## **Core Concept**
Facioscapulohumeral muscular dystrophy (FSHD) is a type of muscular dystrophy characterized by weakness of specific muscle groups, particularly those of the face (facio-), scapula (scapulo-), and upper arm (humeral). The condition results from a genetic defect leading to progressive muscle weakness and wasting.

## **Why the Correct Answer is Right**
The correct answer, , refers to muscles that are relatively spared in FSHD. In FSHD, muscles around the scapula, face, and upper arm are typically involved early and significantly. However, certain muscle groups are relatively spared, including the **distal muscles of the lower limbs** and some proximal muscles. The relative sparing of certain muscle groups is a hallmark of FSHD, distinguishing it from other muscular dystrophies.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Incorrect because muscles in this region are often involved in FSHD, particularly those around the scapula and face.
- **Option B:** Incorrect as FSHD characteristically affects muscles in this area, leading to notable weakness and atrophy.
- **Option C:** Incorrect because while some muscles may show variability in weakness, FSHD predominantly affects muscles in the facial, scapular, and humeral regions.

## **Clinical Pearl / High-Yield Fact**
A key clinical feature of FSHD is the **asymmetric** and **variable** progression of muscle weakness. A classic sign is the difficulty in raising the arms above the head due to scapular winging, which results from weakness of the scapular stabilizers. Early involvement of the facial muscles leading to a characteristic facial appearance (e.g., inability to close the eyes tightly) is another hallmark.

## **Correct Answer:** D.