Adult bronchiolitis overview

# Overview
Bronchiolitis was first described by the university of Minnesota in 1899, however, in 1900, Dr. Lange, a German physician described precise pathology and possible etiologies in two of his patients and therefore, established bronchiolitis as a separate pathological entity. Adult bronchiolitis may be classified according to clinical syndromes and histological abnormalities into 6 subtypes: bronchiolitis obliterans, respiratory bronchiolitis, follicular bronchiolitis, proliferative bronchiolitis, airway-centered interstitial fibrosis, and diffuse panbronchiolitis. The pathogenesis of adult bronchiolitis is to be the result of inflammation and immunological responses that cause cellular injury and damage. Eventually, respiratory compromise results, which may be irreversible and fatal. Associated conditions include asthma and primary immunodeficiencies. The gross pathology of bronchiolitis includes bronchiolar and airway destruction. Microscopically, fibroblasts and lymphocytes are noted.Common causes of bronchiolitis include inhalational injury, viral, and drug induced, such as, mineral dusts, diacetyl, RSV and busulfan. The incidence for adult bronchiolitis is not well recorded, it is estimated that in the USA 3 per 100,000 of all community acquired pneumonias have underlying bronchiolitis. The prevalence of adult-onset bronchiolitis is unknown. The most common cause of bronchiolitis in adults is RSV, most adults tend to be asymptomatic or carriers and therefore, prevalence is difficult to stipulate. The attack rate for death caused by bronchiolitis complicated by pneumonia in elderly homes is approximately 3 per 100,000. The incidence of adult bronchiolitis increases with age; the median age at diagnosis is 68 years. There is no racial predilection in adults. Men are more commonly affected by bronchiolitis than women, and tend to have higher mortality rates. Diffuse panbronchiolitis is a common disease that tends to affect Japan. Those of Hispanic, Native American and Alaskan origins tend to have a higher likelihood of hospitalization. Developed and developing countries tend to have similar incidence, hospitalisation and mortality rates. Risk factors in the development of adult bronchiolitis include smoking, cardiovascular disease, respiratory disease, immunodeficiency and immunosuppression. If left untreated, patients with adult bronchiolitis may progress to develop cough, wheezing, and dyspnea. Common complications of adult bronchiolitis include chronic bronchitis, pneumonia, and death. Prognosis is generally excellent if viral in origin with full recovery upon completion of treatment. However, occupational bronchiolitis tends to be irreversible and permanent. There is no single diagnostic study of choice for the diagnosis of adult bronchiolitis, the gold standard for diagnosis of adult bronchiolitis is clinical assessment. However, pulmonary function testing, high resolution computed tomography (HRCT), and bronchoscopy may be useful in the diagnosis of adult bronchiolitis.A positive history of insidious onset of cough, wheezing and dyspnea with deteriorating pulmonary function is suggestive of adult bronchiolitis. The most common symptoms of adult bronchiolitis include cough, wheeze and shortness of breath. Less common symptoms of adult bronchiolitis include hemoptysis, dehydration and loss of appetite. Patients with adult bronchiolitis usually appear lethargic. Physical examination of patients with adult bronchiolitis is usually remarkable for bilateral basilar lung crackles, tachypnea, wheezing and sometimes, a low grade fever.There are no diagnostic laboratory findings associated with adult bronchiolitis. However, the following laboratory investigations may be helpful in the diagnosis of adult bronchiolitis, complete blood count, white blood cell count, C-reactive protein, blood culture, rapid viral antigen testing, arterial blood gases, pulse oximetry, urine analysis, sputum analysis, CSF analysis and culture. High resolution chest CT scan may be helpful in the diagnosis of adult bronchiolitis. Findings on CT scan suggestive of adult bronchiolitis include mosaic or diffuse air trapping, bronchial wall thickening, linear opacities, centrilobular nodules, and bronchiectasis (dilated airways). Oxygen-sensitive 3He-MRI in useful in bronchiolitis obliterans syndrome after lung or heart or kidney transplantation. Normal grafts have a higher oxygen distribution than those grafts with bronchiolitis obliterans syndrome (BOS). There are no MRI findings associated with adult bronchiolitis. Other diagnostic studies for adult bronchiolitis include lung biopsy, which rules out other causes of dyspnea and can confirm bronchiolitis obliterans syndrome, and histopathology, which demonstrates abnormalities in the walls of membranous or respiratory bronchioles, tubular narrowing or total obliteration of the lumen, concentric T lymphocyte infiltration, smooth muscle hypertrophy in the small airways, bronchiolectasia with mucus plugging, and fibrosis and scarring. The optimal medical therapy for adult bronchiolitis is unknown. Therapy is mainly the cessation of exposure to irritant agent. Bronchiolitis is treated based on severity, however, the disease is progressive and inevitably, leads to respiratory failure. Therefore, supportive therapy includes supplemental oxygen, bronchodilators, cough suppressant, anti-reflux therapy, macrolides, immunosuppressants and glucocorticoids. Bronchodilators and glucocorticoids have been heavily criticized in their role of improving symptoms, and are reserved only in those who show clinical improvement. Lung transplant is not the first-line treatment option for patients with adult bronchiolitis. Surgery is usually reserved for patients with untreatable and advanced stage lung disease.Effective measures for the primary prevention of adult bronchiolitis include the cessation of exposure to inhalants, prevention of smoking, vaping and smoking cessation, health awareness, and routine surveillance. Treating comorbidities and also reducing exposure through the use of medical masks and respirators, robots, isolation of harmful processes, ventilation, limiting exposure hours, maintenance of dust control systems, and the use of warning signs.

