A boy presented with weakness in lower limbs, calf hyperophy, positive Gower’s sign and an elevated CPK value of 10,000. The most likely diagnosis is:
**Core Concept**
The question is testing the student's knowledge of a specific neuromuscular disorder characterized by progressive muscle weakness, muscle hypertrophy, and elevated creatine phosphokinase (CPK) levels. This condition is caused by a genetic mutation affecting the dystrophin protein, leading to muscle fiber degeneration and replacement by connective tissue.
**Why the Correct Answer is Right**
The correct answer is Duchenne Muscular Dystrophy (DMD), a severe form of muscular dystrophy that affects boys due to an X-linked recessive gene mutation. The elevated CPK value of 10,000 indicates significant muscle damage. Gower's sign, a characteristic finding in DMD, is the inability to stand up from the floor without using the hands to push off. Calf hypertrophy is a common feature of DMD, resulting from the replacement of muscle tissue with connective tissue. The dystrophin protein plays a crucial role in maintaining muscle cell integrity, and its deficiency leads to progressive muscle weakness and degeneration.
**Why Each Wrong Option is Incorrect**
* **Option A:** Becker Muscular Dystrophy is a milder form of muscular dystrophy, typically presenting later in life, and is characterized by a slower progression of symptoms. It is not associated with calf hypertrophy or a positive Gower's sign.
* **Option B:** Facioscapulohumeral Muscular Dystrophy is a distinct form of muscular dystrophy that primarily affects the muscles of the face, scapula, and humerus. It does not typically present with calf hypertrophy or elevated CPK levels.
* **Option C:** Myotonic Dystrophy is a different form of muscular dystrophy characterized by myotonia (a delay in muscle relaxation after contraction) and wasting of the muscles. It is not typically associated with calf hypertrophy or a positive Gower's sign.
**Clinical Pearl / High-Yield Fact**
Becker Muscular Dystrophy and Duchenne Muscular Dystrophy are both caused by mutations in the dystrophin gene, but the former is generally milder and has a later onset. A high CPK value, calf hypertrophy, and a positive Gower's sign are key clinical features distinguishing DMD from other forms of muscular dystrophy.
**Correct Answer:** C.