The nasal cavity consists of a number of structures, the function of which is to warm and humidify the air as well as filter large particles and prevent them from entering the lower airways. The lining of the nose is a richly innervated and vascular structure. The production of nasal mucous together with cilial function results in the swallowing of mucous with entrapped particles. The sinuses within the skull drain into the nasal passages through small orifices, of the order of the diameter of a pin head. The function of the sinuses is uncertain, but may serve as a reservoir of protective mucous, may dampen sudden pressure changes within the nasal cavity during respiration and swallowing, and decreases the weight of the skull. The eustachian tube links the middle ear to the nasopharynx. Age, anatomical abnormalities, infection or allergic inflammation can all serve to alter its function and predispose patients to recurrent infection and (at times) impaired hearing.
The integrity of the nasal and sinus mucosa and protection from infection is maintained by a combination of anatomical factors, adequate cilial function, normality of mucous secretions, the presence of antibody (both secreted and transudated), antibacterial substances within the nasal secretions, as well as other components of the cellular immune system within the mucosa. These components include T & B lymphocytes as well as plasma cells capable of secreting antibody onto the mucosal surface.
The allergic arm of the immune system is designed to kill worms and parasites. Some genetically predisposed individuals, however, develop immune responses to non-toxic environmental factors such as pollens, dust mite, molds and tree pollens. To a large extent, this is dependent on genetic predisposition, but exposure is also important, perhaps at critical times during life. One needs to be exposed to allergen in order to develop an allergic response, resulting in sensitization. The subsequent development of symptoms is then dependent on the occurrence and level of re-exposure. There are two phases to the allergic response. The initial or immediate response involves cross-linking of IgE molecules on the surface of mast cells resulting in their degranulation, and the release of histamine as well as other vaso-active substances. Within the nasal cavity, this often results in sneezing, irritation, acute rhinorrhoea and nasal congestion. There is also a late phase response, which involves recruitment of additional cells into the nasal cavity resulting in the chronic bogginess and swelling of the nose characteristic of chronic rhinitis.
Allergic rhinitis is relatively common, occurring in up to 8% of the population at any one time. It is more common in males than females, and more common in households where smoking occurs. The prevalence is greatest between the ages of 5 - 25, and thereafter decreases with increasing age. In patients with allergic rhinitis, common allergens include dust mite derived protein, grass pollens as well as molds and animal danders. Not all patients with rhinitis, however, are allergic. Around 10 - 20% of patients complaining of chronic rhinorrhoea or congestion do not have any evidence of allergic disease, a condition known as non-allergic rhinitis. Whereas allergic rhinitis may be treated in a number of ways including allergen avoidance, antihistamines, nasal steroids and desensitization, non-allergic rhinitis is generally more difficult to treat satisfactorily. Dietetic manipulation and "elimination diets" play a very limited role in the management of rhinitis, the mechanism of which has much to do with the biochemistry of food, and little to do with the immune system or "allergy".
A common source of concern is the possible influence of allergic disease on the occurrence of recurrent sinus or middle ear infections. Sinusitis is quite common (particularly in young children), who may experience anywhere between 6 - 8 upper respiratory infections per year, and even more commonly if they are in child care. Around 10% of these infections will be followed by sinusitis, of which half will resolve spontaneously without antibiotics. Whilst immunodeficiency is often considered in the differential diagnosis of recurrent sinusitis, these conditions are relatively rare and are unlikely with recurrent sinusitis or recurrent otitis media alone. More common contributing factors are those of anatomical abnormalities (such as nasal polyps) which impair sinus drainage, or allergic rhinitis (which may occlude the sinus ostia). Contrary to popular belief, nasal polyps are not necessarily the result of allergy. Indeed polyps are no more common in the allergic than the non-allergic population.
Otitis media is a common affliction of childhood, the majority of whom will have had at least one infection by the age of 2 years with up to 17% having 3 or more episodes over a 6 month period. This is not only a source of distress for patient and parent alike, but the long term consequences of recurrent infection or chronic serous infusion leading to hearing impairment are of concern. The eustachian tube links the nasopharynx to the middle ear. Under normal circumstances, the eustachian tube maintains near ambient pressure in the middle ear cavity by opening and closing such as with swallowing, or yawning.
Eustachian tube dysfunction however, may impair this resulting in the development of negative pressure within the middle ear cavity, with retrograde aspiration of potentially infectious nasopharyngeal contents into the middle ear cavity resulting in infection, or alternatively negative pressure resulting in chronic serous effusions. The mechanical obstruction of the eustachian tube may result from oedema around the eustachian tube opening (such as with infection or allergic inflammation), or by extrinsic compression of the eustachian tube by enlarged adenoids. Young children may also have a functional obstruction due to impaired tensor veli palatini muscle function, as well as sub optimal stiffness of the cartilage support of the eustachian tube. Furthermore, the eustachian tube may be continually reseeded with bacteria by chronically infected adenoids.
Correction of anatomical abnormalities (such
as removal of nasal polyps or removal of hypertrophied adenoids),
aggressive treatment of infection as well as allergic upper airways
disease are often important strategies in the adequate control
of recurrent sinusitis and middle ear infections.
