of academic or occupational performance, and exacerbation of comorbid conditions including asthma, rhinosinusitis, and otitis media.

Immunologic Pathophysiology

Allergic rhinitis exemplifies a classic Gell and Coombs Type I (immediate-type) hypersensitivity reaction, progressing through three distinct phases:

1. Sensitization Phase:

   • Inhaled aeroallergens penetrate the nasal epithelial barrier and are captured, processed, and presented by local dendritic cells (antigen-presenting cells) via major histocompatibility complex (MHC) class II molecules to naive CD4+ T helper cells.
   • In genetically susceptible atopic individuals, naive T cells differentiate into Th2 helper lymphocytes under the influence of interleukin-4 (IL-4).
   • Activated Th2 cells secrete a characteristic cytokine profile:
     • IL-4 and IL-13: Drive B-cell immunoglobulin class switching to synthesize allergen-specific IgE antibodies.
     • IL-5: Promotes eosinophil differentiation, maturation, bone marrow release, and survival.
   • Allergen-specific IgE binds with high affinity to Fc-epsilon-RI (FcεRI) receptors located on the surface of mucosal mast cells and circulating basophils, leaving the mucosa primed and sensitized.

2. Early-Phase Reaction (Minutes):

   • Upon subsequent re-exposure to the specific aeroallergen, multivalent allergen molecules cross-link adjacent IgE antibodies bound to FcεRI on sensitized mast cells.
   • Cross-linking triggers rapid intracellular calcium influx, cytoskeletal rearrangement, and immediate mast cell degranulation within 5 to 15 minutes.
   • Pre-formed and rapidly synthesized inflammatory mediators are released:
     • Histamine: Stimulates sensory H1 receptors on trigeminal unmyelinated C-fibers, triggering the sneeze reflex and intense mucosal pruritus. Histamine also stimulates H1 and H2 receptors on mucosal capillaries and post-capillary venules, inducing endothelial cell contraction, increased vascular permeability, plasma exudation, and profound mucosal edema.
     • Prostaglandin D2 (PGD2) & Cysteinyl Leukotrienes (LTC4, LTD4, LTE4): Potent vasodilators that dramatically increase nasal airway resistance and stimulate seromucous glands to produce copious watery secretions (rhinorrhea).
     • Tryptase and neutral proteases: Cleave extracellular matrix and amplify local neurogenic inflammation.

3. Late-Phase Reaction (4 to 8 Hours Post-Exposure):

   • Cytokines (IL-4, IL-5, IL-13, TNF-alpha) and chemokines (eotaxin/CCL11, RANTES/CCL5) synthesized during the early phase recruit inflammatory leukocytes into the nasal submucosa, predominantly eosinophils, basophils, neutrophils, and Th2 lymphocytes.
   • Recruited eosinophils degranulate, discharging cytotoxic basic proteins: major basic protein (MBP), eosinophil cationic protein (ECP), and eosinophil peroxidase (EPO).
   • These cytotoxic granule proteins cause nasal epithelial desquamation, mucosal hyperresponsiveness to nonspecific irritants (such as tobacco smoke, cold air, and strong perfumes), and persistent tissue inflammation.
   • Nasal congestion (airway obstruction) is the dominant clinical hallmark of the late-phase reaction due to sustained venous pooling in the cavernous sinusoids of the inferior turbinates and prolonged submucosal interstitial edema.

                     IMMUNOLOGIC CASCADE OF ALLERGIC RHINITIS

     Aeroallergen Exposure
             │
             ▼
     Dendritic Cell Antigen Presentation ──> Th2 Differentiation (IL-4)
             │                                      │
             │                                      ├─> IL-4 / IL-13 ──> B-cell IgE Synthesis
             │                                      └─> IL-5 ─────────> Eosinophil Activation
             ▼
     Sensitization: IgE binds FcεRI on Mast Cells
             │
   [Re-exposure]
             ▼
     Allergen Cross-links IgE ──> Degranulation (5-15 min)
             │
             ├─> EARLY PHASE: Histamine, PGD2, LTC4/D4
             │   • Sneezing (trigeminal stimulation)
             │   • Pruritus (palate, nose, eyes)
             │   • Watery rhinorrhea (glandular hypersecretion)
             │
             └─> LATE PHASE (4-8 hours): Eosinophil / Th2 Infiltration
                 • Cytotoxic proteins (MBP, ECP)
                 • Submucosal venous pooling & sustained edema
                 • Severe nasal congestion & mucosal hyperresponsiveness

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Aeroallergen Classification: Seasonal vs. Perennial

Accurate identification of aeroallergen triggers guides environmental avoidance and pharmacotherapy scheduling:

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Clinical Presentation & Physical Examination Findings

Diagnosis of allergic rhinitis is clinical, established by a compatible history of allergen-induced symptoms supported by targeted physical examination findings.

