Superior parathyroids – 4th pharyngeal pouch; associated with thyroid complex

•  Found lateral to recurrent laryngeal nerves (RLNs), posterior surface of superior portion of gland, above inferior thyroid artery

  Inferior parathyroids – 3rd pharyngeal pouch; associated with thymus

•  Found medial to RLNs, more anterior, below inferior thyroid artery

•  Inferior parathyroids have more variable location and are more likely to be ectopic

•  Occasionally are found in the tail of the thymus (most common ectopic site) and can migrate to the anterior mediastinum

•  Other ectopic sites – intra-thyroid, mediastinal, near tracheoesophageal groove

  90% have all 4 glands

  Inferior thyroid artery – blood supply to both superior and inferior parathyroid glands

  PTH – increases serum Ca

•  ↑ kidney Ca reabsorption in the distal convoluted tubule, ↓ kidney PO₄ absorption

•  ↑ osteoclasts in bone to release Ca (and PO₄⁻)

•  ↑ vitamin D production in kidney (↑ 1-OH hydroxylation) → ↑ Ca-binding protein in intestine → ↑ intestinal Ca reabsorption

  Vitamin D – ↑ intestinal Ca and PO₄ absorption by increasing calcium-binding protein

  Calcitonin – decreases serum Ca

•  ↓ bone Ca resorption (osteoclast inhibition)

•  ↑ urinary Ca and PO₄ excretion

  Normal Ca level: 8.5–10.5 (ionized 4.4–5.5)

  Normal PTH level: 5–40 pg/mL

  Normal PO₄ level: 2.5–5.0

  Normal Cl⁻ level: 98–107

  Most common cause of hypoparathyroidism is previous thyroid surgery

PRIMARY HYPERPARATHYROIDISM

  Women, older age

  Due to autonomously high PTH

  Dx: ↑ Ca, ↓ PO₄⁻; Cl⁻ to PO₄⁻ ratio > 33; ↑ renal cAMP; HCO₃⁻ secreted in urine

  Can get hyperchloremic metabolic acidosis

  Osteitis fibrosa cystica (brown tumors) – bone lesions from Ca resorption; characteristic of hyperparathyroidism

  Most patients have no symptoms – ↑ Ca found on routine lab work for some other problem or on checkup

  Symptoms: muscle weakness, myalgia, nephrolithiasis, pancreatitis, PUD, depression, bone pain, pathologic fractures, mental status changes, constipation, anorexia

  Hypertension can result from renal impairment

  Indications for surgery:

•  Symptomatic disease

•  Asymptomatic disease with Ca > 13, ↓ Cr clearance, kidney stones, substantially ↓ bone mass

  Single adenoma – occurs in 80% of patients

  Multiple adenomas – occur in 4% of patients

  Diffuse hyperplasia – occurs in 15%; patients with MEN I or IIa have 4-gland hyperplasia

  Parathyroid adenocarcinoma – very rare; can get very high Ca levels

  Treatment

•  Adenoma – resection; inspect other glands to rule out hyperplasia or multiple adenomas

•  Parathyroid hyperplasia

•  Do not biopsy all glands → risks hemorrhage and hypoparathyroidism

•  Tx: resect 3½ glands or total parathyroidectomy and autoimplantation

•  Parathyroid CA → need radical parathyroidectomy (need to take ipsilateral thyroid lobe)

•  Pregnancy – surgery in 2nd trimester; ↑ risk of stillbirth if not resected

  Intraop frozen section → can confirm that the tissue taken was indeed parathyroid

  Intraop PTH levels → can help determine if the causative gland is removed (PTH should go to < ½ of the preop value in 10 minutes)

  Missing gland – check inferiorly in thymus tissue (most common ectopic location, can remove tail of the thymus and see if PTH drops), near carotids, vertebral body, superior to pharynx, thyroid

  Still cannot find gland – close and follow PTH; if PTH still ↑, get sestamibi scan to localize

  At reoperation for a missing gland, the most common location for the gland is normal anatomic position

