Parathyroid Review

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Anatomy

From the 3rd and 4th pharyngeal pouches

3rd pouch is associated with inferior parathyroid and thymus

  • Found anteromedially

  • More likely to be ectopic 🡪 tail of thymus (MC), intrathyroid, mediastinum

4th pouch is associated with superior parathyroid and thyroid complex

  • Found posterolaterally

Inferior thyroid artery supplies both superior and inferior parathyroids

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Hormones

PTH

Increases calcium via:

  • Kidney reabsorption in DCT

  • Increase osteoclast activity in bone 

  • Increase Vit D production in kidney (1-OH) 🡪 increase calcium binding in intestine

Also increase PO4- excretion

Vit D

Increases Ca++ AND PO4- via intestine absorption

Calcitonin

Decrease calcium (INHIBITS OSTEOCLASTS)

Increase urinary Ca++ and PO4- excretion

Hyperparathyroidism

 
 

Primary

Symptoms reflect changes associated with an increase in calcium

Causes:

Single Adenoma (80%) 🡪 resection

Multiple Adenoma (4%) 🡪 resection 

Hyperplasia (15%): Men I and IIa have 4 gland hyperplasia 🡪 subtotal or total + re-implantation

***Adenocarcinoma - rare; can have very high calcium -> radical parathyroidectomy + ipsilateral thyroid lobectomy

 

** preg: 2nd trimester

** pre-op PTH 🡪 should be ½ of pre-op PTH

** if missing check: “normal” spot, thymus, trachea-esophageal groove, carotids, vertebral body, superior pharynx, thyroid

If still missing🡪 sestamibi scan

Persistent hyperparathyroidism🡪 missed adenoma

Recurrent hyperparathyroidism 🡪 new adenoma vs tumor implants

** reop🡪 higher risk of injury

Secondary and Tertiary

2°

Increased PTH 2/2 low Ca (ie in renal failure)

TX: Ca, Vit D, PO4 binder (sevelamer), Cinnacalcet (mimics Ca)// Surgery for bone pain, fx, and pruritus (total + reimplant)

 

3°

Persistently increased PTH despite “fixing” renal issues

TX: subtotal or total + reimplant

 
The above is from radiopedia.org

The above is from radiopedia.org

 

The sestamibi scan is a nuclear medicine study that utilizes Technicium-99-sestamibi. This radio-isotope is taken up by a hyperfunctioning parathyroid gland, and helps with localization.

Special Parathyroid Cases

 

Pseudo - hypoparathyroidism

  • Defective PTH receptor in kidney; no response to PTH

 
 

Hypercalcemia

  • 90% from hyperplasia/ cancer

  • Other reasons include: hyperthyroidism, granulomatous disease, Vit D overdose, milk alkali syndrome (high milk/supplement intake), thiazides, 

Treatments:

  • Fluid resuscitation

  • Calcitonin

  • Bisphosphonate (does not work immediately)

  • Steroids (esp if etiology is cancer/granulomatous disease)

  • *****dialysis if severe******

**Malignancies**

  • Hematologic (25%) - lytic lesions, low urinary Ca. Ex: multiple myeloma

  • Non-hematologic (75%) - PTHrP; high urinary Ca. Ex: Squam lung Ca, Breast

 

Familial Hypercalcemia Hypocalciuria

  • Increased SERUM calcium. Decreased URINE calcium 

  • 2/2 to defective PTH receptor in distal convoluted tubule

  • TX: nothing. NO parathyroidectomy

 
 

Multiple Endocrine Neoplasia

 
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MEN I

  • Menin

  • chromosome 11q3

  • Parathyroid most common, typically presenting symptom

  • Pancrease: MC -> gastrinoma; correcting hypercalcemia from hyperparathyroidism may correct this

  • Pituitary

  • Correct parathyroid 1st

MEN IIa/b

  • Ret - protooncogene/MTKR

  • MTC nears 100%

  • Pheo is typically b/l + benign

  • IIB is Badder (B) than IIa

Treatment

  • Pheo 1st

  • MTC nears 100%: Prophylactic removal at 6yo (IIa)/ 2yo (IIb)

 

Parathyroid Cancer

  • Increase Ca (in the 13’s/14’s) , PTH, and alk phos

  • Lung mets

  • Mortality is 2/2 to hypercalcemia. Recur in 50%. MANAGE HYPERCALCEMIA

  • 50% 5 yr mortality

  • TREATMENT:

    Parathyroidectomy + ipsilateral thyroidectomy