Eosinophilic bronchitis (EB) is a type of airway inflammation due to excessive

mast cell A mast cell (also known as a mastocyte or a labrocyte) is a resident cell of connective tissue that contains many granules rich in histamine and heparin. Specifically, it is a type of granulocyte derived from the myeloid stem cell that is a par ...

recruitment and activation in the superficial airways as opposed to the smooth muscles of the airways as seen in

asthma Asthma is a long-term inflammatory disease of the airways of the lungs. It is characterized by variable and recurring symptoms, reversible airflow obstruction, and easily triggered bronchospasms. Symptoms include episodes of wheezing, co ...

. It often results in a chronic

cough A cough is a sudden expulsion of air through the large breathing passages that can help clear them of fluids, irritants, foreign particles and microbes. As a protective reflex, coughing can be repetitive with the cough reflex following three ph ...

Lung function tests Pulmonary function testing (PFT) is a complete evaluation of the respiratory system including patient history, physical examinations, and tests of pulmonary function. The primary purpose of pulmonary function testing is to identify the severity ...

are usually normal. Inhaled corticosteroids are often an effective treatment.

Signs and symptoms

The most common symptom of eosinophilic bronchitis is a chronic dry cough lasting more than 6–8 weeks. Eosinophilic bronchitis is also defined by the increased number of

eosinophil Eosinophils, sometimes called eosinophiles or, less commonly, acidophils, are a variety of white blood cells (WBCs) and one of the immune system components responsible for combating multicellular parasites and certain infections in vertebrates. A ...

s, a type of white blood cell, in the sputum compared to that of healthy people. As patients with asthma usually present with eosinophils in the sputum as well, some literature distinguish the two by classifying the condition as non-asthmatic eosinophilic bronchitis (NAEB) versus eosinophilic bronchitis in asthma. Non-asthmatic eosinophilic bronchitis is different from asthma in that it does not have airflow obstruction or airway hyperresponsiveness. Along with eosinophils, the number of

s, another type of white blood cell, is also significantly increased in the bronchial wash fluid of eosinophilic bronchitis patients compared to asthmatic patients and other healthy people. Asthmatic patients, however, have greater number of mast cells that go into the smooth muscle of the airway, distinguishing it from non-asthmatic eosinophilic bronchitis. The increased number of mast cells in the smooth muscle correlate with the increased hyperresponsiveness of the airway seen in asthma patients, and the difference in the mast cell infiltration of the smooth muscle may explain why eosinophilic bronchitis patients do not have airway hyperresponsiveness. Eosinophilic bronchitis has also been linked to other conditions such as

COPD Chronic obstructive pulmonary disease (COPD) is a type of progressive lung disease characterized by long-term respiratory symptoms and airflow limitation. The main symptoms include shortness of breath and a cough, which may or may not produce ...

atopic Atopy is the tendency to produce an exaggerated immunoglobulin E (IgE) immune response to otherwise harmless substances in the environment. Allergic diseases are clinical manifestations of such inappropriate, atopic responses. Atopy may have a ...

cough, and

allergic rhinitis Allergic rhinitis, of which the seasonal type is called hay fever, is a type of inflammation in the nose that occurs when the immune system overreacts to allergens in the air. Signs and symptoms include a runny or stuffy nose, sneezing, red, i ...

Pathophysiology

The number of eosinophils in the sputum samples of non-asthmatic eosinophilic bronchitis patients are similar to those of patients with asthma. In the sputum samples of those with NAEB,

histamine Histamine is an organic nitrogenous compound involved in local immune responses, as well as regulating physiological functions in the gut and acting as a neurotransmitter for the brain, spinal cord, and uterus. Since histamine was discovered ...

and prostaglandin D2 is increased. This suggests that the superficial airways have significant mast cell activation and this may lead to the differing symptom presentation compared to asthma. Inflammation caused by eosinophils is associated with an increased cough reflex. In another study, however, some follow-up patients who were asymptomatic also had increased eosinophils in their sputum, indicating that the inflammation is not always associated with an increased cough reflex. The cause of the inflammation can be associated with environmental triggers or common allergens such as dust, chloramine, latex, or welding fumes.

Diagnosis

Diagnosis of eosinophilic bronchitis is not common as it requires the examination of the patient's sputum for a definitive diagnosis, which can be difficult in those who present with a dry cough. In order to induce the sputum, the patient has to inhale increasing concentrations of

hypertonic In chemical biology, tonicity is a measure of the effective osmotic pressure gradient; the water potential of two solutions separated by a partially-permeable cell membrane. Tonicity depends on the relative concentration of selective membrane- ...

saline solution. If this is unavailable, a bronchoalveolar lavage can be done, and the bronchial wash fluid can be examined for eosinophils. The diagnosis is usually considered later by ruling out other life-threatening conditions or more common diagnoses such as asthma and

GERD Gerd or GERD may refer to: * Gerd (given name), a list of people with the given name or nickname * Gerd (moon), a moon of Saturn * Gerd Island, South Orkney Islands, Antarctica * Gastroesophageal reflux disease, a chronic symptom of mucosal damage ...

, and by seeing an improvement in symptoms with inhaled corticosteroid treatment. Chest X-rays and lung function tests are usually normal. CT scans may show some diffuse airway wall thickening.

Management

If the patient has a known allergen or trigger for the eosinophilic bronchitis, the recommended treatment is to avoid the triggers. If the cause of the eosinophilic bronchitis is unknown, the first line treatment is inhaled corticosteroids. Patients respond well to inhaled corticosteroids and their eosinophil counts in their sputum usually decrease after treatment. There has not been a study to determine the ideal dosage of inhaled corticosteroids for patients with eosinophilic bronchitis, and there is no consensus on whether the treatment should be discontinued once the patient's symptoms resolve or to continue long-term. The use of oral corticosteroids for eosinophilic bronchitis is rare, but it may be considered when inhaled corticosteroids are ineffective in managing the symptoms.

Epidemiology

Approximately 10–30% of people who present with a chronic cough are suspected to be symptomatic due to eosinophilic bronchitis.

References

{{reflist Bronchus disorders