Allergic Rhinitis & Cold

ENT Anatomy and Physiology

• The Ear-Nose-Throat (ENT) Organs:

  • The ENT consists of three interconnected organs whose functions are closely linked.

  • Eustachian Tube: A critical structure that connects the ear with the nose and throat.

  • Clinical Significance: Because they are interconnected, a disorder in one of the organs is likely to implicate the physiological functions of the others.

• Host Defense at the Nose and Pharynx:

  • An intricate defense system protects against foreign particles (allergens) and infections using various stimulations:

    • Sensory: Responds to mechanical and thermal stimulation.

    • Cholinergic: Triggers dilation of arterial blood flow.

    • Sympathetic Stimulation: Triggers constriction of arterial blood flow.

  • Specific Structures and Functions:

    • Coarse Hairs: Located in the nose; function to remove large particles from inspired air.

    • Mucus Layer: Located on the outer layer of the respiratory mucosa; a thick, sticky layer that traps foreign and infectious particles.

    • Ciliated Epithelial Cells: Located on the inner layer of the respiratory mucosa; they sweep mucus toward the pharynx for excretion.

    • Mucus-Secreting Glands: Located in the respiratory mucosa; produce mucus, enzymes, and mediators to remove foreign materials.

Allergic Rhinitis (AR)

• Definition: Prominent, paroxysmal nasal symptoms affecting the upper respiratory system and eyes due to exposure to allergens.

• Prevalence: In Singapore, the prevalence is between $5.5\% - 13\%$, especially among children aged $4 - 17$ years old.

• Primary Causes and Allergens:

  • Indoor: Dust mites and cockroaches.

  • Outdoor: Pollen and haze from forest fires.

  • Occupational: Wood dust and industrial chemicals.

  • Atopy: Possibly due to the "Atopic (or Allergic) Triad" or a family history of atopy (genetic predisposition to allergic diseases).

• Types of Allergic Rhinitis:

  • Seasonal AR: Occurs at the same time every year (for a few months), such as during the release of pollen in Spring.

  • Perennial AR: Occurs throughout the year with worsening signs and symptoms (S/Sx) due to exposure to smoke, dusts, or dust mites. This is the predominant pattern observed in Singapore.

• Pathophysiology of AR:

  • Involves mast cells, IgE antibodies, and inflammatory mediators.

  • Sensitization (Initial Phase): Allergen enters the tissue/cells, alerting the production of IgE, which binds to mast cells.

  • Early Response: Happens when allergens come into contact with IgE on mast cells, leading to mast cell degranulation. This releases inflammatory mediators like histamines.

  • Late Response: Occurs approximately $6 - 12$ hours after exposure, resulting in sustained inflammation.

• Signs and Symptoms (S/Sx):

  • Early Symptoms (Minutes): Nasal Pruritus (sensory stimulation of itch and sneezes), fatigue, irritability, malaise, and triggers for other allergic symptoms like eczema or asthma.

  • Late Phase (Hours): Rhinorrhea (mucus secretion in nasal passage), Nasal Congestion (vasodilation, mucosal edema), postnasal drip, and allergic conjunctivitis.

• Physical Examination Findings:

  • Allergic Shiners: Dark circles under the eyes.

  • Allergic Salute: Rubbing the tip of the nose upward with the palm of the hand.

  • Allergic Crease: A horizontal crease just above the bulbar of the nose.

  • Allergic Gape: Open-mouth breathing, which may lead to dentofacial complications.

  • Dennie’s Lines: Wrinkles beneath the lower eyelids.

• Complications of Poorly Managed AR:

  • Asthma: Increased risk of exacerbation (atopic triad).

  • Acute Otitis Media: AR fluid drains through the Eustachian tube into the middle ear; bacteria replicate in entrapped fluid causing infection.

  • Bacterial Sinusitis: $30 - 80\%$ of cases are caused by AR, resulting in purulent discharge, congestion, and facial pain.

Allergic Rhinitis Management

• Classification by Frequency and Severity:

  • Intermittent: $< 4$ days per week OR $< 4$ weeks per stretch.

  • Persistent: $> 4$ days per week AND $> 4$ weeks per stretch.

