Pituitary + Thyroid & Parathyroid

Question 1

Parathyroid glands are embryologically derived from

Accepted Answer

Pharyngeal pouches (3rd and 4th) — Superior parathyroids derive from the 4th pharyngeal pouch, inferior parathyroids from the 3rd pharyngeal pouch (same as thymus). This explains why ectopic parathyroid tissue can be found in the mediastinum alongside ectopic thymic tissue.

Question 2

The predominant cell type in parathyroid glands responsible for PTH secretion is

Accepted Answer

Chief cells — Chief cells are the main PTH-secreting cells. They have pale cytoplasm and round nuclei. Oxyphil cells appear after puberty, have abundant mitochondria, and their function is unclear. Fat cells make up ~50% of normal parathyroid stroma in adults.

Question 3

PTH secretion is directly stimulated by

Accepted Answer

Low serum calcium — The calcium-sensing receptor (CASR) on chief cells continuously monitors serum calcium. When calcium falls, PTH is rapidly released. When calcium rises, PTH secretion is suppressed. This is a direct, rapid feedback loop not mediated by the pituitary.

Question 4

Oxyphil cells are characterized by

Accepted Answer

Abundant mitochondria filling the cytoplasm — Oxyphil cells are large, eosinophilic cells packed with mitochondria — hence their name and pink color on H&E. They appear after puberty and increase with age. They do NOT normally secrete PTH. However, oxyphil cell adenomas CAN cause hyperparathyroidism.

Question 5

PTH increases serum calcium through all of the following EXCEPT

Accepted Answer

Directly increasing intestinal calcium absorption — PTH does NOT directly act on the gut. Its intestinal effect is indirect — PTH stimulates renal 1-alpha hydroxylase → activates vitamin D (calcitriol) → calcitriol then increases intestinal calcium and phosphate absorption. PTH also causes renal phosphate wasting (phosphaturia).

Question 6

The most common cause of primary hyperparathyroidism is

Accepted Answer

Solitary parathyroid adenoma — Solitary adenoma accounts for ~85% of primary HPT. Four-gland hyperplasia = ~15%. Parathyroid carcinoma = <1%. Primary HPT is the most common cause of hypercalcemia in outpatients (vs malignancy = most common in inpatients).

Question 7

Secondary hyperparathyroidism is most often due to

Accepted Answer

Chronic renal failure causing hypocalcemia — CRF mechanism: decreased GFR → phosphate retention (hyperphosphatemia) + decreased 1-alpha hydroxylation of vitamin D → hypocalcemia → all four parathyroid glands undergo compensatory hyperplasia → elevated PTH. This is a REACTIVE (compensatory) process, not autonomous.

Question 8

Tertiary hyperparathyroidism occurs when

Accepted Answer

Chronically hyperplastic parathyroids develop autonomous PTH secretion causing hypercalcemia — After prolonged secondary HPT, one or more hyperplastic glands undergoes monoclonal transformation → autonomous PTH secretion independent of calcium feedback → hypercalcemia develops even after the original cause (e.g. CRF) is corrected (e.g. post-renal transplant). May require parathyroidectomy.

Question 9

Parathyroid carcinoma is associated with mutations in

Accepted Answer

CDC73 gene (parafibromin) — CDC73 (formerly HRPT2) encodes parafibromin, a tumor suppressor. Loss of parafibromin immunostaining on histology supports malignancy. CDC73 germline mutations also cause hyperparathyroidism-jaw tumor syndrome (HPT-JT). Parathyroid carcinoma = very firm, grey-white, adherent to surrounding structures.

Question 10

The classic symptomatic triad of primary hyperparathyroidism is

Accepted Answer

Bones, stones, groans, and psychic moans — Bones (osteitis fibrosa cystica, subperiosteal resorption, brown tumors), Stones (nephrolithiasis — calcium oxalate/phosphate), Groans (peptic ulcers, constipation, nausea — hypercalcemia reduces smooth muscle tone), Psychic moans (depression, confusion, lethargy). Today most cases are asymptomatic, found incidentally.

