**Core Concept**
Medullary thyroid carcinoma (MTC) is a rare type of thyroid cancer that originates from the parafollicular cells, also known as C-cells, which produce calcitonin. This cancer is characterized by its unique histological features and clinical manifestations.

**Why the Correct Answer is Right**
Medullary carcinoma of the thyroid indeed arises from the parafollicular cells, which are responsible for the production of calcitonin. The presence of amyloid stroma in the tumor is a hallmark feature of MTC, resulting from the deposition of amyloid protein produced by the tumor cells. Approximately 25% of MTC cases are familial, often associated with multiple endocrine neoplasia type 2 (MEN2) syndromes. Diarrhea can occur in patients with MTC due to the excessive production of calcitonin, which can lead to gastrointestinal symptoms. Total thyroidectomy is the recommended surgical treatment for MTC, as it is the only curative option.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not provide a comprehensive answer. MTC is indeed associated with parafollicular cells, but this option does not address the other features of the disease.

**Option B:** This option is incorrect as it implies that the presence of amyloid stroma is not a characteristic feature of MTC. While amyloid stroma is a hallmark of MTC, it is not the only feature of the disease.

**Option C:** This option is incorrect as it states that only 10% of cases are familial, which is an underestimate. Approximately 25% of MTC cases are familial.

**Option D:** This option is incorrect as it implies that diarrhea is not a symptom of MTC. Diarrhea can occur in patients with MTC due to the excessive production of calcitonin.

**Clinical Pearl / High-Yield Fact**
MTC is a unique type of thyroid cancer that requires a high index of suspicion, especially in patients with a family history of the disease. The presence of amyloid stroma and elevated calcitonin levels are key diagnostic features of MTC.

**Correct Answer: D. 5. Total thyroidectomy is performed**