A 65-year-old man presents to his GP with vision loss, headaches and cold intolerance. He also mentions he has unintentionally gained 5kg in the last 3 months. On examination, he is found to have a bitemporal hemianopia and a pulse of 50 bpm. A thyroid function test is ordered. Which of the following test results is most likely to belong to this patient?

**Core Concept**
The patient's symptoms suggest a condition affecting the pituitary gland, given the combination of vision loss, headaches, and endocrine abnormalities such as cold intolerance and weight gain. **Hypopituitarism** or a **pituitary tumor** could be the underlying cause, affecting the production of various hormones, including thyroid-stimulating hormone (TSH).

**Why the Correct Answer is Right**
Given the patient's symptoms, such as bitemporal hemianopia indicating a possible pituitary tumor pressing on the optic chiasm, and signs of hypothyroidism (cold intolerance, weight gain), the most likely diagnosis is a condition leading to decreased TSH production, hence decreased thyroid hormone production. This scenario is consistent with secondary hypothyroidism, where the problem lies not with the thyroid gland itself but with the pituitary gland's inability to stimulate it.

**Why Each Wrong Option is Incorrect**
**Option A:** Would be indicative of primary hypothyroidism, where the issue lies within the thyroid gland itself, leading to elevated TSH levels as the pituitary tries to stimulate the thyroid.
**Option B:** Suggests hyperthyroidism, which does not align with the patient's symptoms of hypothyroidism.
**Option D:** Might represent a different endocrine issue but does not fit the clinical picture of hypopituitarism leading to secondary hypothyroidism.

**Clinical Pearl / High-Yield Fact**
In patients presenting with symptoms suggestive of hypothyroidism along with other endocrine deficiencies or visual field defects, consider **hypopituitarism** due to a pituitary tumor. This condition can lead to secondary hypothyroidism, characterized by low TSH and low free thyroxine (FT4) levels.

**Correct Answer:** D. Low TSH and low FT4.

✓ Correct Answer: A. TSH: Low T4: Low T3: Low