37 Parathyroid Glands

• Calcium is transported in the blood bound to plasma proteins (45%; largely albumin), bound to small anions such as phosphate or citrate (15%), or in the free ionized state (40%).
• Ionized calcium - 4.6 to 5.2 mg/dL
• Total serum calcium - 8.5 to 10.2 mg/dL.

• Parathyroid hormone
• Bone - Stimulates resorption of calcium and phosphate
• Kidney - Stimulates resorption of calcium and conversion of 25(OH)D3; inhibits resorption of phosphate and bicarbonate
• Intestine - No direct effects

• Vitamin D
• Bone - Stimulates transport of calcium
• Kidney - Inhibits resorption of calcium
• Intestine - Stimulates calcium and phosphate absorption

• Calcitonin
• Bone - Inhibits resorption of calcium and phosphate
• Kidney - Inhibits resorption of calcium and phosphate
• Intestine - No direct effects

• Technetium 99m (99mTc) sestamibi scintigraphy has long been used in the evaluation of myocardial perfusion. However, in 1989, it was noted that it had selective affinity for abnormal parathyroid glands because of their abundance of mitochondria.
• Sestamibi is a monovalent, lipophilic cation that passively diffuses across cell membranes and accumulates in mitochondria.

• There are two primary techniques to differentiate sestamibi uptake by abnormal parathyroid and thyroid tissue.
• - The first involves a dual radionuclide approach with sestamibi and either iodine-123 or 99mTc pertechnetate (subtraction imaging)
• - The second uses sestamibi alone with early and delayed imaging (dual phase).

• Sestamibi single photon emission computed tomography, owing to its improved spatial resolution, has become the most commonly used preoperative imaging study in parathyroid disease.
• More recently, sestamibi combined with computed tomography (CT) offers the advantage of detecting smaller parathyroid lesions that would otherwise be undetectable with sestamibi alone. However, the overall sensitivity in detecting small lesions (<500 mg) varies considerably.  Similar to neck ultrasound, the sensitivity of sestamibi is diminished by multiglandular parathyroid disease and concurrent thyroid pathology.

By knowing which of the four parathyroid glands is hyperfunctioning, a surgeon is able to remove only the one parathyroid gland that is producing excessive amounts of parathyroid hormone and no longer under the biochemical control of the body, and leave the other 3 normal parathyroid glands in place. This operation is now termed a "minimally invasive parathyroidectomy".

• Noninvasive -
• 99mTc sestamibi
• Sestamibi SPECT
• Ultrasound
• 4D-CT
• MRI
• PET/CT

• Invasive
• Venous localization
• Ultrasound-guided biopsy

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• o Neuromuscular irritability – laryngospasm, cramping, seizure, peripheral and perioral paresthesia
• o Carpopedal spasm
• o Chvostek’s sign - tapping of facial nerve (tap the Cheek) contraction of facial muscles.
• o Trousseau’s sign - occlusion of brachial artery with BP cuff (cuff the Triceps) - carpal spasm.
• o Erb's sign - electric excitability of the muscles increases.
• o Cardiovascular – QT prolongation

• o Most cases of hypoparathyroidism following thyroid surgery occur within 2-5 days after operation.
• o The symptoms are relieved speedily by slow intravenous infection of 10-20 ml 10% calcium gluconate.
• o 1,25 Dihydroxycholecalciferol can be given orally for long term management because it increases the active absorption of calcium and phosphorous from the gut

• Hypercalcemic crisis (serum calcium >14mg/dl)
• Constitutional (fatigue)
• Neurologic (depression, confusion, obtundation),
• GI (constipation, abdominal pain),
• Renal findings, including insufficiency caused by severe hypovolemia, oliguria/anuria, and hyperkalemia

• Chronic hypercalcemia -
• Nephrolithiasis, Nephrocalcinosis
• Significant bone disease such as osteopenia and
• osteoporosis
• Musculoskeletal abnormalities