A 7 year old child presents with non productive cough, mild stridor since 6 months. On oral antibiotics, patient is improving but suddenly develops wheezing, productive cough, mild fever. X–ray shows hyperlucency and PFT shows obstructive curve. Most probable diagnosis is –
Bronchiolitis obliterans

Bronchiolitis obliterans. is a rare chronic lung disease of the bronchioles and smaller airways
Bronchiolitis obliterans most commonly occurs in pediatric population after respiratory infections (i.e. adenovirus, mycoplasma, measles, influenza, pertussis).
Other causes include connective tissue disease (i.e. juvenile rheumatoid arthritis, systemic lupus erythematosis, scleroderma)
Bronchiolitis occurs in all age groups.


Pathogenesis

After the initial insult, inflammation affecting terminal bronchioles, respiratory bronchioles and alveolar ducts may result in obliteration of the airway lumen.
Epithelial damage resulting in abnormal repair is characteristic of bronchiolitis obliterans.
Complete or partial obstruction of the airway lumen may result in air trapping or atelactasis.

Clinical manifestations

Cough, fever, cyanosis and respiratory distress followed by initial improvement may be the initial signs of bronchiolitis obliterans.
Progression of the disease may ensue with increasing dyspnoea, cough, sputum production and wheezing.
Chest radiographs may be relatively normal compared with the extent of physical findings but may demonstrate hyperluscency and patchy infiltrates (occasionally, a swyer James syndrome, i.e. a unilateral hyperluscent lung has developed).
Pulmonary function tests demonstrate varaible findings but typically shows signs of airway obstruction.
Ventilation perfusion scan shows a typical motheaten appearance of multiple matched defects in ventilation and perfusion.
CT scan demonstrates patchy areas of hyperluscency.
Open lung biopsy or transbronchial biopsy remains the best means of establishing the diagnosis of bronchiolitis obliterans.

Treatment

No definite therapy exists for bionchiolitis obliterans.
Administration of corticosteroids may be beneficial

About other options
Follicular bronchitis

It is a lyinphoproliferative lung disorder characterized the presence of lymphoid follicles, coursing along the airways (bronchi or bronchioles)
It is rare in children.
Although the cause is unknown, an infectious aetiology has been proposed.
Onset of symptoms generally occurs by 6 weeks of age and peaks between 6 and 18 months.
Cough, moderate fever and fine crackles are common clinical findings.
Fine crackles generally, persist over time and recurrence of symptoms is common.
Chest radiographs may be relatively benign initially but evolve into the typical interstitial pattern.
Pulmonary function tests show restrictive pattern
Chest CT shows fine reticular pattern.
Open lung biopsy is used to make definitive diagnosis.


Pulmonary alveolar microlithiasis


This is a rare disorder.
Although the underlying cause of pulmonary alveolar microlithiasis is unknown, the disease is characterized by the formation of lamellar concretions of calcium phosphate or "inicrolith", within the alveoli, creating a classic pattern on the radiograph.
Chest radiography typically reveal bilateral infiltrates with a fine sandlike micronodular appearance.
Although the mean age at the time of diagnosis is in the mid 30s the onset of the disease can occur during childhood.
When symptomatic, individuals with pulmonary alveolar microlithiasis usually complain of dyspnoea on exertion and non productive cough.
Physical examinations of the lungs may reveal fine inspiratory crackles and diminished breath sounds. Clubbing occurs, although this is usually a more advanced sign.
Children are often asymptomatic on initial presentation.
Diagnosis
Chest radiography typically reveals b/L infiltrate with a fine sandlike micronodular appearance or "Sandstorm" appearance.
CT scan shows diffuse micronodular calcified densities.
Open lung biopsy reveals laminated calcific ioncretions within the alceoli.
Post viral syndrome
Bronchiolitis obliterans
Follicular bronchitis
Pulmonary alveolar microlithiasis