**Core Concept:** Pseudohypertrophy is a condition characterized by apparent muscle enlargement due to increased extracellular fluid volume, while muscle mass remains normal or even reduced. It is a clinical presentation seen in certain neuromuscular disorders and drug-induced conditions affecting neuromuscular transmission.

**Why the Correct Answer is Right:**

The correct answer is **D.** Facioscapulohumeral muscular dystrophy (FSHD), a type of muscular dystrophy, is often inherited and can present with pseudohypertrophy of the calf muscles due to muscle weakness and atrophy. In FSHD, there is a decrease in the expression of the DUX4 gene, leading to reduced dystrophin production and subsequent muscle damage. The pseudohypertrophy is a result of increased extracellular fluid volume and decreased muscle mass.

**Why Each Wrong Option is Incorrect:**

A. **Maternal uncle having the same illness (Congenital Muscular Dystrophy)**: While familial history is a significant clue, the clinical presentation of pseudohypertrophy in this case does not match the typical symptoms of congenital muscular dystrophies.

B. **Muscle biopsy showing myopathic changes**: A muscle biopsy can reveal myopathic changes in various conditions, but the correct diagnosis is based on the clinical presentation, family history, and other diagnostic tests like electromyography and genetic testing.

C. **Klinefelter syndrome**: Although this condition can present with muscular symptoms, pseudohypertrophy is not a common feature.

**Clinical Pearl:**

In cases of pseudohypertrophy, it is essential to combine clinical presentation, family history, and additional diagnostic tests to arrive at an accurate diagnosis. A proper workup including electromyography, genetic testing, and referral to a specialist could lead to the correct diagnosis and appropriate management of the patient.