**Core Concept:**
Acquired hypothyroidism is a condition characterized by a deficiency of thyroid hormones due to factors other than genetic causes, including autoimmune diseases and iatrogenic causes (e.g., medications, surgery, radiation). It is essential to understand the correct features to differentiate it from congenital hypothyroidism.

**Why the Correct Answer is Right:**
The correct answer is "Option D: Hashimoto's thyroiditis" because Hashimoto's thyroiditis is a common cause of primary hypothyroidism due to an autoimmune disorder, where the body's immune system attacks the thyroid gland, leading to decreased hormone production.

**Why Each Wrong Option is Incorrect:**

**Option A: Cushing's syndrome** refers to a condition characterized by symptoms and signs due to prolonged exposure to high cortisol levels. The common cause of Cushing's syndrome does not involve thyroid dysfunction, making it irrelevant to acquired hypothyroidism.

**Option B: Addison's disease** is another autoimmune disorder characterized by decreased cortisol production due to immune-mediated destruction of the adrenal glands. While both Cushing's syndrome and Addison's disease involve autoimmune disorders, they do not directly relate to acquired hypothyroidism.

**Option C: DKA (Diabetic Ketoacidosis)** is a life-threatening complication of diabetes mellitus characterized by hyperglycemia, ketonemia, and ketonuria. DKA is unrelated to thyroid function and does not contribute to acquired hypothyroidism.

**Correct Answer:** .