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What is the most common cause of hyperthyroidism?
- A. Thyroiditis
- B. Toxic thyroid adenoma
- C. Toxic multinodular goitre
- D. Grave's disease
Correct Answer: D
Rationale: Grave's disease is the most common cause of hyperthyroidism. It is an autoimmune disorder where the body's immune system mistakenly attacks the thyroid gland, leading to overproduction of thyroid hormones. This results in symptoms such as weight loss, rapid heartbeat, heat intolerance, and tremors. While toxic thyroid adenoma, toxic multinodular goitre, and thyroiditis are also potential causes of hyperthyroidism, Grave's disease is the most prevalent among them.
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Which of the following is not a neuromuscular feature of thyrotoxicosis?
- A. Myasthenic syndrome
- B. Brisk knee jerk
- C. Hypokalaemic periodic paralysis
- D. Hyperkinesia
Correct Answer: A
Rationale: Thyrotoxicosis typically presents with hypermetabolism and various neuromuscular manifestations. Myasthenic syndrome, which involves muscle weakness and fatigability, is not a common neuromuscular feature of thyrotoxicosis. Instead, manifestations such as brisk knee jerk reflexes, hypokalaemic periodic paralysis (due to shifts in potassium levels), and hyperkinesia (excessive movement) are more commonly observed in patients with thyrotoxicosis. Myasthenic syndrome is more commonly associated with autoimmune disorders affecting the neuromuscular junction, such as myasthenia gravis.
All of the following represent examples of hypothalamic-pituitary negative feedback except:
- A. Cortisol on the CRH-ACTH axis
- B. Gonadal steroids on the GnRH-LH/FSH axis
- C. IGF-1 on the growth hormone-releasing hormone (GHRH)-GH axis
- D. Renin-angiotensin-aldosterone axis
Correct Answer: D
Rationale: The renin-angiotensin-aldosterone axis does not involve the hypothalamus or pituitary gland; instead, it primarily involves the kidneys and the renin-secreting cells. In this axis, renin is released in response to low blood pressure, leading to the formation of angiotensin II and the subsequent release of aldosterone from the adrenal glands. Feedback mechanisms for this axis primarily involve the regulation of renin release based on blood pressure rather than involving direct negative feedback from downstream hormones on the hypothalamus or pituitary gland. On the other hand, choices A, B, and C all involve classic examples of hypothalamic-pituitary negative feedback loops where the end hormone suppresses the release of the stimulating hormones at the hypothalamic and pituitary levels.
Oxytocin and antidiuretic hormone (ADH; vasopressin) are:
- A. complex steroids.
- B. synthesized and stored in the posterior pituitary.
- C. released from the anterior pituitary where blood is hypotonic.
- D. synthesized in the hypothalamus and released from the posterior pituitary.
Correct Answer: D
Rationale: Oxytocin and antidiuretic hormone (ADH; vasopressin) are both synthesized in the hypothalamus, specifically in the supraoptic and paraventricular nuclei. After synthesis, they are transported along axons to the posterior pituitary where they are stored until they are released into the bloodstream when needed. This is why they are released from the posterior pituitary, not the anterior pituitary. These hormones have different functions in the body, with oxytocin being involved in labor and breastfeeding, while ADH plays a role in regulating water balance and blood pressure.
Which of the following tests should be used to make the diagnosis of Cushing's syndrome?
- A. 24-hour urine free cortisol
- B. Corticotropin-releasing hormone (CRH) level at 8 a.m.
- C. Inferior petrosal venous sampling
- D. Overnight 1-mg dexamethasone suppression test
Correct Answer: D
Rationale: The overnight 1-mg dexamethasone suppression test is commonly used as an initial screening test for Cushing's syndrome. In this test, a patient takes 1 mg of dexamethasone orally at 11 p.m., and their serum cortisol level is measured the next morning. In patients with Cushing's syndrome, the cortisol levels will not be suppressed by the dexamethasone due to the presence of excessive cortisol production.
Commonest cause of 'ambiguous genitalia' in newborn is:
- A. Congenital adrenal hyperplasia
- B. True hermaphroditism
- C. Testicular ferminisation syndrome
- D. Pseudo-hermaphroditism
Correct Answer: A
Rationale: Congenital adrenal hyperplasia (CAH) is the most common cause of ambiguous genitalia in newborns. This condition is due to a deficiency of enzymes in the adrenal gland that are necessary for the production of cortisol. As a result, the body produces excess androgens (masculinizing hormones), leading to abnormal genital development in females. The external genitalia may appear ambiguous, with features of both male and female genitalia. This condition can be detected through newborn screening and confirmed through further hormonal and genetic testing. Treatment involves hormone replacement therapy to normalize hormone levels and surgery may be required to reconstruct the genitalia.