Question 11

A solitary encapsulated parathyroid nodule with a rim of compressed normal parathyroid tissue at its edge is characteristic of

Accepted Answer

Parathyroid adenoma — The compressed rim of normal tissue at the periphery is the key distinguishing feature of an adenoma vs hyperplasia (where all glands are enlarged with no rim). Adenomas are typically single, weigh 0.5–5g (normal = 35–40mg each), and are composed mainly of chief cells.

Question 12

Water-clear cell hyperplasia refers to

Accepted Answer

Rare form of primary hyperplasia where cells have abundant clear glycogen-rich cytoplasm — Water-clear cell (wasserhelle cell) hyperplasia is a rare form of primary hyperplasia. All four glands are massively enlarged (can reach 10g total). Cells have large, empty-looking cytoplasm due to glycogen and vacuoles. Associated with marked hypercalcemia.

Question 13

The most reliable diagnostic criterion for parathyroid carcinoma is

Accepted Answer

Local invasion into adjacent tissues or distant metastasis — This is the gold standard. Histologic features like nuclear pleomorphism, thick fibrous bands, and mitoses are suggestive but NOT diagnostic alone — they can be seen in benign adenomas. Only unequivocal invasion (into thyroid, vessels, nerves) or metastasis confirms carcinoma. Loss of parafibromin (CDC73) staining supports diagnosis.

Question 14

In primary parathyroid hyperplasia, the combined weight of all four glands typically

Accepted Answer

Exceeds 1g total (normal ~35–40mg each) — Normal total parathyroid weight = ~140–160mg (4 glands × ~35–40mg each). In primary hyperplasia, total gland weight exceeds 1g. In secondary hyperplasia from CRF, combined weight can reach several grams. All four glands are involved though asymmetrically.

Question 15

Oxyphil adenomas are composed of

Accepted Answer

Cells packed with mitochondria giving eosinophilic cytoplasm — Oxyphil adenomas are composed predominantly of oxyphil cells (large, eosinophilic, mitochondria-packed). Despite being composed of cells that don't normally secrete PTH, oxyphil adenomas can still cause hyperparathyroidism — thought to be due to small numbers of functioning chief cells within the tumor.

Question 16

The most common cause of hypoparathyroidism is

Accepted Answer

Inadvertent surgical removal during thyroidectomy or neck surgery — Surgical hypoparathyroidism is most common — inadvertent removal or devascularization of parathyroids during total thyroidectomy, parathyroidectomy, or radical neck dissection. Presents within hours to days post-op with hypocalcemia → perioral tingling, carpopedal spasm, tetany, seizures.

Question 17

Chvostek's sign is elicited by

Accepted Answer

Tapping the facial nerve just anterior to the ear causing ipsilateral facial muscle twitching — Tapping over the facial nerve (CN VII) at the parotid gland → twitching of ipsilateral facial muscles (orbicularis oculi, orbicularis oris, nasalis). Seen in hypocalcemia due to increased neuromuscular excitability. Less sensitive and specific than Trousseau's sign. Can be positive in ~10% of normal individuals.

Question 18

Autosomal dominant hypoparathyroidism is caused by mutations in

Accepted Answer

CASR gene (gain-of-function) — Gain-of-function CASR mutations → receptor is hypersensitive to calcium → PTH suppressed even at normal/low calcium levels → hypocalcemia + hypercalciuria. Autosomal dominant. Treat cautiously — vitamin D/calcium supplementation worsens hypercalciuria and can cause nephrocalcinosis.

Question 19

Autoimmune Polyendocrine Syndrome Type 1 (APS-1) includes all of the following EXCEPT

Accepted Answer

Hypercalcemia — APS-1 (APECED) = AIRE gene mutation (autosomal recessive). Classic triad: Chronic mucocutaneous Candidiasis + Hypoparathyroidism + Adrenal insufficiency (Addison's). Causes HYPOcalcemia (not hypercalcemia) due to hypoparathyroidism. Also: type 1 DM, hypothyroidism, gonadal failure, alopecia, vitiligo.

