**Question:** Perifascicular atrophy of muscle fibres is seen in -

A. Facioscapulohumeral muscular dystrophy (FSHD)
B. Duchenne muscular dystrophy (DMD)
C. Emery-Dreifuss muscular dystrophy (EDMD)
D. Becker muscular dystrophy (BMD)

**Core Concept:** Perifascicular atrophy refers to the specific pattern of muscle fiber degeneration and regeneration that occurs in certain neuromuscular disorders. In this case, perifascicular atrophy is being tested for, which is a characteristic feature of certain muscular dystrophies.

**Why the Correct Answer is Right:** Perifascicular atrophy is seen in the following muscular dystrophies:

1. Facioscapulohumeral muscular dystrophy (FSHD) - This is a genetic disorder characterized by the selective degeneration of muscle fibers around the epimysium, the outermost layer of the muscle fascia. The fibers are preserved within the epimysium, leading to the distinctive "zebra" striped pattern on muscle biopsy.
2. Becker muscular dystrophy (BMD) - This is another genetic disorder characterized by milder clinical presentation and later onset compared to Duchenne muscular dystrophy (DMD). BMD presents with a more variable pattern of muscle fiber involvement, without the distinct perifascicular atrophy seen in FSHD.
3. Duchenne muscular dystrophy (DMD) - This is a severe X-linked genetic disorder characterized by generalized muscle weakness. Perifascicular atrophy is not typically seen in DMD due to the broader pattern of muscle fiber involvement and the absence of selective muscle fiber degeneration around the epimysium.
4. Emery-Dreifuss muscular dystrophy (EDMD) - This is a group of autosomal dominant or recessive genetic disorders characterized by generalized muscle weakness and joint contractures. Perifascicular atrophy is not seen in EDMD due to the different pattern of muscle fiber involvement and the absence of selective muscle fiber degeneration around the epimysium.

**Why Each Wrong Option is Incorrect:**

1. Facioscapulohumeral muscular dystrophy (FSHD) - This is a distinct entity from Duchenne and Becker muscular dystrophy. While FSHD involves the same muscle groups as Duchenne, the distinct perifascicular atrophy pattern is a key feature that sets FSHD apart from DMD.
2. Emery-Dreifuss muscular dystrophy (EDMD) - EDMD is a different entity from Duchenne and Becker muscular dystrophy. Perifascicular atrophy is not a feature of EDMD due to the distinct pattern of muscle fiber involvement and the absence of selective muscle fiber degeneration around the epimysium.
3. Facioscapulohumeral muscular dystrophy (FSHD) - DMD and BMD are characterized by generalized muscle weakness and the absence of perifascicular atrophy.