**Question:** All of the following are true for sarcoidosis except: September 2008

A. Sarcoidosis is a granulomatous disease affecting multiple organs.
B. Sarcoidosis is a common disease in the United States.
C. Sarcoidosis is caused by Mycobacterium tuberculosis infection.
D. Sarcoidosis is a disease primarily affecting the lungs.

**Core Concept:** Sarcoidosis is a multisystem granulomatous disease characterized by the presence of non-caseating granulomas, primarily involving the lungs, lymph nodes, and skin. It is a systemic disorder that can affect various organs. The correct answer should emphasize the multisystem nature of the disease and its granulomatous feature.

**Why the Correct Answer is Right:** The correct answer, option D, highlights the pulmonary involvement in sarcoidosis while acknowledging its multisystem nature. Sarcoidosis is primarily characterized by granulomas in the lungs, lymph nodes, and skin, with systemic manifestations. Although the disease can affect multiple organs, the focus should be on its granulomatous feature, making "primarily affecting the lungs" the correct choice.

**Why Each Wrong Option is Incorrect:**

A. While sarcoidosis is indeed a granulomatous disease affecting multiple organs, the statement "Sarcoidosis is a granulomatous disease affecting multiple organs" is incorrect due to the inclusion of "Sarcoidosis is a granulomatous disease affecting multiple organs" in the correct answer.

B. Sarcoidosis is not a common disease in the United States, but this option is incorrect because it does not address the multisystem involvement in the disease.

C. Mycobacterium tuberculosis is the causative agent of tuberculosis, not sarcoidosis. Sarcoidosis is a distinct disease characterized by non-caseating granulomas, which is a crucial aspect of the disease that distinguishes it from tuberculosis.

**Clinical Pearl:** Sarcoidosis is a multisystem granulomatous disease with a prevalence ranging from 15 to 40 cases per 100,000 people per year (approximately 10-20 cases per 100,000 people per year). The disease is more common in African Americans, Scandinavians, and Japanese people. This information helps to understand the demographics of the disease and can be useful in clinical practice when making a differential diagnosis or considering the possibility of sarcoidosis in patients presenting with multisystem involvement.