Describe allergic rhinitis with its pathophysiology and management.

Nature and Classification

• Allergic rhinitis is an IgE-mediated type I hypersensitivity inflammation of the nasal mucosa following exposure to an allergen in a sensitised individual.
• It is extremely common, affecting perhaps 20 to 30% of the population, and is a disease of the whole airway rather than of the nose alone.
• Pathophysiology proceeds in two phases, and the distinction explains why different drugs work at different times:

Clinical Features and Management

• The cardinal symptoms are the four — sneezing (paroxysmal, often in bouts), itching (of the nose, eyes, palate and throat), watery rhinorrhoea, and nasal blockage
• Itching is the symptom that best distinguishes allergic from other rhinitis, and should be asked about specifically
• Associated features — allergic conjunctivitis with itching, watering and redness; postnasal drip and cough; loss of smell; and fatigue and impaired concentration from disturbed sleep.
• Signs — a pale, bluish, boggy, oedematous inferior turbinate with clear secretion; allergic shiners (dark infraorbital discoloration from venous stasis); the DENNIE-MORGAN fold beneath the lower lid; the allergic salute, an upward rub of the nose with the palm, producing a transverse nasal crease; and mouth breathing
• Associations — the atopic triad of rhinitis, asthma and eczema. A large majority of asthmatics have rhinitis, and treating the nose improves asthma control — the "united airway" concept.
• Investigation — the diagnosis is clinical; skin prick testing, which is quick, cheap and sensitive but requires antihistamines to be stopped and carries a small risk of anaphylaxis; specific IgE (RAST), unaffected by drugs; nasal smear for eosinophils; and total IgE.
• Management proceeds in four steps:
• 1. Allergen avoidance — sensible but frequently impractical. For house dust mite: mattress and pillow covers, hot washing of bedding, removal of carpets and soft toys, and reducing humidity; for pollen: keeping windows shut, avoiding the outdoors at peak times, and washing on returning indoors; and removing a pet, which patients rarely accept
• 2. Pharmacotherapy:
• Intranasal corticosteroids are the most effective single treatment for all four symptoms including blockage — fluticasone, mometasone, budesonide. They take days to reach full effect and must be used regularly, not as required, and most treatment failure is failure of technique or adherence
• The correct technique must be taught: head slightly forward, spray with the opposite hand aiming outward toward the ipsilateral ear, and do not sniff hard. Aiming at the septum causes bleeding, crusting and perforation
• Oral antihistamines — second-generation, non-sedating agents (cetirizine, loratadine, fexofenadine) for sneezing, itching and rhinorrhoea; first-generation agents (chlorpheniramine) should be avoided because of sedation, impaired performance and anticholinergic effects
• Topical antihistamines (azelastine), which act faster; leukotriene receptor antagonists (montelukast), particularly with coexisting asthma; topical anticholinergic (ipratropium) for watery rhinorrhoea; sodium cromoglicate, safe in children and pregnancy but requiring frequent dosing; and saline irrigation, which is cheap and genuinely useful
• Short courses of oral steroid for severe exacerbations; depot injections should not be used
• Topical decongestants may be used for a few days only, to open the nose so that a steroid spray can reach the mucosa — and never beyond 5 to 7 days.
• 3. Immunotherapy — subcutaneous or sublingual desensitisation, which is the only treatment that alters the natural history of the disease. It is indicated where symptoms are severe, a single or few allergens are demonstrated, and medical treatment has failed; requires 3 to 5 years; and carries a small risk of anaphylaxis, so subcutaneous therapy is given only where resuscitation facilities are available
• 4. Surgery has a limited and specific role — it does not treat the allergy, and is used only to correct anatomical obstruction that prevents medical treatment from working: turbinate reduction for irreversible hypertrophy, and septoplasty for a significant deviation
• Itching is what distinguishes allergic rhinitis from other forms, and should be asked about specifically
• The early phase is histamine and the late phase is cellular, which is why blockage needs a steroid rather than an antihistamine