  • Mild: Normal sleep, no impairment on activities, normal work/school, no troublesome S/Sx.

  • Moderate/Severe: At least one of the following: Abnormal sleep, impaired activities, impact on work/school, or troublesome S/Sx.

• Treatment Algorithm:

  • Mild-Intermittent: Antihistamines + Decongestant OR LTRA.

  • Mild Persistent / Moderate-Severe Intermittent: Antihistamine + Decongestant OR Intranasal CS OR LTRA.

  • Moderate-Severe Persistent: Intranasal CS AND (Antihistamine OR LTRA).

• Non-Pharmacological Management (Environmental Control):

  • Dust Mites: Use vacuuming and air-conditioning with HEPA filters.

  • Pets: Keeping pets (especially non-hypoallergenic ones) out of the bedroom and bathing them regularly.

  • Moulds: Using humidifiers or controlling humidity to remove sources of growth.

Upper Respiratory Tract Infections (URTI)

• Common Cold:

  • A self-limiting, benign condition caused mainly by Rhinovirus or Parainfluenza virus.

  • Risk Factors: Children, daycare, psychological stress, sleep disturbance, seasons (Fall to Spring), and being immunosuppressed (HIV, T2DM, cancer, CKD).

  • Transmission: Self-inoculation via formites (non-living surfaces) or aerosolization (breathing airborne particles from coughs/sneezes).

  • Pathophysiology: Inoculation/incubation for $24 - 72$ hours.

    • Humoral Cytokine Response: Causes systemic symptoms (fever, headache).

    • Local Inflammation: Release of prostaglandins (PG) and bradykinin causes local symptoms (sore throat, runny nose).

    • Duration: Symptoms persist for $3 - 13$ days.

• Clinical Presentation of Infection:

  • Signs (Measurable): Cough, fever, erythema of the throat.

  • Symptoms (Described): Rhinorrhea, nasal congestion, sore throat, headache, myalgia, fatigue.

Fever and Rhinitis Management

• Fever:

  • Characterized by a rise in body temperature above the set point regulated by the hypothalamus.

  • Measurement Ranges (Adults):

    • Oral: $35.5 - 37.5^\circ\text{C}$

    • Rectal: $36.5 - 38.0^\circ\text{C}$

    • Ear: $35.8 - 38.0^\circ\text{C}$

  • Management: Tepid sponging, hydration, monitoring temperature. Pharmacological options include Paracetamol and NSAIDs (Ibuprofen, Naproxen).

• Rhinitis (Viral):

  • Acute ($\le 4$ weeks) inflammation of nasal mucus membranes. Result of PG and bradykinin causing hypersecretion.

  • Symptoms: Rhinorrhea, nasal congestion, postnasal drips.

  • Complications: Viral/Bacterial Sinusitis or Sore Throat.

Pharmacology of Antihistamines

• Mechanism of Action: Competitively antagonize $H_1$ receptors to prevent histamine from inducing inflammatory responses.

• Histamine Receptors Overview:

  • $H_1$ Receptor: Located in smooth muscle, CNS, and endothelial cells. Causes itch, bronchoconstriction, vasodilation, and motion sickness.

  • $H_2$ Receptor: Located in the stomach; regulates gastric acid secretion.

• Generations of Antihistamines:

  • 1st Generation: High Lipophilicity (High LogP, passes Blood-Brain Barrier), Promiscuous (acts on multiple receptors), short duration of action.

    • Chlorpheniramine: $4\,\text{mg}$ every $6 - 8$ hours (TDS/QDS). Max: $24\,\text{mg/day}$.

    • Hydroxyzine: $25\,\text{mg}$ TDS/QDS PRN.

  • 2nd Generation: Poor LogP (peripheral action), specific to $H_1$, longer duration.

    • Loratadine (Clarityn): $10\,\text{mg}$ QD PRN.

    • Cetirizine (Zyrtec): $5\,\text{mg}$ BD or $10\,\text{mg}$ QD.

    • Levocetirizine: $2.5 - 5\,\text{mg}$ QD.

    • Desloratadine: $0.5\,\text{mg}$ QD.

  • 3rd Generation: Even longer duration, very specific.

    • Bilastine: $20\,\text{mg}$ QD.

