endocrine-parathyroid

Question 1

Location of parathyroid gland

Answer 1

variably located at the back of thyroid gland

Question 2

Where do parathyroid glands come from?

Answer 2

pharyngeal pouch

Question 3

Weight of each gland?

Answer 3

35-40mg

Question 4

What does each gland comprise of?

Answer 4

chief cells-secrete PTH

oxyphil cells

Question 5

What are the effects of PTH secretion?

Answer 5

Essentially decreased levels of calcium stimulate PTH hormone and cause

• Increase in renal tubular reabsorption of calcium
• Increase in urinary phosphate excretion, thereby lowering serum phosphate levels (since phosphate binds to ionized calcium)
• Increase in the conversion of vitamin D to its active dihydroxy form (1,25 dihydroxy vit D) in the kidneys, which in turn augments
gastrointestinal calcium absorption
• Enhancement of osteoclastic activity (i.e., bone resorption, thus releasing ionized calcium), mediated indirectly by promoting the differentiation of osteoclast
progenitor cells into mature osteoclasts

Question 6

What is another name for 1,25 dihydroxyvitamin D?

Answer 6

calcitriol

Question 7

What are the steps to make calcitriol?

Answer 7

Vitamin D is converted to calcidiol in the liver and then calcitriol in the kidney

Calcidiol acts on kidney and causes calcium reabsorption

Caltitriol acts on SI reabsorption of dietary calcium

Question 8

Classify hyperparathyroidism

Answer 8

Primary
Secondary
Tertiary

Question 9

Describe causes of primary hyperparathyroidism

Answer 9

•Primary (overproduction of PTH)
•Important cause of hypercalcaemia
1.Adenoma: 75-80%
Solitary, 0.5-5grm, well circumscribed, delicate capsule, other glands normal size / shrunken
2.Primary hyperplasia: 10-15%
Diffuse or nodular
Occur sporadically or as a component of MEN syndromes
3.Parathyroid carcinoma: <5%
Diagnosis made on invasion of surrounding tissue and metastasis

Question 10

Describe secondary hyperparathyroidism

Answer 10

Any condition associated with a chronic decreased level of calcium leading to compensatory over activity of the parathyroid gland
Most common cause – renal failure
Chronic renal insufficiency -> ↓PO4 excretion -> hyperphosphataemia -> depress Ca levels -> stimulates parathyroid gland activity (hyperplasia of parathyroid glands) -> increased PTH secretion -> serum calcium remains near normal.
Another: Vit D deficiency

Question 11

Describe tertiary hyperparathyroidism

Answer 11

In a minority of patients, parathyroid activity becomes autonomous and excessive with resultant hypercalcaemia. Hyperplasia of glands due to chronic secondary hyperparathyroidism
- Can be treated with parathyroidectomy.

Question 12

What are the symptoms of hypercalcaemia?

Answer 12

painful bones, renal stones, abdominal groans, psychic moans

osteoporosis , osteitis fibrosis cystica
renal stones; renal insufficiency; polyuria
naseau,vomiting,constipation, PUD, pancreatitis, anorexia
weakness and fatigue
altered concentration, depression, confusion, seizures
mitral and aortic calcifications, heart block, hypertension ;
(Cardiac manifestations)

Question 13

What treatment and investigation can be done for parathyroidism?

Answer 13

Lithium treatment, thiazide diuretics
imaging- U/S and sestamibi scan
Sestamibi allows intraop Gamma probe confirmation ; 91% specific

Question 14

What is the epidemiology a/w hyperpaprathyroidism?

Answer 14

occurs in females more

1:1000 prevalence

Question 15

What are the causes of hypoparathyroidism

Answer 15

•Surgical removal (inadvertently) during thyroidectomy – mistaken for lymph nodes
•Congenital absence (DiGeorge syndrome – along with thymic aplasia)
•Primary idiopathic atrophy (autoimmune) – antibodies against the Ca sensing receptors in parathyroid gland
•Familial hypoparathyroidism
–Condition presents in childhood

Question 16

Signs of hypocalcaemia

Answer 16

–Numbness and tingling in the extremities and perioral region
–Muscle cramps
-Bronchospasm/laryngospasm/seizures
–Chvostek’s sign (muscle spasms of mouth/eye/nose with tapping of the facial nerve)
–Trousseau’s sign (carpal spasm with inflation of sphygmomanometer 20mmHg above systolic pressure)
–Cataract formation (calcification of lens)
–Intra-cranial manifestations (parkinsonian like movement)
–Cardiovascular manifestations – conduction defect with prolonged QT interval

Question 17

Define MEN syndrome

Answer 17

familial diseases (AD) that are a/w hyperplasia and neoplasia of several endocrine organs

Type 1 (Werners syndrome) 
Type 2 A & 2 B

Question 18

What is the most common manifestation for Werners syndrome?

What organs does it commonly affect?

Answer 18

primary hyperparathyroidism

3P’s

• pancreatic islet cells
• parathyroid gland
• pituitary

Question 19

What is the genetic defect a/w Werners

Answer 19

TSG (MEN gene1) located chromosome 11q13

Question 20

Explain type 2

Answer 20

two distinct groups (a&b) that have mutations in RET proto oncogenes located on chromosome 10q11.2

Question 21

What is another name for type 2A and what is the outcome?

Answer 21

Sipple syndrome

medullary carcinoma
phaeochromocytoma
parathyroid hyperplasia

Question 22

Explain what Type 2B is characterized by

Answer 22

medullary carcinoma
phaeochromocytoma
extraendocrine manifestations: 
-ganglioneuromas at mucosal sites 
-marfanoid habitus- long bones of axial skeleton

Question 23

Is type 2B a/w primary hyperparathyroidism?

Answer 23

NO

Question 24

General characteristics of MEN syndrome

Answer 24

• tumors occur at a younger age than compared w sporadic
• occurs in multiple endocrine organs
• multifocal
• tumors preceeded by an asymptomatic period of endocrine hyperplasia
• agressive and higher rate of recurrence than in sporadic tumors

Question 25

What is recommended for pts carrying germline RET mutation?

Answer 25

prophylactic thryroidectomy- to prevent medullary carcinomas