  Hypocalcemia postop – from bone hunger or failure of parathyroid remnant/graft

•  Bone hunger – normal PTH, decreased HCO₃⁻

•  Aparathyroidism – decreased PTH, normal HCO₃⁻

  Persistent hyperparathyroidism (1%) – most commonly due to missed adenoma remaining in the neck

  Recurrent hyperparathyroidism – occurs after a period of hypocalcemia or normocalcemia

•  Can be due to new adenoma formation

•  Can be due to tumor implants at the original operation that have now grown

•  Need to consider recurrent parathyroid CA

  Reoperation associated with ↑ risk of RLN injury, permanent hypoparathyroidism

  Sestamibi scan

•  Will have preferential uptake by the overactive parathyroid gland

•  Good for picking up adenomas but not 4-gland hyperplasia

•  Best for trying to pick up ectopic glands

SECONDARY HYPERPARATHYROIDISM

  Seen in patients with renal failure

  ↑ PTH in response to low Ca

  Most do not need surgery (95%)

  Ectopic calcification and osteoporosis can occur

  Tx: Ca supplement, vitamin D, control diet PO₄, PO₄-binding gel, ↓ aluminum

•  Surgery for bone pain (most common indication), fractures, or pruritus (80% get relief)

•  Surgery involves total parathyroidectomy with autotransplantation or subtotal parathyroidectomy

TERTIARY HYPERPARATHYROIDISM

  Renal disease now corrected with transplant but still overproduces PTH

  Has similar lab values as primary hyperparathyroidism (hyperplasia)

  Tx: subtotal (3½ glands) or total parathyroidectomy with autoimplantation

FAMILIAL HYPERCALCEMIC HYPOCALCIURIA

  Patients have ↑ serum Ca and ↓ urine Ca (should be ↑ if hyperparathyroidism)

  Caused by defect in PTH receptor in distal convoluted tubule of the kidney that causes ↑ resorption of Ca

  Dx: Ca 9–11, have normal PTH (30–60), ↓ urine Ca

  Tx: nothing (Ca generally not that high in these patients); no parathyroidectomy

PSEUDOHYPOPARATHYROIDISM

  Because of defect in PTH receptor in the kidney, does not respond to PTH

PARATHYROID CANCER

  Rare cause of hypercalcemia

  ↑ Ca, PTH, and alkaline phosphatase (can have extremely high Ca levels)

  Lung most common location for metastases

  Tx: wide en bloc excision (parathyroidectomy and ipsilateral thyroidectomy)

  50% 5-year survival rate

  Mortality is due to hypercalcemia

  Recurrence in 50%

MULTIPLE ENDOCRINE NEOPLASIA SYNDROMES

  Derived from APUD cells

  Neoplasms can develop synchronously or metachronously

  Autosomal dominant, 100% penetrance

  MEN I

•  Parathyroid hyperplasia

•  Usually the 1st part to become symptomatic; urinary symptoms

•  Tx: 4-gland resection with autotransplantation

•  Pancreatic islet cell tumors

•  Gastrinoma #1 – 50% multiple, 50% malignant; major morbidity of syndrome

•  Pituitary adenoma

•  Prolactinoma #1

•  Need to correct hyperparathyroidism 1st if simultaneous tumors

  MEN IIa

•  Parathyroid hyperplasia

•  Medullary CA of thyroid

•  Nearly all patients; diarrhea most common symptom; often bilateral

•  #1 cause of death in these patients

•  Usually 1st part to be symptomatic

•  Pheochromocytoma

•  Often bilateral, nearly always benign

•  Need to correct pheochromocytoma 1st if simultaneous tumors

  MEN IIb

•  Medullary CA of thyroid

•  Nearly all patients; diarrhea most common symptoms; often bilateral

•  #1 cause of death in these patients

•  Usually 1st part to be symptomatic

•  Pheochromocytoma

•  Often bilateral, nearly always benign

•  Mucosal neuromas

•  Marfan’s habitus, musculoskeletal abnormalities

•  Need to correct pheochromocytoma 1st if simultaneous tumors

  MEN I – MENIN gene

  MEN IIa and IIb – RET proto-oncogene

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