Which is the commonest site for extrapulmonary TB ?
**Core Concept**
Extrapulmonary tuberculosis (TB) is a form of TB that affects organs other than the lungs, such as the lymph nodes, bones, joints, and other tissues. Extrapulmonary TB accounts for approximately 10-15% of all TB cases worldwide.
**Why the Correct Answer is Right**
The commonest site for extrapulmonary TB is the lymph nodes, particularly the cervical lymph nodes. This is because the lymphatic system plays a crucial role in the spread of TB bacteria from the lungs to other parts of the body. The bacteria can enter the lymphatic vessels and travel to the nearest lymph nodes, where they can cause infection and inflammation. The cervical lymph nodes are a common site for extrapulmonary TB due to their proximity to the lungs and the throat.
**Why Each Wrong Option is Incorrect**
* **Option A:** While the pleura is a common site for pulmonary TB, it is not typically considered an extrapulmonary site.
* **Option B:** The spine is a common site for skeletal TB, but it is not the most common site for extrapulmonary TB.
* **Option D:** The skin is a rare site for extrapulmonary TB, and while it can occur, it is not the most common site.
**Clinical Pearl / High-Yield Fact**
In patients with suspected extrapulmonary TB, a thorough physical examination and imaging studies, such as CT scans or MRI, can help identify the affected site. A high index of suspicion and a thorough medical history are essential in diagnosing extrapulmonary TB.
**Correct Answer: C. The lymph nodes, particularly the cervical lymph nodes.**