History and Cardinal Symptoms

• Paroxysmal Sneezing: Typically occurring in bursts of 5 to 10 sneezes upon waking or immediately upon allergen encounter.
• Clear Anterior and Posterior Rhinorrhea: Thin, watery, non-purulent secretions. Posterior drainage triggers a scratchy throat, frequent throat-clearing, and a dry nocturnal cough.
• Nasal Congestion / Obstruction: Bilateral or alternating nasal blockage, leading to habitual mouth breathing, snoring, sleep fragmentation, daytime fatigue, and hyposmia.
• Pruritus: Itching localized to the nasal tip, hard and soft palate, pharynx, and inner ears (via the Eustachian tube and tympanic plexus innervation).
• Ocular Symptoms (Allergic Rhinoconjunctivitis): Bilateral conjunctival erythema, tearing, chemosis (conjunctival edema), and severe periorbital pruritus.

Classic Physical Examination Stigmata

Careful head and neck examination reveals hallmark phenotypic signs of chronic atopic disease:

• Allergic Shiners: Symmetric, dark, bluish-purple hyperpigmentation under both lower eyelids. Caused by chronic venous stasis and venous pooling in the ethmoidal and infraorbital venous plexuses secondary to obstructed, swollen nasal turbinates.
• Dennie-Morgan Lines (Infraorbital Folds): Prominent transverse skin folds or creases beneath the margin of the lower eyelids, arising from recurrent eyelid edema and continuous spasm of the superior tarsal muscle.
• Allergic Salute & Transverse Nasal Crease: The "allergic salute" is the characteristic repetitive upward wiping or pushing of the nasal tip with the open palm to relieve itching and transiently dilate the anterior nasal valve. Over months to years, this upward mechanical pressure produces a permanent horizontal, hypopigmented or hyperpigmented line across the lower third of the nasal bridge—the transverse nasal crease.
• Allergic Gaping: Chronic mouth breathing resulting in an open-mouthed facial posture, dry chapped lips, and in children, altered dentofacial growth (high-arched palate, dental malocclusion).
• Posterior Pharyngeal Cobblestoning: Hypertrophy of lymphoid tissue along the posterior pharyngeal wall resembling cobblestones, driven by chronic postnasal drip and localized lymphoid follicular hyperplasia.

Anterior Rhinoscopy: Allergic vs. Non-Allergic Turbinates

Inspection of the nasal cavity using an otoscope with a wide speculum or nasal speculum is mandatory to distinguish allergic rhinitis from infectious and drug-induced etiologies:

           TURBINATE APPEARANCE: ALLERGIC vs. INFECTIOUS vs. MEDICAMENTOSA

     [Allergic Rhinitis]            [Viral Rhinosinusitis]        [Rhinitis Medicamentosa]
     • Pale, boggy, bluish-gray     • Beefy, erythematous, red     • Fiery red, swollen mucosa
     • Edematous turbinates         • Swollen turbinates           • Punctate submucosal bleeding
     • Copious clear, watery mucus  • Clear to mucopurulent mucus  • History of oxymetazoline >3-5 d

• Allergic Rhinitis: Nasal mucosa and inferior turbinates are characteristically swollen, edematous, boggy, and pale or bluish-gray (violaceous) in coloration, bathed in thin, clear, watery secretions.
• Infectious (Viral) Rhinitis: Nasal mucosa is erythematous, hyperemic, and beefy red, often with thick, cloudy, or mucopurulent discharge.
• Rhinitis Medicamentosa: Severely swollen, fiery red, hyperemic mucosa with punctate bleeding sites, accompanied by a history of topical decongestant spray overuse (e.g., oxymetazoline or phenylephrine) exceeding 3 to 5 consecutive days.

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Evidence-Based Pharmacotherapy for Allergic Rhinitis

The American Academy of Otolaryngology–Head and Neck Surgery (AAO-HNS) and the Allergic Rhinitis and its Impact on Asthma (ARIA) guidelines delineate a clear hierarchy of pharmacologic interventions based on symptom severity and chronicity.

Pharmacologic Class Comparison

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Intranasal Corticosteroids (INCS): The Gold Standard Monotherapy

Intranasal corticosteroids are the most potent and effective pharmacologic class for allergic rhinitis. Systematic reviews and clinical trials consistently demonstrate their superiority over oral antihistamines and leukotriene receptor antagonists for relieving all four cardinal symptoms, particularly nasal congestion.

