DFT-MEDICINE D1-08/10/2025-MaXeMo

A middle-aged woman with progressively enlarging hands and feet is diagnosed with a pituitary adenoma. The over-secreted hormone mediates its effects on cellular growth primarily through which signaling protein?

• Janus Kinase (JAK)

• SMAD

• Gαs

• Retinoid X Receptor (RXR)

Answer explanation

The clinical picture is of acromegaly, caused by excess Growth Hormone (GH). The GH receptor is a cytokine receptor that lacks intrinsic kinase activity and signals via the associated Janus Kinase (JAK)-STAT pathway.

A 48-year-old male is on the neurosurgery ward, day 8 post-transsphenoidal resection of a large pituitary macroadenoma. He develops confusion and a severe headache. His labs reveal a serum sodium of 122 mEq/L, serum osmolality of 260 mOsm/kg, and a urine osmolality of 450 mOsm/kg. What is the most likely diagnosis?

• Syndrome of inappropriate ADH secretion (SIADH)

• Acute central diabetes insipidus

• Cerebral salt wasting syndrome

• Adrenal crisis

Answer explanation

This presentation is classic for the second phase of the triphasic response after pituitary stalk injury: SIADH. This phase involves the uncontrolled release of stored ADH, causing hyponatremia and inappropriately concentrated urine.

A 29-year-old female treated for a psychiatric condition develops galactorrhea. Her symptoms mimic the 'stalk effect' seen with pituitary stalk compression. Which medication is the most likely cause?

• Risperidone

• Bromocriptine

• Levodopa

• Lithium

Answer explanation

Risperidone is a potent dopamine (D2) receptor antagonist. By blocking dopamine's tonic inhibitory effect on pituitary lactotrophs, it leads to hyperprolactinemia, causing galactorrhea.

A young adult female with a hemorrhagic sellar mass and hypotension has a serum sodium of 132 mEq/L. What is the primary mechanism for her hyponatremia?

• Impaired free water excretion due to cortisol deficiency

• Syndrome of inappropriate antidiuretic hormone (SIADH)

• Cerebral salt wasting syndrome

• Osmotic diuresis from hyperglycemia

Answer explanation

Cortisol deficiency (secondary adrenal insufficiency) impairs the kidney's ability to excrete free water and also leads to a non-osmotic release of ADH, causing dilutional hyponatremia. This is the key mechanism in this setting.

The patient in the vignette is diagnosed with a pituitary adenoma. The presence of which of the following co-morbidities would be most suggestive of Multiple Endocrine Neoplasia Type 1 (MEN 1)?

• Primary hyperparathyroidism

• Medullary thyroid carcinoma

• Pheochromocytoma

• Cushing's disease

Answer explanation

MEN 1 is characterized by the "3 Ps": Pituitary adenoma, Parathyroid hyperplasia (causing primary hyperparathyroidism), and Pancreatic neuroendocrine tumors. Hyperparathyroidism is the most common manifestation.

A 28-year-old woman presents with a 9-month history of amenorrhea and bilateral galactorrhea. Her serum prolactin level is 220 ng/mL. A subsequent MRI of the brain reveals a 6 mm pituitary microadenoma. What is the most appropriate initial management for this patient?

• Initiation of cabergoline

• Transsphenoidal surgery

• Radiation therapy

• Monthly observation with serial prolactin levels

Answer explanation

Cabergoline, a dopamine agonist, is the first-line medical therapy for symptomatic microprolactinomas. It effectively normalizes prolactin levels, restores gonadal function, and can reduce tumor size.

In the context of the patient described, the absence of the 'posterior pituitary bright spot' on a T1-weighted MRI is primarily due to the depletion of which of the following?

• Arginine vasopressin (AVP) neurosecretory granules

• Pituicytes within the neurohypophysis

• Prolactin-secreting lactotrophs

• Colloid from Rathke's pouch remnants

Answer explanation

The intrinsic hyperintensity (bright spot) of the normal posterior pituitary on T1-weighted images is attributed to the stored phospholipid membranes of neurosecretory granules containing vasopressin. Their absence signifies depletion or destruction.

The ability of the kidneys to excrete a maximal volume of free water is most directly dependent on which physiological parameter?

• The quantity of daily solute excretion

• The glomerular filtration rate (GFR)

• The circulating level of aldosterone

• The renal plasma flow rate

Answer explanation

The kidneys must excrete solutes in a minimum urine osmolality (~50 mOsm/kg). Therefore, the total volume of urine is limited by the total solute load. A low solute load limits the amount of free water that can be excreted.

A man with a history of a recently resected pituitary adenoma presents with lethargy. His labs show TSH 0.1 mU/L (normal: 0.4–4.0) and free T4 0.6 ng/dL (normal: 0.8–1.8). What is the most likely diagnosis?

• Central hypothyroidism

• Subclinical hyperthyroidism

• Primary hypothyroidism

• Graves' disease

Answer explanation

The combination of a low free T4 with an inappropriately low (not elevated) TSH is the hallmark of central hypothyroidism, consistent with his history of pituitary pathology.

A woman at 10 weeks of gestation undergoes routine screening. Her laboratory results show a TSH of 8.4 mIU/L (trimester-specific reference <2.5 mIU/L) and a normal free T4. She is asymptomatic. What is the most appropriate next step?

• Initiate levothyroxine therapy immediately.

• Recheck thyroid function tests in 4 weeks.

• Measure anti-TPO antibody levels before treatment.

• Reassure the patient and monitor clinically.

Answer explanation

Subclinical hypothyroidism in pregnancy (TSH above the trimester-specific upper limit) requires immediate treatment with levothyroxine to mitigate risks of adverse fetal neurodevelopmental outcomes and obstetric complications.