It is a serious illness, characterized by inflammation of bronchioles, causing severe dyspnea. Infants are the most likely candidates.
Etiopathogenesis
The exact etiology is not clear. An overwhelming majority has a viral etiology. RSV* leads the list followed by influenza viruses, adenovirus, herpes virus, parainfluenza virus; rarely, primary atypical pneumonia organisms (Mycoplasma pneumonia species) may be responsible for bronchiolitis.
Certain bacteria (Haemophilus influenzae, Pneumococcus, Streptococcus hemolyticus) and allergy have also been incriminated. However, there is no convincing evidence in support of this. As a result of inflammation, exudate, edema, and contraction of the circular musculature of the bronchioles, there occurs a sort of partial obstruction in the lumen of the bronchioles followed by trapping of the air within the alveoli, resulting in areas of emphysema during expiration. The trapped air gets absorbed when obstruction becomes complete, causing areas of collapse (atelectasis). Finally, hypoxemia (from poor ventilation and diffusion) and respiratory acidosis (from CO2 retention) may occur.
Epidemiology
Bronchiolitis is more or less confined to winter and early spring and occurs globally. It is primarily a disease of the first 2 years of life, the peak incidence occurring around 6 months of age. Even neonates (especially preterm) may suffer from bronchiolitis. Both epidemic and sporadic forms occur.
Clinical Features
Most cases of bronchiolitis have a mild illness and may not even report to a medical facility. Manifestations are mild and settle within a few days without any medical intervention.
- Following a mild upper respiratory tract infection, bronchiolitis abruptly manifests with dyspnea (rapid shallow breathing) and prostration.
- Cough is either absent or simply mild.
- Mild-to-moderate fever is usually present.
- If dyspnea is marked, air hunger, flaring of alae nasi, chest retractions, and cyanosis may be there.
- Dehydration and respiratory acidosis may complicate the clinical features.
- Chest signs include intercostal, subcostal, and suprasternal retractions, hyper-resonant percussion note (this is because of emphysema which may also push the liver and spleen down), diminished breath sounds and widespread crepitations, and wheezing.
Differential Diagnosis
Bronchiolitis requires to be differentiated from:
- Asthma (known for frequent exacerbations)
- Bacterial pneumonia (wheezing either absent or only mild)
- Foreign body in trachea [history of foreign body (FB), localized wheeze, signs of collapse/emphysema].
