Parathyroid

Question 1

What is the parathyroid derived from?

Answer 1

pharyngeal pouches

-could be found in the carotid sheath, thymus and anterior mediatinum

Question 2

Parathyroid histology

Answer 2

Chief cells predominate and contain glycogen and produce PTH

Oxyphil cells in small clusters, packed with mitochondria

-Fat increases with age up to 25 years, occupies 30% of adult gland

Question 3

What does PTH do?

Answer 3

1. Activates osteoclasts by mobilizing calcium from bone
   - increased tubular reabsorption
   - increases conversion of vitamin D to active form
   - decreases serum phosphate by increasing urinary excretion
   - Augments GI calcium absorption

-Net effect increase calcium which has negative feedback on PTH

Question 4

What is the most common cause of clinically apparent hypercalcemia? incidental hypercalcemia?

Answer 4

clinically apparent:
malignancy

incidental:
primary hyperparathyroidism

Question 5

Hypercalcemia of Malignancy

Answer 5

Osteolytic metastases: 
tumor
cytokines
local osteolysis
maturation of osteoclasts 

-prognosis is poor, patients present at advanced stage

Question 6

Primary Hyperparathyroidism

age group

Answer 6

50 years old
Sporadic or familial 
1. Parathyroid adenoma (85-95%)
2. Primary Hyperplasia (diffuse or nodular) 5-10%
3. Parathyroid carcinoma 1%

Question 7

Familial primary hyperparathyroidism
MEN1
MEN2A
Familail hypocalciuric hypercalcemia

Answer 7

1. MEN 1-inactivation of MEN1 gene on chromosome 11q13 (tumor suppressor gene)
2. MEN2A-activating mutation of RET (tyrosine kinase receptor) gene on chromosome 10q
3. familial hypocalciuric hypercalcemia-autosomal dominant disorder due to mutation in parathyroid calcium-sensing receptor gene (CASR) on chromosome 3

Question 8

Parathyroid adenoma

Answer 8

Gross
-solitary
-increased uptake of radionuclide scan
.5-5 gm

Histology:
Sheets or nests of chief cells or oxyphil cells
Encapsulated lesion with compressed normal rim of parathyroid at pituitary
Mitotic figures rare
May find endocrine atypia-rep degenerative change-not a criteria for malignancy
-

Question 9

Parathyroid hyperplasia

Answer 9

2-4 glands
combined weight 1 gm
microscopically diffuse or multinodular chief cell hyperplasia most common

Question 10

Parathyroid carcinoma

Answer 10

Gross:
solitary mass, may exceed 10gm
-may be circumscribed lesion or clearly invasive neoplasm

Histo:
Cells resemble normal parathyroid and are arranged in trabeculae or nodules with dense fibrous capsule with intervening fibrous bands

Diagnosis: local invasive of surrounding tissue and metastasis

Question 11

Osteitis fibrosa cystica

Answer 11

thinned bony cortex with marrow containing fibrous tissue, hemorrhages and cyst formation

Question 12

Brown tumor

Answer 12

collection of osteoclasts, reactive giant cells and hemorrhage debris forming masses that stimulate tumor

Question 13

Kidney changes from hyperparthyroidism

Answer 13

1. formation of stones
2. calcification of interstitium and tubules
3. metastatic calcification in organs like stomach, lung, myocardium or blood vessels

Question 14

Primary Hyperparathyroidism

clinical manifestations

Answer 14

May be asymptomatic and identified by hypercalcemia on routine exam

bone, stones, groan, psychiatric undertones

Question 15

Secondary Hyperparathyroidsim

Etiology

Answer 15

-process of chronic depression or decrease in calcium that causes compensatory overactivity of the parathyroid glands

• -Renal Failure most common
  1. decreased phosphate excretion-hyperphosphatemia-decreases serum calcium-parathyroid stimulation
  2. deficiency of alpha1 hyodroxylase–deficiency of Vitamin D-less absorption of clcium from GI tract and eventually parathyroid stimulation

0ther eitologies-decreased dietary Ca, steatorrhea, vit D def

Question 16

Secondary Hyperparathyroidsim

Clinical features

Answer 16

• skeletal changes not as severe as in primary hyperparathyroidism
• vascular calcification may cause significant ischemic damages to skin-calciphylaxis

Question 17

Tertiary hyperparathyroidsim

Answer 17

MInority of patients-autonomous hyperparathyroidism with symptomatic hypercalcemia

-parathyroidectomy necessary for controlling symptoms

Question 18

Hypoparathyroidism

Etiology

Answer 18

Less common than hyper
Etiology:
1. Surgically induced

2. Autoimmune
   - mucocutaneous candidiasis
   - adrenal insufficiency (autoimmune polyendocrine syndrome 1 APS1)
3. Autosomal dominant hypoparathyroidism-gain of function mutation in calcium sensing receptor gene (CASR)-hypercalcemia and hypocalcemia
4. Familial isolated hypoparathyroidism-rare disorder due to the encoding PTH precursor peptide
5. Congenital absence of parathyroid-DiGeorge or 22q11

Question 19

Hypoparathyroidism CLinical manifestations

Answer 19

1. Tetany-numbness, paresthesias, carpopedal spasm, laryngospasm, seizures
2. chvostek sign-occude circulation in forearm, observe carpal spasm
3. mental status changes-emotional instability, anxiety, depression, confusion, hallucinations and frank psychosis
4. Intracranial manifestations-calcifications of basal ganglia, parkinson like movement disorders and increased intracranial pressure with papilledema
5. ocular disease-catarct formation
6. cardiovascular manifestation*******-Prolonged QT interval
7. Dental abnormalities-dental hypoplasia, failure of eruption, defective enamel and root formation and carious teeth

Question 20

Pseudohypoparathyroidism

Answer 20

Rare disease due to end organ resistance to the actions of PTH
-increased to normal PTH with hypocalcemia