**Core Concept**
Myxoedema is a clinical condition characterized by hypothyroidism, particularly in its severe and chronic form. It is associated with a range of systemic symptoms and physical findings due to the decreased metabolic rate and impaired thyroid hormone production.

**Why the Correct Answer is Right**
Myxoedema is caused by a deficiency of thyroid hormones, which are essential for regulating metabolism, growth, and development. In myxoedema, the decreased production of thyroid hormones leads to a range of systemic effects, including weight gain, fatigue, cold intolerance, and dry skin. The condition is often associated with a decrease in the level of thyroxine (T4) and triiodothyronine (T3) hormones in the blood.

**Why Each Wrong Option is Incorrect**
**Option A:**
This option is incorrect because myxoedema is indeed characterized by a decreased production of thyroid hormones, which is a direct result of hypothyroidism.

**Option B:**
This option is incorrect because myxoedema is not caused by an excess of thyroid hormones, but rather a deficiency.

**Option C:**
This option is incorrect because myxoedema is not typically associated with an increase in the level of thyroxine (T4) and triiodothyronine (T3) hormones in the blood.

**Clinical Pearl / High-Yield Fact**
A key clinical feature of myxoedema is the presence of a characteristic skin fold, known as a "triple fold" sign, which is a thickened fold of skin that forms when the skin is pinched between the thumb and index finger. This sign is a classic indicator of myxoedema and should be remembered by exam candidates.

**Correct Answer:** A, B, C