• Adverse Effects and Cautions:

  • CNS $H_1$ Antagonism: Drowsiness and weight gain.

  • Cholinergic Antagonism (mostly 1st Gen): Dry mouth, constipation, urinary retention, blurred vision. Contraindicated in narrow-angle glaucoma, bladder neck obstruction, and BPH.

  • Adrenergic Antagonism: Hypotension and palpitations.

  • Counseling Rule: Patient should not drive or operate machinery if sedation occurs.

Pharmacology of Decongestants

• Mechanism of Action: Adrenergic agonists that increase $\alpha$-adrenergic receptor activity, leading to vasoconstriction and reduced mucosal edema.

• Drug Classification:

  • Direct Decongestants (Topical): Oxymetazoline, Xylometazoline. (Dose: 2-3 drops BD/TDS).

  • Indirect Decongestants: Ephedrine (displace NA from vesicles).

  • Mixed Action: Pseudoephedrine (often found in Zyrtec-D or Fedac).

• Adverse Effects:

  • Topical: Burning, stinging, and Rhinitis Medicamentosa (rebound congestion if used $\ge 5$ days).

  • Systemic (Pseudoephedrine): Cardiovascular stimulation (elevated BP, tachycardia, palpitations) and CNS stimulation (anxiety, insomnia, restlessness). Clinical tip: Avoid use close to bedtime.

• Drug Interactions and Contraindications:

  • MAO Inhibitors (MAOi): Prevents NA breakdown. Combining with Pseudoephedrine can lead to uncontrolled hypertension and urinary retention.

  • Contraindications: Severe HTN, Heart disease, Hyperthyroidism, and Glaucoma.

LTRA and Intranasal Corticosteroids

• Montelukast (LTRA):

  • Antagonizes Leukotriene (LT) receptors derived from arachidonic acid.

  • Dose: $10\,\text{mg}$ QD.

  • Adverse Effects: Mild (headache, GI discomfort). Rare but serious: Mood changes and increased risk of suicidal thoughts.

• Intranasal Corticosteroids (CS):

  • Minimizes swelling and reduces inflammatory cell infiltration and capillary permeability.

  • Examples: Nasonex (Mometasone Furoate $0.05\%$) - 2 sprays QD; Avamys (Fluticasone Furoate $27.5\,\text{mcg/spray}$).

  • Cautions: Discard 2 months after opening. Avoid abrupt discontinuation if used long-term to prevent withdrawal symptoms.

Pharyngitis and Cough Management

• Pharyngitis:

  • Inflammation of the pharynx (viral "sore throat" or bacterial "strep throat"). S/Sx include lymphoid patches and redness.

  • Benzydamine (Difflam): Anti-inflammatory. Lozenge dose: 1 Q1-2H PRN (Max $12$); Gargle: $15\,\text{mL}$ Q3H PRN. Side effects include oral numbness or stinging.

  • Lysozyme (Leftose): Natural enzybiotic. Dose: $30\,\text{mg}$ tablets, 2-3 TDS PRN (Max $270\,\text{mg/day}$). Contraindicated in egg allergy.

  • Benzocaine (Dorithricin): Local anesthetic. Dose: 1 Q4-6H PRN. Rare risk: Methemoglobinemia.

  • Dequalinium: Quaternary ammonium compound; disrupts pathogen membrane permeability. Dose: 1 lozenge Q2-3H PRN.

• Cough:

  • Types: Dry (irritative) vs. Wet (productive/chesty with phlegm).

  • Dextromethorphan (Antitussive): Weak opioid agonist acting on the medulla. Dose: $15\,\text{mg}$ Q4-6H (Max $120\,\text{mg/day}$).

  • Guaifenesin (Expectorant): Loosens secretions. Dose: $200 - 400\,\text{mg}$ Q4H PRN (Max $2.4\,\text{g/day}$).

  • Acetylcysteine (Mucolytic): Disrupts disulfide ($S-S$) bonds in phlegm. Dose: $600\,\text{mg}$ OM/BD.

  • Diphenhydramine: Expectorant that also antagonizes $H_1$; used for acute ineffective productive cough. Dose: $20\,\text{mg}$ TDS/QDS PRN.