Endocrinology: Pathology - Thyroid and parathyroid disorders

Question 1

Which cells secrete parathyroid hormone?

Answer 1

Chief cells

Question 2

Four functions of parathyroid hormone

Answer 2

1. Increases renal tubular absorption of calcium
2. Increases urinary phosphate excretion
3. Increases conversion of vitamin D to active form in kidneys
4. Augments GI absorption of calcium

Question 3

What is the effect of calcium on parathyroid hormone release?

Answer 3

Inhibits

Question 4

What is the most common cause of asymptomatic hypercalcaemia?

Answer 4

Primary hyperparathyroidism (of which parathyroid adenoma is the most common cause)

Question 5

What is the most common cause of symptomatic hypercalcaemia?

Answer 5

Malignancy

Question 6

How does malignancy increase serum Ca2+?

Answer 6

Either through direct osteolysis by bony metastases, or release of PTH-related peptide

Question 7

What is the mechanism of action of PTHrP?

Answer 7

Promotes RANKL expression which induces osteoclast differentiation

Question 8

Three causes of primary hyperparathyroidism from most to least common

Answer 8

1. Adenoma (85-95%)
2. Parathyroid hyperplasia (diffuse or nodular; 5-10%)
3. Parathyroid carcinoma (1%)

Question 9

Four causes of secondary hyperparathyroidism. Which of these is most common

Answer 9

1. Renal failure (most common)
2. Dietary calcium deficiency
3. Vitamin D deficiency
4. Malabsorption (steatorrhoea)

Question 10

What is the difference in laboratory values seen in primary vs secondary hyperparathyroidism?

Answer 10

Primary: high PTH, normal to high serum Ca2+
Secondary: low to undetectable PTH, high serum Ca2+

Question 11

What clinical presentation is seen with hyperparathyroidism? Which symptoms are most directly related to PTH and which are attributable to hypercalcaemia?

Answer 11

Primary hyperparathyroidism often presents as asymptomatic hypercalcaemia

If symptomatic, presents with “painful bones, renal stones, abdominal groans, and psychic moans”:
1. Bone disease* (osteoporosis, fractures)
2. Nephrolithiasis*
3. GI disturbance (constipation, nausea, peptic ulcers, pancreatitis, gallstones)
4. CNS alterations (depression, lethargy, seizures)
5. Neuromuscular abnormalities (weakness, fatigue**)
6. Cardiac manifestations (aortic and mitral valve calcifications)

• related to PTH
  ** related to hypercalcaemia

Question 12

Two causes of hypercalcaemia with raised PTH

Answer 12

1. Hyperparathyroidism (primary, secondary, or tertiary)
2. Familial hypocalciuric hypercalcaemia

Question 13

Five causes of hypercalcaemia with decreased PTH

Answer 13

1. Hypercalcaemia of malignancy
2. Vitamin D toxicity
3. Thiazide diuretics
4. Immobilisation
5. Granulomatous disease (sarcoidosis)

Question 14

What is the most common cause of hypoparathyroidism?

Answer 14

Surgical removal (including inadvertent during thyroidectomy or radical neck dissection for malignancy)

Question 15

Six symptoms of hypocalcaemia

Answer 15

1. Tetany: circumoral numbness, paraesthesias, carpopedal spasm, laryngospasm, seizure, Chvostek and Trosseau signs
2. Mental status changes: emotional lability, confusion, psychosis
3. Intracranial manifestations: Parkinsonism, basal ganglia calcification, raised ICP
4. Ocular disease: cataracts, lens calcification
5. QTc prolongation
6. Dental abnormalities in early development

Question 16

What is Chvostek sign?

Answer 16

Tapping facial nerve elicits twitching of ear, nose or mouth
Due to hypocalcaemia

Question 17

What is Trosseau sign?

Answer 17

Occlusion of circulation to forearm results in carpal spasm
Due to hypocalcaemia