Crucial Patient Counseling: Administration Technique

Improper administration is the leading reason for treatment failure and local adverse effects (epistaxis and septal perforation):

1. Clear Nasal Passages First: Gently blow the nose or perform saline nasal irrigation to clear excess mucus prior to dosing.
2. Head Position: Tilt the head slightly downward (chin tucked toward the chest), looking at the floor, rather than throwing the head backward (which causes the medication to drain into the throat, causing an unpleasant taste and systemic absorption).
3. Contralateral Hand Technique: Hold the spray bottle in the right hand to spray the left nostril, and in the left hand to spray the right nostril.
4. Spray Away from the Septum: Direct the nozzle laterally toward the outer corner of the ipsilateral eye or the ipsilateral ear tragus. Never direct the spray medially toward the nasal septum.
   • Why? Directing corticosteroid spray onto the anterior nasal septum (Kiesselbach's plexus) causes mucosal atrophy, chronic crusting, recurrent epistaxis, and rarely, full-thickness nasal septal perforation.
5. Gentle Inspiration: Breathe in gently through the nose as the spray is actuated; avoid vigorous sniffing, which draws the drug straight into the pharynx.

            CORRECT INTRANASAL CORTICOSTEROID DELIVERY TECHNIQUE

                   [Right Hand Sprays Left Nostril]

                             Forehead
                                │
                                ▼
           Left Eye ◄─────── Nozzle Aimed Laterally
                                │ (Toward Ipsilateral Ear / Outer Eye)
                                ▼
                         Nasal Septum [AVOID DIRECT CONTACT!]
                                │ (Prevents Epistaxis & Septal Perforation)
                                ▼
                             Chin Down

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Second-Generation Oral Antihistamines: Why First-Generation Agents Are Deprecated

Oral H1-antihistamines act as inverse agonists, stabilizing the inactive conformation of H1 receptors. Second-generation agents (cetirizine, fexofenadine, loratadine, desloratadine, levocetirizine) are standard of care:

• Lipophobicity and High Molecular Weight: Unlike first-generation compounds (diphenhydramine, hydroxyzine, chlorpheniramine), second-generation antihistamines do not readily cross the blood-brain barrier.
• Absence of Central Anticholinergic Side Effects: First-generation antihistamines block muscarinic, alpha-adrenergic, and serotonergic receptors, resulting in daytime sedation, cognitive blunting, dry mouth, blurred vision, constipation, urinary retention, and increased fall risk in elderly individuals. In children, they may cause paradoxical excitation.
• Fexofenadine Pearl: Completely non-sedating even at supratherapeutic doses because it is an active P-glycoprotein substrate excluded from the CNS. Must not be taken with fruit juices (grapefruit, orange, apple), which inhibit intestinal organic anion transporting polypeptide (OATP1A2), reducing fexofenadine bioavailability by up to 70%.
• Cetirizine Pearl: Fast onset of action (within 1 hour), but produces mild somnolence in approximately 10% of patients; best taken in the evening.

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Montelukast FDA Boxed Warning: Clear Clinical Indications

In March 2020, the U.S. FDA issued a Boxed Warning (Black Box) for montelukast regarding the risk of serious neuropsychiatric events:

• Reported events include: dream abnormalities, insomnia, anxiety, depression, agitation, aggressive behavior, hallucinations, and suicidal ideation and completed suicide.
• Guideline Mandate: Montelukast should NOT be prescribed as first-line or routine therapy for mild-to-moderate allergic rhinitis.
• Appropriate Clinical Indications: Reserve montelukast exclusively for patients who have an inadequate response or intolerance to INCS and oral antihistamines, OR for patients with allergic rhinitis with comorbid mild persistent asthma, where a single oral medication can target both upper and lower airway cysteinyl leukotriene-mediated inflammation.

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Allergen-Specific Immunotherapy (AIT): Disease Modification

Allergen immunotherapy is the only treatment modality that alters the natural history and underlying immunology of allergic rhinitis.