Question 20

Hypocalcemia in pseudohypoparathyroidism is due to

Accepted Answer

End-organ resistance to PTH due to defective G-protein (Gsα) signaling — Pseudohypoparathyroidism: PTH is ELEVATED (parathyroids work fine and respond to hypocalcemia) but kidneys and bones FAIL to respond → hypocalcemia + hyperphosphatemia despite high PTH. Type 1a = Albright hereditary osteodystrophy (AHO): short stature, round face, short 4th metacarpal, obesity, mental disability. Caused by GNAS mutations.

Question 21

Elevated PTH with hypercalcemia indicates

Accepted Answer

Primary or tertiary hyperparathyroidism — In primary HPT: adenoma/hyperplasia secretes PTH autonomously → both PTH and calcium are elevated. In secondary HPT: PTH elevated but calcium is LOW/normal (reactive). In tertiary HPT: started as secondary but now autonomous → both PTH and calcium elevated (like primary). Malignancy-associated hypercalcemia = PTHrP elevated, PTH suppressed.

Question 22

Hypophosphatemia is characteristic of

Accepted Answer

Primary hyperparathyroidism — PTH causes phosphaturia (renal phosphate wasting) → hypophosphatemia in primary HPT. In CRF-related secondary HPT: phosphate is RETAINED (hyperphosphatemia) because failing kidneys can't excrete it. In hypoparathyroidism: low PTH → phosphate retained → hyperphosphatemia.

Question 23

Calciphylaxis (calcific uremic arteriolopathy) is most commonly associated with

Accepted Answer

Secondary hyperparathyroidism in end-stage renal disease — Calciphylaxis: calcium-phosphate product elevated in CRF → calcium deposits in small vessel walls → ischemic necrosis of skin and subcutaneous fat → excruciatingly painful non-healing skin ulcers. High mortality (~60–80%). Treatment: sodium thiosulfate, wound care, correct calcium-phosphate balance, sometimes parathyroidectomy.

Question 24

Renal osteodystrophy is a complication of

Accepted Answer

Secondary hyperparathyroidism from chronic renal failure — Renal osteodystrophy = complex bone disease in CRF comprising: osteitis fibrosa cystica (from high PTH), osteomalacia (from vitamin D deficiency), osteosclerosis (rugger jersey spine), and adynamic bone disease. Management: phosphate binders, active vitamin D, calcimimetics, dialysis.

Question 25

A prolonged QT interval on ECG is characteristically seen in

Accepted Answer

Hypocalcemia — Hypocalcemia prolongs the action potential plateau phase → prolonged QT interval → risk of ventricular arrhythmias (torsades de pointes). Hypercalcemia SHORTENS the QT interval. Remember: calcium stabilizes cardiac membranes — low calcium = prolonged, unstable; high calcium = shortened, stabilized.

Question 26

MEN1 (menin) mutations are most commonly found in

Accepted Answer

Sporadic parathyroid adenomas (~20–30%) and MEN1-associated adenomas — MEN1 mutations (chromosome 11q13) occur in ~20–30% of sporadic adenomas and in virtually all MEN1-associated parathyroid tumors. MEN1 is a tumor suppressor — loss of both alleles (two-hit hypothesis) required for tumor formation. NOT found in carcinomas (which have CDC73 mutations instead).

Question 27

Hyperparathyroidism-jaw tumor (HPT-JT) syndrome involves germline mutations in

Accepted Answer

CDC73 gene (parafibromin) — HPT-JT syndrome: CDC73 germline mutations → parathyroid tumors (often cystic adenomas, higher risk of carcinoma ~15%) + ossifying fibromas of jaw + renal lesions (cysts, hamartomas, Wilms tumor). Important to recognize because of elevated carcinoma risk vs sporadic HPT.

Question 28

Autosomal dominant hypocalcemia (ADH) is caused by

Accepted Answer

Loss-of-function CASR mutations — Gain-of-function CASR mutations → hypersensitive calcium sensor → PTH suppressed at inappropriately low calcium → hypocalcemia + hypercalciuria (because CASR in kidney also activated → increased urinary calcium excretion). Treat cautiously — aggressive calcium replacement → nephrocalcinosis/nephrolithiasis.

