Rhinitis overview

# Overview
Rhinitis is a heterogenous disorder that is often treated with triviality. It is a highly prevalent, global disease that can have significant impact on the quality of life of affected individuals. Rhinitis is characterized by the presence of one or more nasal symptoms such as sneezing, nasal itching, rhinorrhea(anterior and posterior), and nasal congestion. There can be varying degrees of nasal inflammation. It has a huge financial impact on the society, and generates between $1.6-$4.9 billion in direct expenditure in the US annually. The estimated annual indirect cost from lost productivity in the US ranges between $0.1-$9.7 billion dollars. Chronic rhinitis is one of the most common problems seen by physicians, and allergic rhinitis is the most common type of chronic rhinitis. The prevalence of allergic rhinitis has been steadily increasing in various countries across the world. Unfortunately, rhinitis is often overlooked, underdiagnosed, undertreated, and mistreated.  An understanding of the etiology of the different types of rhinitis and the treatment modalities, would improve the quality of care offered, and ultimately improve the quality of life of those who suffer from chronic rhinitis.

# Historical Perspective
Rhinitis has been in existence since the ancient times. Seasonal allergic rhinitis (hay fever) evolved with the industrialization of westernized  countries in the 19th century, and it was a common condition in Europe and North America by the end of the 19th century. Nonallergic Rhinitis with Eosinophilic Syndrome(NARES) was first described in 1981 by Jacobs et al. Primary atrophic rhinitis has been well known for ages to the ancient Egyptians, Greeks, and Indians, and it was first described by Bernhard Fraenkel in 1876.

# Classification
Rhinitis can be broadly classified into allergic and nonallergic rhinitis. Some forms of rhinitis are not easily classified as either allergic or nonallergic, and sometimes, there also appear to be an overlap of both allergic and nonallergic rhinitis (sometimes referred to as 'mixed' rhinitis). The classification and diagnosis of nonallergic rhinitis is challenging due to its diverse etiology,  and it is also not well understood compared to the allergic type.

# Pathophysiology
Allergic rhinitis is a multifactorial disease, its development is influenced by an interplay of genetic and environmental factors. Aeroallergens in the nasal tissue undergo antigen processing, eliciting allergen-specific allergic responses and also promoting the development of allergic airway disease. Proteins and glycoproteins in indoor and outdoor inhalant allergens such as dust mite fecal particles, cockroach residues, animal danders, molds, and pollens are common aeroallergens causing allergic rhinitis. Allergic rhinitis is usually an IgE mediated disease with varying degrees of nasal inflammation. Nonallergic rhinitis is a heterogenous group with poorly defined and understood pathophysiology, and it consists of a variety of conditions which require more research and phenotyping.

# Causes
One of the most common diseases presenting to physicians is chronic rhinitis, and determination of the etiology is crucial to ensure appropriate management. Allergic rhinitis is the most common type of chronic rhinitis, and it is the fifth most common chronic ailment overall in the U.S. Allergic rhinitis is triggered by the inhalation of indoor and outdoor aeroallergens such as pollens, molds, and animal dander. Nonallergic rhinitis comprises a heterogenous group of disorders, some of which are still poorly defined and understood. Nonallergic rhinitis can be induced by non-specific triggers such as exposure to chemical odors, cigarette smoke, spicy food, exercise, and cold air.

# Differentiating Rhinitis from other Diseases
It is important to differentiate rhinitis from other conditions micmicking the symptoms of rhinitis such as intranasal foreign bodies, cerebrospinal fluid rhinorrhea, nasal polyps and tumors.

