Carpet tack sign seen in –
**Core Concept**
The carpet tack sign is a radiological finding associated with a specific condition. It is characterized by a pattern of calcification seen on imaging studies. This sign is indicative of a particular disease process affecting the lungs.
**Why the Correct Answer is Right**
The carpet tack sign is seen in pulmonary alveolar microlithiasis (PAM), a rare disease characterized by the formation of small calcium deposits within the alveoli of the lungs. These deposits appear as small, scattered calcifications on chest radiographs, resembling the pattern of carpet tacks. The exact cause of PAM is unknown, but it is thought to be related to abnormal calcium metabolism.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the carpet tack sign is specifically associated with PAM, not with other conditions such as pneumoconiosis or pulmonary tuberculosis.
**Option B:** This option is incorrect because the carpet tack sign is not a characteristic finding in metastatic calcification, which typically presents with larger, more diffuse calcifications.
**Option C:** This option is incorrect because the carpet tack sign is not a feature of chronic obstructive pulmonary disease (COPD), which is characterized by airway narrowing and emphysema.
**Clinical Pearl / High-Yield Fact**
The carpet tack sign is a classic radiological finding in PAM, and its presence should prompt further investigation to confirm the diagnosis. PAM is a rare but important condition to recognize, as it can have implications for lung transplantation and other treatments.
**Correct Answer: D. Pulmonary alveolar microlithiasis (PAM).**