Question 29

Familial isolated hypoparathyroidism (FIH) is linked to mutations in

Accepted Answer

GCM2 gene (glial cells missing 2) — GCM2 is a transcription factor essential for parathyroid gland development. Loss-of-function mutations → absent/hypoplastic parathyroids → isolated hypoparathyroidism (no other endocrine deficiencies, unlike APS-1 or DiGeorge). Can be autosomal dominant or recessive.

Question 30

22q11.2 deletion syndrome (DiGeorge syndrome) causes hypoparathyroidism due to

Accepted Answer

Failed development of 3rd and 4th pharyngeal pouches → absent/hypoplastic parathyroids and thymus — DiGeorge: 22q11.2 deletion → TBX1 gene haploinsufficiency → failed 3rd/4th pharyngeal pouch development → absent parathyroids (hypocalcemia/tetany) + absent thymus (T-cell immunodeficiency) + conotruncal cardiac defects. CATCH-22: Cardiac defects, Abnormal facies, Thymic hypoplasia, Cleft palate, Hypocalcemia, 22q11.

Question 31

First-line management of asymptomatic primary hyperparathyroidism without meeting surgical criteria is

Accepted Answer

Observation with monitoring of calcium, renal function, and bone density — Surgical criteria (any one): calcium 0.25mmol/L above upper normal, age <50, eGFR <60, T-score <−2.5 or fragility fracture, 24hr urine calcium 400mg. If none met → watchful waiting: annual calcium/creatinine, 1–3 yearly DEXA scan. Avoid thiazides, lithium, immobilization, high calcium diet.

Question 32

Calcimimetics like cinacalcet work by

Accepted Answer

Allosterically enhancing CASR sensitivity to calcium → suppressing PTH secretion — Cinacalcet is a positive allosteric modulator of CASR → CASR more sensitive to calcium → PTH secretion is suppressed. Used in secondary hyperparathyroidism of CKD and parathyroid carcinoma.

Question 33

Hypercalcemia associated with malignancy is typically due to

Accepted Answer

Overproduction of PTHrP by the tumor — Humoral hypercalcemia of malignancy (HHM) is most commonly caused by PTHrP secretion (80% of cases). Direct bone lysis by metastases accounts for ~20%. True parathyroid adenoma causing hypercalcemia in a cancer patient is rare. PTH is suppressed in HHM.

Question 34

A patient with severe hyperparathyroidism undergoing parathyroidectomy suddenly develops tetany and carpopedal spasm post-operatively. This is most consistent with

Accepted Answer

Hypocalcemia due to hungry bone syndrome — Hungry bone syndrome occurs post-parathyroidectomy in patients with severe HPT and high bone turnover. The abrupt removal of PTH leads to rapid bone mineralization, causing a precipitous drop in serum calcium. Tetany and carpopedal spasm are classic signs of hypocalcemia.

Question 35

In secondary hyperparathyroidism due to chronic renal failure, PTH levels are usually

Accepted Answer

Markedly elevated — Chronic renal failure leads to phosphate retention and impaired vitamin D activation, causing hypocalcemia. This chronically stimulates the parathyroid glands, leading to compensatory hyperplasia and markedly elevated PTH levels.

Question 36

Brown tumors of bone are characteristic of

Accepted Answer

Primary hyperparathyroidism — Brown tumors are accumulations of osteoclasts, reactive giant cells, and hemorrhage due to excessive bone resorption driven by high PTH levels in primary hyperparathyroidism (osteitis fibrosa cystica).

Question 37

Familial hypocalciuric hypercalcemia (FHH) is characterized by

Accepted Answer

A low calcium-to-creatinine clearance ratio — FHH is caused by inactivating mutations in the calcium-sensing receptor (CASR), leading to reduced sensitivity to calcium. This results in a higher set point for PTH secretion, causing hypercalcemia with inappropriately normal or mildly elevated PTH. Crucially, urinary calcium excretion is low due to impaired sensing in the renal tubules, leading to a low Ca:Cr clearance ratio.

Question 38

Which of the following is NOT a classic feature of MEN1 syndrome?

Accepted Answer

Pheochromocytomas — MEN1 classically involves tumors of the parathyroid glands (most common), pituitary gland, and pancreas (gastrinomas, insulinomas, etc.). Adrenal adenomas can occur, but pheochromocytomas are characteristic of MEN2.

