**Question:** Drugs of choice in diffuse pan bronchiolitis is

A. Salbutamol
B. Ipratropium
C. Oral corticosteroids
D. Nitric oxide inhalation

**Core Concept:** Diffuse panbronchiolitis (DPB) is a chronic obstructive pulmonary disease characterized by inflammation and destruction of the small airways leading to airflow limitation. DPB is seen predominantly in smokers and is often associated with HLA-B27 positivity.

**Why the Correct Answer is Right:** B. Ipratropium is a muscarinic antagonist that inhibits the action of acetylcholine on muscarinic receptors in the bronchial smooth muscles, leading to relaxation of the smooth muscles and bronchodilation. This is particularly relevant in DPB, where increased bronchoconstriction and airway hyperresponsiveness contribute to the disease progression.

**Why Each Wrong Option is Incorrect:**

A. Salbutamol (beta-2 agonist) is effective in acute exacerbations of DPB, but it does not have a long-term benefit and does not address the underlying inflammation and airway obstruction.

C. Oral corticosteroids may provide symptomatic relief but do not reverse the disease progression, and long-term use may lead to adverse effects.

D. Nitric oxide inhalation is primarily used in pulmonary arterial hypertension and does not address the airway inflammation and obstruction characteristic of DPB.

**Clinical Pearl:** In DPB, the choice of treatment should focus on addressing the airway inflammation and hyperresponsiveness. The use of ipratropium provides bronchodilation and helps in improving symptoms and lung function in DPB patients. Salbutamol is useful in acute exacerbations but does not address the chronic airway inflammation and obstruction. Corticosteroids and nitric oxide inhalation are not specific treatments for DPB and may have limited efficacy or adverse effects.