Thyrotoxic myopathy affects ?
**Core Concept**
Thyrotoxic myopathy is a condition associated with **hyperthyroidism**, characterized by muscle weakness and wasting due to the excess of **thyroid hormones**. This condition affects the skeletal muscles, leading to proximal muscle weakness. The underlying mechanism involves the catabolic effects of excess **thyroid hormones** on muscle tissue.
**Why the Correct Answer is Right**
The correct answer is related to the fact that thyrotoxic myopathy primarily affects the proximal muscles, which are responsible for movements such as shoulder and hip movements. The excess **thyroid hormones** lead to an increase in the breakdown of muscle proteins, resulting in muscle weakness and wasting. This condition is often reversible with treatment of the underlying **hyperthyroidism**.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because thyrotoxic myopathy does not typically affect the cardiac muscle directly, although **hyperthyroidism** can lead to cardiac complications.
**Option B:** This option is incorrect as thyrotoxic myopathy is not primarily associated with smooth muscle.
**Option C:** This option might seem plausible but is incorrect because, while **hyperthyroidism** can have widespread effects, thyrotoxic myopathy specifically refers to its impact on skeletal muscle.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that thyrotoxic myopathy is a reversible condition with appropriate treatment of **hyperthyroidism**, emphasizing the importance of early diagnosis and management. Muscle weakness, particularly in the proximal muscles, should prompt consideration of thyroid function tests.
**Correct Answer:** D. Skeletal muscle.