The term “rhinitis” is used to describe nasal inflammation that results in rhinorrhea (colloquially known as “runny nose”), congestion, nasal itch, sneezing, postnasal drainage, and in some patients, ocular symptoms such as watering eyes. It represents one of the most frequently encountered chronic conditions for which medical care is sought.
Studies conducted in the United States and United Kingdom have shown that the prevalence of allergic rhinitis is between 24 and 28%, accounting for approximately 3% of all physician visits. The direct and indirect costs just for this type of rhinitis exceed 10 billion American dollars, though non-allergic rhinitis also results in a significant economic burden.
Albeit this condition alone is never life-threatening, its impact on quality of life and both work and school productivity can be substantial. Furthermore, rhinitis can aggravate other chronic conditions such as otitis, sinusitis, and asthma – all of which have significant morbidity.
Pathophysiology of the condition
The nose and nasal cavities have several important functions; first and foremost, their role is to provide an airway, which is pivotal for the senses of smell and taste. The nasal passages also act as filters, protecting the lungs from noxious stimuli in the environment. In addition, the large surface area of the mucosa covered turbinates warm and humidify air prior to entry into the lungs.
When airflow is seriously inhibited, all of the aforementioned functions can be adversely affected. In rhinitis, which is usually caused by an increase in histamin levels, a combination of the inflammation of nasal mucosa and increased mucus production can lead to such airflow obstruction.
Rhinitis can be induced by allergic stimuli, non-allergic triggers or both (which is known as mixed rhinitis). Allergic rhinitis only occurs in patients with a genetic predisposition to developing allergies. In short, it represents an inflammatory condition of the nasal mucosa, mediated by an IgE-associated response to indoor or outdoor environmental allergens.
The underlying mechanisms leading to non-allergic rhinitis are quite variable and less well understood. Vasomotor rhinitis is a non-immunologic syndrome of nasal mucosal vascular engorgement triggered by environmental conditions (cold air, humidity, barometric pressure, strong smells and emotions). The most common cause of medication-induced rhinitis is overuse of certain topical nasal decongestants.
Anatomic anomalies can also contribute to non-allergic types of rhintis. Both adenoid and turbinate hypertrophy can result in chronic nasal congestion with little relief from medications. Atrophic rhinitis is usually observed in patients who have had overzealous surgeries, where too much mucus-secreting tissues are removed.
All types of rhinitis can be associated with co-morbidities and secondary complications. Rhinitic mucosal inflammation can contribute to the development of acute and chronic sinusitis, Eustachian tube dysfunction and chronic otitis media. These disorders can subsequently lead to speech delay in pediatric populations and (in rare instances) permanent hearing damage.
It must be noted that nasal congestion is commonly observed in pregnancy, even in some points of the menstrual cycle. This is linked to the high levels of progesterone, which causes smooth muscle relaxation in blood vessels, pooling of the blood in the venous sinusoids and chronic nasal obstruction.
Establishing a diagnosis
A thorough history and physical examination are the cornerstones of establishing the precise diagnosis. Even though some rhinitis medications are efficacious in the treatment of all types of rhinitis, it benefits the patient to have a specific diagnosis. For that purpose, physicians make use of a myriad of historical clues and subtle differences on physical exam, coupled with allergen skin testing.
The nature of symptoms often differs between two main types of rhinitis (i.e. allergic and non-allergic). Patients with allergic rhinitis present with significant sneezing and nasal itch, and often have troublesome ocular symptoms. On the other hand, patients with non-allergic rhinitis typically have symptoms that involve only the nose (primarily nasal congestion) without significant pruritus or sneezing.
Subtle differences are also observed on physical examination. In allergic rhinitis, nasal mucosa is classically boggy, edematous and often with a blue-white hue. The nasal examination in non-allergic rhinitis depends on the underlying cause of the disorder; mucosa can appear normal with increased clear watery secretions, but it also may be erythematous or even atrophic.
Skin-prick testing with a set of allergens is considered the primary method for identifying specific triggers of allergic rhinitis. An alternative procedure is the use of allergen-specific IgE tests (such as radioallergosorbent tests) which provide an in vitro measure of a patient’s specific IgE levels against particular allergens. Nasal provocation test is an in vivo diagnostic method that mimics the allergen natural exposure.