# Epidemiology and Demographics
Rhinitis is a very frequent and highly prevalent global disease.
Allergic rhinitis is estimated to affect one in every six Americans, and it is the fifth most chronic disease in the U.S. Allergic rhinitis is the most common chronic disease in the pediatric age group in the U.S, and it was the most common diagnosis reported in the 2000 Otolaryngology Workforce study. The estimated prevalence of allergic rhinitis ranges from 9-42%. Annually, between 30-60 million people in the U.S suffer from allergic rhinitis, 10-30% of these individuals are adults, and up to 40% are children.  The prevalence of allergic rhinitis has been found to be increasing in countries worldwide, and factors such as  increased airborne pollution, a rise in the population of dust mite in inadequately ventilated offices/homes with central heating/air conditioning, and sedentary lifestyles, have been suggested to contribute to the rise in its prevalence. The prevalence of allergic rhinitis has significantly increased during the past 50 years, with over 50% of adolescents in some countries reporting symptoms of allergic rhinitis.  The prevalence of allergic rhinitis was noticed to have doubled in several countries over the last two decades in studies done in children between the ages 6-14years around the globe. Nonallergic rhinitis is also very common, and it has been estimated to affect about 19 million people in the U.S. "Mixed rhinitis" is estimated to affect about 26 million individuals in the United States.

# Risk factors
Risk factors for allergic rhinitis include a history of other atopic diseases such as asthma and atopic dermatitis, and a history of rhinitis in the parent.
Some of the risk factors for infectious rhinitis are daycare attendance, young age, and exposure to air pollutants.

# Natural History, Complications and Prognosis
Allergic rhinitis rarely occurs in isolation, it is a product of a genetic predisposition, epigenetic events, and environmental exposures, and it is frequently associated with other forms of atopy such as eczema, asthma, and allergic eye disease(allergic rhinoconjunctivitis). The vast majority of individuals with asthma have rhinitis, and allergic eye disease has been reported to affect almost all patients with allergic rhinitis. Nonallergic rhinitis is also associated with asthma. Frequent extension of rhinitis (especially infectious rhinitis) into the sinuses also occur, resulting in rhinosinusitis. Children with nonallergic rhinitis have a higher likelihood of undergoing remission, compared with those with allergic rhinitis, who tend to have a more  persistent disease. Remission occurs in up to 73% of four year old children with nonallergic rhinitis by the age of eight years. Rhinitis is a significant cause of lost school and work days, and it constitutes a huge financial burden to the society. Untreated/poorly treated chronic rhinitis is associated with a diminished quality of life, disordered sleep, impaired work performance, and several other comorbidities.

# History and Symptoms
It is pertinent to obtain the history of the symptoms of rhinitis, and also ask about the symptoms that are most bothersome to the patient. The pattern of the symptoms, precipitating factors, environmental history, coexisting conditions, family history, and previous response to medications, should all be obtained.

# Physical Examination
A careful history and physical examination is essential for accurate diagnosis, treatment, and prevention of the potential complications associated with chronic rhinitis. It is essential to examine all the organ systems that are potentially affected by allergies. A detailed examination of the upper respiratory tract should be done in all patients presenting with rhinitis.

# Laboratory Findings
Allergic rhinitis can be confirmed  by recording specific IgE reactivity to relevant aeroallergens in the patient's history, via skin testing(skin-prick/intradermal test) or serum specific IgE testing known as the radioallergosorbent test(RAST).

# X ray
Chest x-ray is of no clinical importance in the diagnosis of rhinitis, unless it is necessary for the evaluation of some associated comorbid conditions.

# CT
Imaging studies such as CT scan are not routinely required for the diagnosis of rhinitis. However, a CT scan may be required when further evaluation is needed, such as in cases of complicated rhinosinusitis or when other pathological conditions are suspected. CT scans are also usually indicated for the evaluation of atrophic rhinitis.

# Other Diagnostic Studies
Nasal endoscopy is a very good technique for detecting sinonasal pathologies as well as anatomical variations that are not accessible on anterior rhinoscopy, and it should be considered in the early diagnosis of various sinonasal diseases to ensure a complete examination of the nose and sinuses.

# Medical Therapy
The etiology and severity of rhinitis often determines the type of medical therapy offered. The commonly used medications are antihistamines and corticosteroids. Avoidance of triggers when possible, and saline irrigation of the nose also has clear benefits. Allergen-specific immunotherapy is also indicated for the treatment of allergic rhinitis in appropriately selected patients.

# Surgery
Surgery is not commonly required for the management of rhinitis. Surgical procedures are however, sometimes indicated in the management of structural/mechanical problems, or coexisting comorbid conditions.