• Indications: Patients with confirmed IgE-mediated allergy (via skin prick testing or serum allergen-specific IgE) who have severe, persistent symptoms despite optimal pharmacotherapy, those intolerant of medications, or those wishing to avoid long-term drug use. AIT also prevents the subsequent development of allergic asthma in children with allergic rhinitis.
• Modalities:
  1. Subcutaneous Immunotherapy (SCIT): Weekly incremental allergen injections during the build-up phase (3-6 months), followed by monthly maintenance injections for 3 to 5 years. Carries a small risk of systemic anaphylaxis; must be administered in a clinic equipped with emergency resuscitation gear and observed for 30 minutes.
  2. Sublingual Immunotherapy (SLIT): Daily dissolvable oral tablets (FDA-approved for timothy grass, ragweed, and dust mites). First dose administered under medical supervision; subsequent doses self-administered at home. First-line home treatment requires an auto-injectable epinephrine prescription.
• Mechanism: Induces regulatory T cells (Tregs), secretes IL-10 and TGF-beta, suppresses Th2 responses, shifts antibody production from IgE to allergen-specific blocking IgG4, and diminishes tissue mast cell and basophil sensitivity.

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Acute Non-Anaphylactic Allergic Reactions: Acute Urticaria & Angioedema

Acute urticaria is defined by the sudden appearance of urticarial lesions (wheals), angioedema, or both, lasting less than 6 weeks in total duration.

Pathophysiology & Clinical Features

• The Wheal: A circumscribed, raised, erythematous lesion with a pale, swollen center, surrounded by an erythematous flare. It is accompanied by intense pruritus and is blanchable upon compression.
• Fleeting / Transient Nature: The hallmark distinguishing feature of urticaria is that individual lesions appear, evolve, and resolve completely within 24 hours (typically 2 to 12 hours) without leaving residual bruising, scaling, or hyperpigmentation.
  • Clinical Pearl / Diagnostic Red Flag: If individual lesions persist in the exact same location for >24 hours, are tender or burning rather than pruritic, and resolve with residual petechiae, ecchymosis, or post-inflammatory hyperpigmentation, the clinician must suspect urticarial vasculitis and obtain a skin punch biopsy.
• Angioedema: Involves mast cell degranulation in the deeper dermis, subcutaneous tissue, or submucosa. It produces non-pitting, non-pruritic, painful or burning swelling of the lips, eyelids, tongue, genitalia, or extremities, resolving more slowly over 48 to 72 hours.

Mandatory Triage: Ruling Out Anaphylaxis

Whenever an acute allergic reaction or urticaria presents, the clinician must immediately evaluate for life-threatening anaphylaxis:

• Respiratory: Laryngeal stridor, hoarseness, sensation of throat tightness, wheezing, dyspnea, persistent cough, SpO2 <92%.
• Cardiovascular: Hypotension (systolic BP <90 mmHg or >30% drop from baseline), diaphoresis, lightheadedness, syncope, tachycardia.
• Gastrointestinal: Severe crampy abdominal pain, repetitive projectile vomiting, diarrhea.
• Action: If any airway, respiratory, or circulatory compromise is present, administer Intramuscular Epinephrine (0.3 to 0.5 mg of 1:1,000 [1 mg/mL] solution into the mid-anterolateral thigh) immediately, activate EMS, and place the patient in the recumbent position with legs elevated.

Stepwise Management of Acute Non-Anaphylactic Urticaria

For isolated acute urticaria without respiratory compromise or hemodynamic collapse:

1. First-Line: Second-Generation H1-Antihistamines:
   • Initiate a modern second-generation oral H1-antihistamine (cetirizine 10 mg daily, fexofenadine 180 mg daily, or bilastine 20 mg daily).
   • Dose Up-Titration: International urticaria guidelines (EAACI/GA2LEN/WAO) strongly recommend that if symptoms persist at standard doses, the clinician should up-titrate the second-generation antihistamine up to 4 times the standard daily dose (e.g., cetirizine 20 mg BID or 40 mg daily; fexofenadine 180 mg BID or 360 mg daily) before adding secondary agents.
2. Second-Line Add-On: H2-Receptor Antagonists:
   • Cutaneous microvasculature possesses both H1 (85%) and H2 (15%) receptors. Adding famotidine (20 mg PO twice daily) can provide synergistic relief in patients unresponsive to high-dose H1 blockade.
3. Severe Acute Discomfort: Short-Course Systemic Corticosteroids:
   • For patients with severe, extensive, sleep-disrupting urticaria or significant facial angioedema, prescribe a short oral corticosteroid burst: Prednisone 40 mg PO daily for 3 to 5 days.
   • Prolonged courses or tapers are unnecessary for acute urticaria and carry substantial metabolic and bone toxicity risks. Long-term steroids are strictly avoided.
4. Avoid Triggers: Discontinue potential drug culprits (NSAIDs, ACE inhibitors, new antibiotics) and avoid alcohol, heat, tight clothing, and vigorous exercise during the acute flare.