Allergic Rhinitis

Allergic Rhinitis


ALLERGIC RHINITIS

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 
  1. Histamine (most important)
  2. PAF
  3. Heparin
  4. Cytokines (IL-1, 3, 4, 5, 6; INF)
  5. Leukotriens (B4, Ch D4)
  6. Eosinophil chemolactic factor (ECF)
  7. PGD2
  8. Neutrophil chemolactic factor (NCF)

The release of these mediators result in : –

  1. Increased vascular permeability and vasodilatation which result in tissue edema – Nasal blockage and sneezing.
  2. Smooth muscle spasm → Bronchoconstriction
  3. Hyperactivity of glands → Rhinorrhea
  4. 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

Symptoms:

  • 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.
  • Anosmia,Headache.
  • It does not lead to Epistaxis.

Signs:

  • 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 .
Exam Question
 
  • 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.
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