chronic suppurative otitis media

ALLERGIC RHINITIS
Allergic rhinitis is an IgE-mediated, type 1 hypersensitivity reaction in the mucous membranes of the nasal
airways. The disease is very common, affecting approximately 30% of the Western population. It can be
either seasonal (summer hayfever) or perennial (sometimes with seasonal exacerbations).
Aetiology
Allergy is a hypersensitivity reaction of tissues to certain substances called allergens. The commonest
allergens are highly soluble proteins or glycoproteins with a molecular weight in the range of 10000–40000.
Typical allergens include pollens, moulds, house dust mite (Dermatophagoides pteronyssinus and
D.forinae) and animal epithelia.
Pathogenesis
Immunoglobulin E is formed by plasma cells which are regulated by T-suppressor lymphocytes and Thelper
cells. In normal individuals this system maintains a constant function. In allergic patients the IgE Thelper
cells appear to promote overproduction at times of exposure to the allergen, or suppressor T cells
may not be functioning correctly. The IgE antibody is composed of an Fc and an Fab portion. The Fc
portion of IgE has an affinity for mast cells and basophils, which have receptors for the immunoglobulin on
their cell membrane. The Fab portion of IgE is free to combine with an allergen. The allergen is thought to
interact with two adjacent cellbound IgE antibody molecules, so forming a cross-link composed of IgEallergen-IgE.
This triggers a chain of events with the synthesis and release of arachidonic acid metabolites
(prostaglandin D, leukotrienes and other chemotactic factors) and initiates disruption of the mast cell with
degranulation of lysosomes (releasing histamine, proteases and more chemotactic factors). The effect is that
capillaries become more permeable, the ground substance viscosity is reduced by enzymes such as
hyaluronidase, eosinophils infiltrate the tissues and oedema occurs. This produces the typical features of
vascular congestion, oedema, rhinorrhoea and irritation.
Clinical features
Seasonal rhinitis usually occurs any time from early summer to early autumn depending on the specific
allergen. The patient suffers from rhinorrhoea, nasal irritation and sneezing, associated with itchy and
watering eyes. Some individuals (described as atopic) will have a strong family history of allergy or a
previous history of eczema or asthma. Long-standing cases of perennial allergy may not display all these
features, but they often have nasal obstruction due to hypertrophy of the turbinates sometimes associated