**Core Concept**
The follow-up of a patient who has undergone total thyroidectomy for papillary carcinoma of the thyroid involves monitoring for recurrence or metastasis. This is crucial due to the potential for lymph node metastasis and distant spread of the disease. The marker used for follow-up in such cases is a tumor-specific antigen that is often elevated in the serum of patients with thyroid cancer.

**Why the Correct Answer is Right**
Calcitonin is a hormone produced by the parafollicular cells (also known as C-cells) of the thyroid gland. In patients with medullary thyroid carcinoma (MTC), calcitonin levels are often elevated. However, in the context of papillary thyroid carcinoma (PTC), the relevant tumor marker is thyroglobulin (Tg). Thyroglobulin is a protein produced by the follicular cells of the thyroid gland, and its levels are often elevated in patients with PTC. During follow-up, thyroglobulin levels are measured to detect recurrence or metastasis.

**Why Each Wrong Option is Incorrect**
**Option A:** Calcitonin - This is incorrect because calcitonin is primarily associated with medullary thyroid carcinoma (MTC), not papillary thyroid carcinoma (PTC).

**Option B:** TSH - This is incorrect because while TSH (thyroid-stimulating hormone) is used to stimulate the thyroid gland during follow-up, it is not a tumor marker itself.

**Option C:** CA-125 - This is incorrect because CA-125 is a tumor marker associated with ovarian cancer, not thyroid cancer.

**Option D:** CEA - This is incorrect because CEA (carcinoembryonic antigen) is a tumor marker associated with various types of cancer, including colorectal and lung cancer, but it is not specific for thyroid cancer.

**Clinical Pearl / High-Yield Fact**
Thyroglobulin (Tg) levels should be measured in patients with papillary thyroid carcinoma (PTC) during follow-up to detect recurrence or metastasis. A rising Tg level may indicate disease recurrence, even in the absence of detectable iodine uptake on radioactive iodine scans.

**Correct Answer: B. TSH**