PATHOGENESIS OF ALLERGIC RHINITIS
- Allergic rhinitis is a type I hypersensitivity. It occurs in two phases:
1. Initial response/Acute or early phase
- Antigen specific Ig E antibodies bind to the surface receptors of mast cells and basophils.
- The process from first antigen exposure to the coating of mast cells by Ig E acts as sensitization (prior sensitization), called priming or sensitizing exposure (dose).
- Subsequent exposure (shocking dose) to same antigen then results in activation of mast cells and basophils with release of inflammatory mediators
- Histamine (most important)
- Cytokines (IL-1, 3, 4, 5, 6; INF)
- Leukotriens (B4, Ch D4)
- Eosinophil chemolactic factor (ECF)
- Neutrophil chemolactic factor (NCF)
The release of these mediators result in : –
- Increased vascular permeability and vasodilatation which result in tissue edema – Nasal blockage and sneezing.
- Smooth muscle spasm → Bronchoconstriction
- Hyperactivity of glands → Rhinorrhea
- Recruitment of inflammatory cells.
2. Late phase response
- Recruited inflammatory cells of initial phase amplify and sustain the inflammatory response without additional exposure to the triggered antigen.
- PAF is the most important mediator in initiation of late phase response.
- Eosinophils are particularly important cells among the recruited cells which also include neutrophils, basophils, monocytes and T-cells.
- It causes symptoms like nasal congestion and post nasal drip.
CLINICAL TYPES OF ALLERGIC RHINITIS
- Seasonal:Hay fever due to pollen grains that occur at the time of pollination season.
- Perennial:It affects the patient throughout the year.
CLINICAL FEATURES OF ALLERGIC RHINITIS
- Itching in the eyes and nose.
- Watery discharge from the eyes and nose.
- Allergic Rhinits is a most common cause of Nasal Discharge.
- Paroxysmal Sneezing
- Nasal Obstruction-may lead to Rhinolalia Clausa.
- It does not lead to Epistaxis.
- Nasal Mucosa appears pale and swollen.
- Allergic Salute:Itching in the nose and rhinorrhea may lead the patient to lift the tip of his nose upwards with his palm which appears like a salute.
- Darrier’s Line:Repeated allergic salute may result in a horizontal line on the nasal dorsum a little superior to the tip of the nsoe.
INVESTIGATIONS IN A CASE OF ALLERGIC RHINITIS
- Immediate hypersensitive skin test : Most valuable tool for identifying the causative antigen in Allergic Rhinitis.
- The radioallergosorbent test (RAST):Though accurate, is more expensive and less discriminative than skin testing.
- Elevated immunoglobulin E (IgE) levels :Observed in only 30%-40% of patients with allergic rhinitis and may be secondary to other unrelated disorders.
- Although eosinophils are usually identified in nasal secretions from patients with allergic rhinitis, they are also detected in eosinophilic nonallergic rhinitis and hyperplastic sinusitis.
- Eosinophil count:peripheral eosinophilia seen in a peripheral blood smear is an inconsistent finding.
TREATMENT IN A CASE OF ALLERGIC RHINITIS
- Avoidance of Allergens.
- Medications:Antihistaminic,Steroids(generally Nasal Steroids is used.Systemic steroids in case of Severe Allergic Rhinitis),Leukotriene Antagonist like Montelukast.
- Immunotherapy:Specific desensitization against known Allergens.
- Surgery: done in a case of allergic rhinitis when other methods have failed or when there is marked septal deviation or bony turbinate enlargement which makes topical nasal spray usage difficult.
- Radiofrequency ablation/Laser ablation of the inferior turbinate or Inferior turbinectomy.
- It should never be used as first line of treatment.
DIFFERENTIAL DIAGNOSIS OF ALLERGIC RHINITIS
- Vasomotor Rhinitis:Imbalance of Autonomic Nervous System is considered to be the cause.Sneezing is less.but blocking and rhinorrhoea dominate.Vidian Neurectomy may help.
- Churg-Strauss syndrome:Allergic rhinitis is associated with peripheral eosinophilia, cutaneous purpura, mononeuritis, asthma and small-vessel vasculitis .
- Immediate hypersensitivity skin test is most useful in diagnosis of allergic rhinitis.
- When small-vessel vasculitis is associated with peripheral eosinophilia, cutaneous purpura, mononeuritis, asthma, and allergic rhinitis, a diagnosis of Churg-Strauss syndrome is considered.
- Rhinolalia Clausa may be associated with Allergic Rhinitis.
- Early mediators of allergic rhinitis are Leukotriene,IL-4 ,IL-5.
- In Allergic rhinitis nasal mucosa is Pale and swollen.
- Surgical procedure like Radiofrequency ablation/Laser ablation of the inferior turbinate or Inferior turbinectomy may be done in a case of Allergic Rhinitis.
- Treatment of Allergic Rhinits includes avoiding allergen,corticosteroids,surgery.
- Allergic Rhinitis does not leads to Epistaxis.
- Most common cause of Nasal Discharge is Allergic Rhinitis.
- Histamine is a preformed toxin involved in mechanism of allergic rhinitis.
- Allergic rhinitis is a type 1 hypersensitivity reaction.
- Allergic salute is seen in Allergic Rhinitis.