Reid index in increased in –
**Core Concept**
The Reid index is a pathological parameter used to assess the severity of chronic bronchitis. It is defined as the ratio of the thickness of the submucosal mucus gland layer to the total thickness of the bronchial wall. An increased Reid index is indicative of chronic bronchitis.
**Why the Correct Answer is Right**
In chronic bronchitis, the submucosal mucus glands are hypertrophied, leading to an increase in the thickness of the mucus gland layer. This, in turn, results in an elevated Reid index. The pathophysiology of chronic bronchitis involves chronic inflammation of the bronchial mucosa, which is triggered by repeated exposure to irritants such as cigarette smoke. The increased thickness of the mucus gland layer is a hallmark of chronic bronchitis and is used as a diagnostic criterion.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because the Reid index is not increased in acute bronchitis, where the inflammation is limited to the mucosa and submucosa, and the mucus gland layer is not significantly affected.
**Option B:** Incorrect because the Reid index is not a parameter used in the diagnosis of asthma, which is characterized by airway hyperresponsiveness and inflammation.
**Option C:** Incorrect because the Reid index is not increased in cystic fibrosis, which is a genetic disorder characterized by abnormal mucus production and thickening.
**Clinical Pearl / High-Yield Fact**
The Reid index is a useful parameter in the differential diagnosis of chronic respiratory diseases. A Reid index of 0.5 or greater is considered abnormal and is indicative of chronic bronchitis.
**Correct Answer: D.**