# Historical Perspective
Bronchiolitis was first described by the university of Minnesota in 1899, however, in 1900, Dr. Lange, a German physician described precise pathology and possible etiologies in two of his patients and therefore, established bronchiolitis as a separate pathological entity. In 1904, an association between bronchiolitis and several risk factors were made. Later in the 1980s, bronchiolitis obliterans syndrome was identified as a complication of organ transplants. In 1983, the classification of adult bronchiolitis was expanded by the addition of diffuse panbronchiolitis. Recently, workers in popcorn factories and individuals that vape have been diagnosed with popcorn lung disease (bronchiolitis obliterans, a subtype of adult bronchiolitis).

# Classification
Adult bronchiolitis may be classified according to clinical syndromes and histological abnormalities into 6 subtypes: bronchiolitis obliterans, respiratory bronchiolitis, follicular bronchiolitis, proliferative bronchiolitis, airway-centered interstitial fibrosis, and diffuse panbronchiolitis.

# Pathophysiology
The pathogenesis of adult bronchiolitis is to be the result of inflammation and immunological responses that cause cellular injury and damage. Eventually, respiratory compromise results, which may be irreversible and fatal. Associated conditions include asthma and primary immunodeficiencies. The gross pathology of bronchiolitis includes bronchiolar and airway destruction. Microscopically, fibroblasts and lymphocytes are noted.

# Causes
Common causes of bronchiolitis include inhalational injury, viral, and drug induced, such as, mineral dusts, diacetyl, RSV and busulfan. Less common causes include heart/lung/kidney transplant, rheumatoid arthritis and ulcerative colitis.

# Differentiating Hereditary pancreatitis from Other Diseases

# Epidemiology and Demographics
The incidence for adult bronchiolitis is not well recorded, it is estimated that in the USA 3 per 100,000 of all community acquired pneumonias have underlying bronchiolitis. The prevalence of adult-onset bronchiolitis is unknown. The most common cause of bronchiolitis in adults is RSV, most adults tend to be asymptomatic or carriers and therefore, prevalence is difficult to stipulate. The attack rate for death caused by bronchiolitis complicated by pneumonia in elderly homes is approximately 3 per 100,000. The incidence of adult bronchiolitis increases with age; the median age at diagnosis is 68 years. There is no racial predilection in adults. Men are more commonly affected by bronchiolitis than women, and tend to have higher mortality rates. Diffuse panbronchiolitis is a common disease that tends to affect Japan. Those of Hispanic, Native American and Alaskan origins tend to have a higher likelihood of hospitalization. Developed and developing countries tend to have similar incidence, hospitalisation and mortality rates.

# Risk Factors
Risk factors in the development of adult bronchiolitis include smoking, cardiovascular disease, respiratory disease, immunodeficiency and immunosuppression.

# Screening
There is insufficient evidence to recommend routine screening for adult bronchiolitis.

# Natural History, Complications, and Prognosis
If left untreated, patients with adult bronchiolitis may progress to develop cough, wheezing, and dyspnea. Common complications of adult bronchiolitis include chronic bronchitis, pneumonia, and death. Prognosis is generally excellent if viral in origin with full recovery upon completion of treatment. However, occupational bronchiolitis tends to be irreversible and permanent.