Question 39

The primary mechanism by which PTH increases serum calcium is by

Accepted Answer

Increasing bone resorption and decreasing renal excretion of calcium — PTH primarily increases serum calcium by stimulating osteoclast-mediated bone resorption and by increasing calcium reabsorption in the distal tubules of the kidney. Its effect on intestinal absorption is indirect, via vitamin D activation.

Question 40

A patient with chronic renal failure develops hyperphosphatemia. This is because the failing kidneys are unable to

Accepted Answer

Excrete phosphate — Healthy kidneys filter and excrete phosphate. In chronic renal failure, this filtration capacity is reduced, leading to phosphate retention (hyperphosphatemia). This also contributes to hypocalcemia, which stimulates PTH secretion.

Question 41

Which parathyroid hormone-related condition is most often associated with a significantly increased risk of parathyroid carcinoma?

Accepted Answer

Hyperparathyroidism-jaw tumor (HPT-JT) syndrome — HPT-JT syndrome, caused by CDC73 gene mutations, carries a substantially higher risk of parathyroid carcinoma (around 15%) compared to sporadic adenomas (<1%) or MEN1.

Question 42

In hypoparathyroidism, the characteristic electrolyte abnormalities are:

Accepted Answer

Hypocalcemia, hyperphosphatemia — Lack of PTH leads to decreased calcium reabsorption in the kidneys and decreased bone resorption, resulting in hypocalcemia. It also leads to decreased phosphate excretion, causing hyperphosphatemia.

Question 43

The Ellsworth-Howard test is used to differentiate between hypoparathyroidism and

Accepted Answer

Pseudohypoparathyroidism — The Ellsworth-Howard test involves infusing PTH and measuring urinary cAMP and phosphate. In hypoparathyroidism, PTH is absent, so the infusion causes a rise in cAMP and phosphate. In pseudohypoparathyroidism, PTH is present but the kidneys are resistant, so there is no significant rise in cAMP or phosphate.

Question 44

Which of the following is the MOST likely cause of hypercalcemia in a patient with known advanced lung cancer?

Accepted Answer

Overproduction of PTHrP by the tumor — Humoral hypercalcemia of malignancy, typically caused by PTHrP secretion, is the most common mechanism for hypercalcemia in cancer patients, particularly those with squamous cell carcinoma of the lung. PTH levels would be suppressed in this scenario.

Question 45

Thyroid surgery may lead to hypoparathyroidism if:

Accepted Answer

The parathyroid glands are inadvertently removed or devascularized — The parathyroid glands are located anatomically close to the thyroid gland. During thyroid surgery, they can be accidentally removed or their blood supply compromised, leading to hypoparathyroidism and subsequent hypocalcemia.

Question 46

In primary hyperparathyroidism, the serum calcium level is typically elevated because:

Accepted Answer

Bone resorption is increased, and renal calcium reabsorption is enhanced — Elevated PTH in primary hyperparathyroidism leads to increased release of calcium from bone (resorption) and increased reabsorption of calcium in the renal tubules, both contributing to hypercalcemia.

Question 47

Calcification in the lungs, blood vessels, and periarticular soft tissues is a hallmark of:

Accepted Answer

Metastatic calcification secondary to chronic hyperphosphatemia (e.g., in CRF) — When the calcium-phosphate product is significantly elevated (typically 55-60 mg²/dL²), calcium phosphate can precipitate in various tissues, leading to metastatic calcification. This is common in conditions like chronic renal failure with secondary hyperparathyroidism.

Question 48

What is the typical PTH level in Familial Hypocalciuric Hypercalcemia (FHH)?

Accepted Answer

Normal or mildly elevated — In FHH, the calcium-sensing receptor (CASR) is less sensitive to calcium. Consequently, higher calcium levels are required to suppress PTH. Therefore, PTH is inappropriately normal or mildly elevated for the degree of hypercalcemia, rather than being suppressed as seen in primary hyperparathyroidism.

Pituitary + Thyroid & Parathyroid

Questions, Answers & Explanations