Bronchiolitis overview
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Ahmed Elsaiey, MBBCH [2]
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Overview
Bronchiolitis is the most common lower respiratory tract infection in pediatric patients between 1 month and 2 years of age. It is usually caused by the respiratory syncytial virus (RSV) and is characterized by inflamation, edema and necrosis of the bronchiole's epithelium. Typical clinical manifestations include rhinitis, cough, wheezing, respiratory rales (crackles), use of respiratory accessory muscles and/or nasal flaring.
Historical Perspective
Bronchiolitis first case reported returns back to 1899 when it was discovered by members of university of Minnesota. The disease was fully described in 1901 by Dr. Lange.[1]
Classification
Bronchiolitis is a wide ranged disease that affects the small respiratory airways (bronchioles). Bronchiolitis should be classified in order to understand how it may occur and the clinical manifestation that could be observed. It is classified based on the age and the different forms of the disease. According to age, it is classified into either adult or infants. Based on the different histological features, it can be classified into acute infectious broncholitis, bronchiolitis obliterans, proliferative bronchiolitis, diffuse panbronchiolitis and respiratory bronchiolitis.[2]Based on the Bronchiolitis Severity Score (BSS), bronchiolitis is classified into 4 classes.
Pathophysiology
Bronchiolitis is transmitted by air droplets if it is caused by RSV and that leads to infection of nasopharyngeal mucosa. After the infection, the virus will spread to the lower airway tracts till it reaches the bronchioles where the viral replication takes place. The viral infection induces inflammation which leads to edema and necrosis of the bronchioles epithelium. Cough reflex occurs due to exposure of the subepithelial tissue and nerve fibers. Vascular permeablity increases leading to edema and swelling. Histopathologically, bronchiolitis obliterans shows intraluminal polyps, inflammatory infiltration and macrophages. Constrictive bronchiolitis shows thickening of the airways and interluminal narrowing.
Causes
Bronchiolitis usually affects children under the age of 2, with a peak age of 3 - 6 months. It is a common, and sometimes severe illness. Respiratory syncytial virus (RSV) is the most common cause. Other viruses that can cause bronchiolitis include adenovirus, influenza and parainfluenza. It may be caused by bacterial organisms like legionella pneumophila and mycoplasma pneumonia. Other non infectious causes include smoking, collagen vascular disease and post bone marrow transplant.
Differentiating Broncholitis from Other Diseases
Bronchiolitis must be differentiated from other respiratory and cardiac diseases that are presented with similar clinical manifestations. Based on cough and dyspnea, bronchiolitis is differentiated from asthma, COPD, pneumonia, congestive heart failure, diffuse idiopathic neuroendocrine cell hyperplasia, tuberculosis, pertussis, foreign body aspiration, pulmonary embolism and Harmann-Rich syndrome.
Epidemiology and Demographics
Bronchiolitis is one of the most common acute respiratory diseases that infects the infants and children. It affects around 3000 per 100,000 in the United States. It occurs during fall, winter and early spring. It can affect any age but it affects more the infants specially under 2 years. Bronchilitis ration in men is more than women and it is more common among the native americans, alaskans and hispanics. Bronchilitis has low mortality rate despite the high number of the hospitalizations.
Risk Factors
Bronchiolitis has different range of risk factors and it can be differentiated based on the age. In adult, common risk factors in the development of bronchiolitis include exposure to cigarette smoke, living in crowded areas and immunocompromised patients. In infants, the risk factors include age < 6 months, lack of breast-feeding, prematurity, and young children infected with congenital heart diseases.[3][4]
Natural History, Complications, and Prognosis
The first 2-3 days the patient with bronchiolitis presents with mild upper respiratory symptoms. Shortness of breath, wheezing, persistent prominent cough, tachypnea, chest wall retraction and nasal flaring usually develop between the third and seventh day. Symptoms gradually disappear within the next 2 weeks. Complications are usually observed among patients younger than 2 months of age, premature infants, and patients with other medical conditions (congenital heart disease, chronic pulmonary disease and immunodeficiencies). Severity scores can be used to estimate the prognosis.
