**Core Concept**
'Shrinking lung' is a term used to describe a decrease in lung volume, often due to inflammation and fibrosis in the lung parenchyma or pleura. This phenomenon is characterized by a reduced lung capacity, which can lead to respiratory symptoms such as dyspnea.

**Why the Correct Answer is Right**
Systemic Lupus Erythematosus (SLE) is a chronic autoimmune disease that can affect multiple organs, including the lungs. In SLE, the inflammation and fibrosis in the lung parenchyma can lead to a decrease in lung volume, resulting in the characteristic 'shrinking lung' phenomenon. This is often seen in patients with SLE who have a history of pleurisy or pleural effusions. The inflammation and fibrosis can lead to scarring and adhesions in the pleura, which can further reduce lung volume.

**Option A:**
Rheumatoid Arthritis (RA) is an autoimmune disease that primarily affects the joints, but it can also affect other organs such as the lungs. However, 'shrinking lung' is not a characteristic feature of RA. Instead, RA can lead to interstitial lung disease (ILD), which can cause inflammation and fibrosis in the lung parenchyma.

**Option C:**
Systemic Sclerosis (SSc) is an autoimmune disease that affects the skin and other organs, including the lungs. SSc can lead to ILD, which can cause inflammation and fibrosis in the lung parenchyma. However, 'shrinking lung' is not a specific feature of SSc.

**Option D:**
Polymyositis is an autoimmune disease that primarily affects the muscles, but it can also affect other organs such as the lungs. However, 'shrinking lung' is not a characteristic feature of polymyositis.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that 'shrinking lung' is a non-specific term that can be seen in various conditions, including SLE, RA, SSc, and others. A thorough clinical evaluation and diagnostic workup, including imaging studies and lung function tests, are necessary to determine the underlying cause of the 'shrinking lung' phenomenon.

**✓ Correct Answer: B. SLE. SLE is a chronic autoimmune disease that can affect multiple organs, including the lungs, and is characterized by inflammation and fibrosis in the lung parenchyma or pleura.**