# Diagnosis

## Diagnostic Study of Choice
There is no single diagnostic study of choice for the diagnosis of adult bronchiolitis, the gold standard for diagnosis of adult bronchiolitis is clinical assessment. However, pulmonary function testing, high resolution computed tomography (HRCT), and bronchoscopy may be useful in the diagnosis of adult bronchiolitis.

## History and Symptoms
A positive history of insidious onset of cough, wheezing and dyspnea with deteriorating pulmonary function is suggestive of adult bronchiolitis. The most common symptoms of adult bronchiolitis include cough, wheeze and shortness of breath. Less common symptoms of adult bronchiolitis include hemoptysis, dehydration and loss of appetite.

## Physical Examination
Patients with adult bronchiolitis usually appear lethargic. Physical examination of patients with adult bronchiolitis is usually remarkable for bilateral basilar lung crackles, tachypnea, wheezing and sometimes, a low grade fever.

## Laboratory Findings
There are no diagnostic laboratory findings associated with adult bronchiolitis. However, the following laboratory investigations may be helpful in the diagnosis of adult bronchiolitis, complete blood count, white blood cell count, C-reactive protein, blood culture, rapid viral antigen testing, arterial blood gases, pulse oximetry, urine analysis, sputum analysis, CSF analysis and culture.

## Electrocardiogram
There are no ECG findings associated with adult bronchiolitis.

## X-ray
An x-ray may be helpful to rule out diagnoses other than adult bronchiolitis. Findings on an x-ray may include congenital abnormalities, lobar pneumonia, congestive heart failure, and foreign body aspiration. X - ray  findings for adult bronchiolitis are non-specific but may include, hyperinflation, lobar infiltrates, and atelectasis.

## Echocardiography and Ultrasound
There are no echocardiography associated with adult bronchiolitis. Ultrasound may be helpful in the diagnosis of adult bronchiolitis. Findings on an ultrasound suggestive of adult bronchiolitis include aberrant lung pattern and subpleural consolidations.

## CT scan
High resolution chest CT scan may be helpful in the diagnosis of adult bronchiolitis. Findings on CT scan suggestive of adult bronchiolitis include mosaic or diffuse air trapping, bronchial wall thickening, linear opacities, centrilobular nodules, and bronchiectasis (dilated airways).

## MRI
Oxygen-sensitive 3He-MRI in useful in bronchiolitis obliterans syndrome after lung or heart or kidney transplantation. Normal grafts have a higher oxygen distribution than those grafts with bronchiolitis obliterans syndrome (BOS). There are no MRI findings associated with adult bronchiolitis.

## Other Imaging Findings
There are no other imaging findings associated with adult bronchiolitis.

## Other Diagnostic Studies
Other diagnostic studies for adult bronchiolitis include lung biopsy, which rules out other causes of dyspnea and can confirm bronchiolitis obliterans syndrome, and histopathology, which demonstrates abnormalities in the walls of membranous or respiratory bronchioles, tubular narrowing or total obliteration of the lumen, concentric T lymphocyte infiltration, smooth muscle hypertrophy in the small airways, bronchiolectasia with mucus plugging, and fibrosis and scarring.

# Treatment

## Medical Therapy
The optimal medical therapy for adult bronchiolitis is unknown. Therapy is mainly the cessation of exposure to irritant agent. Bronchiolitis is treated based on severity, however, the disease is progressive and inevitably, leads to respiratory failure. Therefore, supportive therapy includes supplemental oxygen, bronchodilators, cough suppressant, anti-reflux therapy, macrolides, immunosuppressants and glucocorticoids. Bronchodilators and glucocorticoids have been heavily criticized in their role of improving symptoms, and are reserved only in those who show clinical improvement.

## Surgery
Lung transplant is not the first-line treatment option for patients with adult bronchiolitis. Surgery is usually reserved for patients with untreatable and advanced stage lung disease.

## Primary Prevention
Effective measures for the primary prevention of adult bronchiolitis include the cessation of exposure to inhalants, prevention of smoking, vaping and smoking cessation, health awareness, and routine surveillance. Treating comorbidities and also reducing exposure through the use of medical masks and respirators, robots, isolation of harmful processes, ventilation, limiting exposure hours, maintenance of dust control systems, and the use of warning signs.

## Secondary Prevention
There are no established measures for the secondary prevention of adult bronchiolitis.