Parathyroid

High Yield Anatomy and Physiology

• What is the relationship of the parathyroid glands and the recurrent laryngeal nerve?
• Superior parathyroids are posterior and lateral to RLN
• Originate from 4th pharyngeal pouch
• Inferior parathyroids are anterior and medial to RLN
• Originate from 3rd pharyngeal pouch
• Inferior glands more variable
• Thymus also migrates with 3rd pharyngeal pouch
• Inferior thyroid artery provides blood supply to all 4 glands in 80% of cases
• What cells release parathyroid hormone (PTH), and what is the stimulus?
• PTH released from chief cells in parathyroid in response to low Ca levels
• What cells release calcitonin and what is the stimulus?
• Calcitonin is released from parafollicular c-cells in the thyroid in response to high calcium
• What are the actions of PTH on bone and in the kidney?
• Bone – Stimulates osteoclasts for resorption of Ca and phosphate
• Kidneys - Stimulates resorption of Ca, inhibits resorption of phosphate and bicarb, Stimulates conversion of 25(OH)D3 to 1,25(OH)2D3 via 1-alpha hydroxylase (phosphate trashing hormone)
• How does Vit D (1,25OH2D3) increase serum Ca?
• Stimulates absorption of Ca and Phosphate in gut
• How does Calcitonin decrease serum Ca in the bone and the kidney?
• Bone – Inhibits osteoclast bone resorption
• Kidney - Inhibits resorption of Ca and phosphate

Figure 1: Parathyroid Hormone Physiology

• What is the most common cause of hypercalcemia in the outpatient and inpatient setting?
• Outpatient = primary hyperparathyroidism
• Inpatient = Malignancy
• What is the mechanism of hypercalcemia due to malignancy?
• MCC hypercalcemia 2/2 malignancy is production of PTH related protein (e.g. Squamous cell lung CA, Breast CA)
• Lytic bone lesions are less common malignant cause of hypercalcemia
• What is the treatment of a hypercalcemic crisis?
• Treat with fluids (normal saline around 300ml/hr) and lasix once patient is euvolemic . Initially just saline . Why not LR?
• LR has calcium
• What . are the most common causes of primary

hyperparathyroidism?

• Adenoma (80-90%; 2-5% have double adenoma)
• Hyperplasia (10-15%)
• Parathyroid CA (<1%), MEN 1 and 2A
• What are the laboratory tests used to diagnose hyperparathyroidism?
• Increased Ca (24-hour collection), Decreased Phos (except with renal failure)
• Elevated serum PTH (normal 5-40 pg/dL)
• Chloride to Phosphate ratio >33 (Very specific)
• Increased Urinary Ca, Increased urinary cAMP Chloride/Phos ratio > 33 is a reliable way to diagnose hyperparathyroidism and frequently tested.
• What studies can be used to localize an adenoma?
• Non-invasive - U/S, sestamibi, Single photon emission CT (SPECT), MRI
• Best is likely sestamibi with SPECT + U/S
• Invasive - angiography with venous sampling for PTH gradients
• Reserved for re-operative cases
• What is the treatment for hyperparathyroidism and who should undergo treatment?
• Parathyroidectomy is only long-term treatment for HPT
• Clear evidence that symptomatic patients should undergo surgery
• What are the indications for asymptomatic patients to undergo parathyroidectomy?
• Elevation of Serum Ca 1 mg/dL or more over normal value
• Decreased Cr Clearance (<60mL/min)

• T-score < -2 .5

• Poor access to care/follow-up
• Age <50
• Some argue all patients with HPT should get surgery
• How do you confirm adequate intraoperative resection of a parathyroid adenoma?
• Measure intraoperative rapid PTH assay - Need 50% drop
• How do you treat multi-gland parathyroid disease
• subtotal parathyroidectomy (3 .5 glands) or total parathyroidectomy with reimplantation into SCM or brachioradialis
• In what patients do you see secondary hyperparathyroidism and what is the treatment?
• In patients with renal failure
• Treat with Ca/Vit D supplements, renal diet, phosphate binders
• In what patients do you see tertiary hyperparathyroidism and what is the treatment?
• Continued high production of PTH despite renal transplant
• Tx: subtotal parathyroidectomy or subtotal with auto- transplantation
• In what patients would you be concerned for parathyroid cancer and what is the treatment?
• Generally, have very high calcium levels, may have palpable mass .
• Rare cause of hyperparathyroidism
• Tx: En bloc resection with ipsilateral thyroid and central neck dissection
• Recurrence/Metastasis treated with palliative surgery, calcium lowering drugs (bisphosphates/calcimimetics) . Chemorads rarely effective .

Quick Hits

• A patient with high-normal range serum Ca with elevated PTH and evidence of bone loss, what is the diagnosis?
• Normocalcemic hyperparathyroidism
• Early form of primary HPT
• Surgery if symptomatic
• What are the electrolyte disturbances found with hyperparathyroidism:
• Hyperchloremic metabolic acidosis
• d/t PTH effect on bicarb excretion in kidney
• Hypophosphatemia
• However, with significant renal impairment, phosphate may be elevated
• A patient with elevated PTH, elevated Ca, Low urinary Ca, what is the diagnosis and treatment?
• Benign Familial Hypocalciuric Hypercalcemia
• Tx? Nothing
• The inferior thyroid artery supplies parathyroid gland laterally or medially?
• Medially
• During a neck exploration for hyperparathyroidism you find 3 normal glands and missing superior gland, where should you look next?
• Check retroesophageal space and open carotid sheath
• During a neck exploration and you find 3 normal glands and missing inferior gland, where should you look next?
• Check ipsilateral side of mediastinal thymus, consider intra- thyroid gland
• You find 4 normal appearing glands with elevated PTH?

• Consider hypersecreting, supernumerary parathyroid gland most commonly located in thymus thymectomy

• Where is the most common location of a missed gland?
• NORMAL anatomic position
• Where is the most common location of an ectopic gland?
• Thymus

Figures