A female of 40 years presenting with intolerance to cold, constipation and hoarseness of voice was found to have cardiomegaly on chest roentgenogram. Which of the following investigations is the best to determine the cause of her cardiomegaly?
**Core Concept**
The patient's presentation suggests an underlying condition that affects the thyroid gland, leading to a hormonal imbalance. The symptoms of intolerance to cold, constipation, and hoarseness of voice are classic for hypothyroidism, a condition characterized by decreased production of thyroid hormones. Cardiomegaly (enlargement of the heart) is a common finding in hypothyroidism due to the deposition of mucopolysaccharides in the heart tissue, leading to increased cardiac muscle mass.
**Why the Correct Answer is Right**
The best investigation to determine the cause of cardiomegaly in this patient would be a Thyroid Function Test (TFT), specifically a measurement of Thyroid-Stimulating Hormone (TSH). TSH is a hormone produced by the pituitary gland that regulates the production of thyroid hormones (T3 and T4) by the thyroid gland. An elevated TSH level indicates primary hypothyroidism, where the thyroid gland is not producing enough thyroid hormones. A TFT will help confirm the diagnosis of hypothyroidism and guide treatment.
**Why Each Wrong Option is Incorrect**
* **Option A:** Echocardiogram is a useful investigation for assessing cardiac structure and function, but it does not provide information on the underlying cause of cardiomegaly.
* **Option B:** Chest X-ray is a basic investigation that may show cardiomegaly, but it does not provide any information on the underlying cause.
* **Option D:** Electrocardiogram (ECG) is a useful investigation for assessing cardiac rhythm and conduction, but it does not provide any information on the underlying cause of cardiomegaly.
**Clinical Pearl / High-Yield Fact**
In patients with suspected hypothyroidism, a low TSH level can indicate secondary hypothyroidism, where the pituitary gland is not producing enough TSH. This is often due to a pituitary tumor or other pituitary pathology.
**Correct Answer:** D. Electrocardiogram (ECG)