## **Core Concept**
Sarcoidosis is a **multisystem granulomatous disease** characterized by the formation of non-caseating granulomas in various organs. The etiology of sarcoidosis remains unknown, but it is believed to result from a combination of genetic and environmental factors. The disease can affect any organ, but some organs are more commonly involved than others.

## **Why the Correct Answer is Right**
The lungs are the most common organ involved in sarcoidosis, with **pulmonary involvement occurring in approximately 90% of cases**. The disease often presents with **bilateral hilar lymphadenopathy (BHL)** and may progress to pulmonary fibrosis. The lungs are primarily affected due to the inhalation of antigens, which is thought to trigger the granulomatous response in susceptible individuals.

## **Why Each Wrong Option is Incorrect**
* **Option A:** While the skin can be involved in sarcoidosis, manifesting as erythema nodosum, plaques, or papules, it is not the most common organ involved.
* **Option B:** The eyes can also be affected, with uveitis being a common manifestation, but they are not the most frequently involved organs.
* **Option C:** The liver is often involved, with granulomas found in liver biopsies, but it is not the most common organ involved, and liver dysfunction is rarely a presenting feature.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that **sarcoidosis can affect any organ, but the lungs and lymph nodes are most commonly involved**. A classic presentation is **Löfgren's syndrome**, which includes bilateral hilar lymphadenopathy, erythema nodosum, and joint symptoms. This syndrome often has a good prognosis.

## **Correct Answer:** .