Diagnosis
History and Symptoms
Bronchiolitis occurs mainly in the infants. The patients usually give history of nasal congestion and phlegm discharge. Its classical presentation is fever, cough and dyspnea. The virus is transmitted from person to person by direct contact with nasal fluids, or by airborne droplets. Although RSV generally causes only mild symptoms in an adult, it can cause severe illness in an infant. Bronchiolitis is seasonal and appears more often in the fall and winter months. It is a very common reason for infants to be hospitalized during winter and early spring. It is estimated that by their first year, more than half of all infants have been exposed to RSV.[5]
Physical Examination
Patients infected with bronchiolitis have toxic appearance and may be cyanotic. Fever is one of the signs of the disease but the lack of it does not exclude the diagnosis. Lung examination shows abnormalities in inspection and auscultation. In inspection, intercostal and substernal retractions can be observed. In auscultation, wheezing and crackles can be clearly heard with decrease in the respiratory sounds. Extrapulmonary manifestations can occur as well like pharyngitis, conjunctivitis, arrythmias, tachycardia and seizures.[6]
Laboratory Findings
Bronchiolitis diagnosis depends mainly on the symptoms and physical examination as the laboratory diagnosis is not specific for the disease. The lab tests include viral pathogen tests which are commonly used like ELISA, immunofluorescent assays and optical immunoassays. Complete blood count also is not specific for the bronchiolitis. Pulmonary function tests may be helpful in supporting the diagnosis and excluding other obstructive lung diseases.
X ray
Chest x-ray in cases of bronchiolitis is usually inspecific and may be inefficient for differentiating bronchiolitis from other lower respiratory tract infections. It may show atelectasis and consolidations. It is used also in excluding other medical conditions like pneumonia.
CT
CT scan shows non specific findigs in the cases of bronchiolitis that can be found in other diseases. These findings are like centrilobular nodules, bronchiolar wall thickening, ground glass appearance and parenchymal cysts.
MRI
There is no MRI findings associated with bronchiolitis.
Other Imaging Findings
There are no additional imaging findings for bronchiolitis.
Other Diagnostic Studies
There are no additional diagnostic findings for bronchiolitis.
Treatment
Medical Therapy
Therapy for bronchiolitis is mainly supportive. Supportive therapy includes frequent small feeds and oxygen therapy. In severe cases infants may require intravenous fluids and feeding via a nasogastric tube. In extreme cases, mechanical ventilation or the use of continuous positive airway pressure (CPAP) might be necessary. Prophylaxis is indicated in infants with hemodynamically significant heart disease and preterm infants who require >21% oxygen for at least the first 28 days of life. The drug of choice for prophylaxis is Palivizumab.
Surgery
Surgical intervention is not recommended for the management of bronchiolitis.
Primary Prevention
Prevention will relay in maintain proper measures to prevent the viral dissemination during the RSV season (handwash and avoid contact with patients with symptomatic respiratory infections) and prevention of tobacco smoke exposure. In patients with high risk of developing severe infections, pasive immunization with Palivizumanb is recommended.
Secondary Prevention
There is no secondary preventive measures available for bronchiolitis.
References
- ↑ Baar HS, Galindo J (1966). "Bronchiolitis fibrosa obliterans". Thorax. 21 (3): 209–14. PMC 1019027. PMID 5914992.
- ↑ Ryu JH, Myers JL, Swensen SJ (2003). "Bronchiolar disorders". Am J Respir Crit Care Med. 168 (11): 1277–92. doi:10.1164/rccm.200301-053SO. PMID 14644923.
- ↑ CDC https://www.cdc.gov/rsv/about/transmission.html Accessed on June 1, 2017
- ↑ Meissner HC (2016). "Viral Bronchiolitis in Children". N Engl J Med. 374 (1): 62–72. doi:10.1056/NEJMra1413456. PMID 26735994.
- ↑ Florin TA, Plint AC, Zorc JJ (2017). "Viral bronchiolitis". Lancet. 389 (10065): 211–224. doi:10.1016/S0140-6736(16)30951-5. PMID 27549684.
- ↑ Eisenhut M (2006). "Extrapulmonary manifestations of severe respiratory syncytial virus infection--a systematic review". Crit Care. 10 (4): R107. doi:10.1186/cc4984. PMC 1751022. PMID 16859512.