**Question:** Target fibres are characteristically seen in a muscle biopsy of-

A. Post-inflammatory fibres
B. Duchenne muscular dystrophy
C. Myopathic fibres
D. Hypoxic fibres

**Correct Answer:** C. Myopathic fibres

**Core Concept:** Target fibres are a characteristic feature of muscle biopsy in various myopathic conditions, which refers to diseases affecting muscle function and structure. These fibres are centrally nucleated, meaning that their nucleus is located at the center of the fibre, rather than at the periphery as in normal adult skeletal muscles.

**Why the Correct Answer is Right:** In myopathic conditions, the muscle fibres undergo atrophy, regeneration, and subsequent hypertrophy, leading to the formation of centrally nucleated fibres. These fibres are also known as "target" fibres due to the appearance of a dark central nucleus surrounded by a pale rim, often referred to as the "target" pattern.

**Why Each Wrong Option is Incorrect:**

A. Post-inflammatory fibres: These fibres are typically characterized by inflammation and are not centrally nucleated. Post-inflammatory fibres are usually found in muscle biopsies following a recent muscle injury or inflammation, making it an incorrect option for target fibres.

B. Duchenne muscular dystrophy (DMD): DMD is a genetic disorder affecting muscle proteins, primarily affecting boys under the age of 6 years. While muscle biopsy may reveal some features of dystrophin deficiency, it would not specifically demonstrate target fibres, making this option incorrect.

D. Hypoxic fibres: Hypoxic fibres are fibres that have been exposed to low oxygen levels and are characterized by features like vacuolation, ragged red fibers, and COX negative fibers. These are not centrally nucleated and hence are not target fibres.

**Clinical Pearl:**

Target fibres are an important feature to recognize in muscle biopsy for diagnosing myopathic conditions. A comprehensive evaluation of muscle biopsy findings, including fibre size, shape, and the presence of other specific features, is essential for accurate diagnosis and appropriate management of patients.

In conclusion, recognizing target fibres in a muscle biopsy can help in diagnosing myopathic conditions like limb girdle muscular dystrophy, limb-girdle congenital muscular dystrophy, and certain forms of mitochondrial myopathy. These conditions often present with a combination of muscle weakness, hypotonia, and reduced muscle mass. Early diagnosis and treatment initiation can significantly improve the prognosis and quality of life for the patient.