Primary Hyperparathyroidism

• Incidence:
  • The incidence of PHPT has remained relatively stable in the last couple of decades
  • PHPT is more common in women than in men:
    • Two to three times higher in incidence rate in women
  • PHPT is more common in the elderly population:
    • The incidence increases with age
    • The incidence starts to increase at age 50:
      • 1 in 500 postmenopausal women will have PHPT
      • 1 in 1000 men over 50 will have PHPT
  • Incidence rates in the USA:
    • 60 cases per 100, 000 women
    • 20 cases per 100,000 men
• Prevalence
  • In the USA:
    • 1% of the postmenopausal female population will have PHPT
  • International prevalence rates:
    • 3% of the postmenopausal female population will have PHPT
  • The prevalence PHPT has risen in the last couple of decades:
    • From 1995 and 2010 it has tripled:
      • Women:
        • 76 to 233 cases per 100,000 women
      • Men:
        • 30 to 85 cases per 100,000 men
  • Gender:
    • African Americans have the highest prevalence of PHPT:
      • Followed by caucasians followed by Asians
    • Hispanics have a lower prevalence rate
  • Reason for the higher prevalence compared to incidence in PHPT:
    • Is that only 20% to 25% of patients with PHPT in the USA will end up having surgery
    • Only 50% of patients in the USA with nephrolithiasis and PHPT have surgery
    • Only 20% of patients with osteoporosis and PHPT in the USA go onto have surgery
    • The probability of having surgery decreases with age:
      • The older one gets the less likely they will be offered an intervention
• Genetics of PHPT:
  • Six primary conditions associated with an inherited predisposition for the development of PHPT:
    • MEN Type 1:
      • Incidence:
  • The incidence of PHPT has remained relatively stable in the last couple of decades
  • PHPT is more common in women than in men:
    • Two to three times higher in incidence rate in women
  • PHPT is more common in the elderly population:
    • The incidence increases with age
    • The incidence starts to increase at age 50:
      • 1 in 500 postmenopausal women will have PHPT
      • 1 in 1000 men over 50 will have PHPT
  • Incidence rates in the USA:
    • 60 cases per 100, 000 women
    • 20 cases per 100,000 men
• Prevalence
  • In the USA:
    • 1% of the postmenopausal female population will have PHPT
  • International prevalence rates:
    • 3% of the postmenopausal female population will have PHPT
  • The prevalence PHPT has risen in the last couple of decades:
    • From 1995 and 2010 it has tripled:
      • Women:
        • 76 to 233 cases per 100,000 women
      • Men:
        • 30 to 85 cases per 100,000 men
  • Gender:
    • African Americans have the highest prevalence of PHPT:
      • Followed by caucasians followed by Asians
    • Hispanics have a lower prevalence rate
  • Reason for the higher prevalence compared to incidence in PHPT:
    • Is that only 20% to 25% of patients with PHPT in the USA will end up having surgery
    • Only 50% of patients in the USA with nephrolithiasis and PHPT have surgery
    • Only 20% of patients with osteoporosis and PHPT in the USA go onto have surgery
    • The probability of having surgery decreases with age:
      • The older one gets the less likely they will be offered an intervention
• Genetics of PHPT:
  • Only 5% to 10% of patients with PHPT will with have an underlying genetic predisposition
  • Six primary conditions associated with an inherited predisposition for the development of PHPT:
    • MEN Type 1:
      • Pituitary Tumors
      • PHPT:
        • Has almost 100% penetrance
        • It is the first endocrine disease to manifest
        • It manifests at a young age
      • Pancreatic neuroendocrine tumors:
        • Duodenal and gastronomes
      • Foregut carcinoid tumors:
        • Lung
        • Thymus
      • Adrenal adenomas
    • MEN Type 2A:
      • Medullary thyroid carcinoma:
        • 100% penetrance
        • First endocrinopathy to manifest
      • Pheochromocytoma
      • PHPT:
        • Only 20% to 30% develop PHPT
        • Will depend on the RET mutation (codon)
        • They develop mild hypercalcemia
        • More common to see multi gland disease but you can also get one gland disease
        • Age of onset is younger:
          • Two decades earlier than sporadic PTHP
    • MEN Type IV:
      • Phenotypically similar to MEN type 1
      • Mutation CDKNIB gene
    • Hyperparathyroidism jaw tumor syndrome (rare):
      • Ossifying fibromas
      • Mixture of renal tumors, uterine fibroids
    • Familial hypocalciuric hypercalcemia (FHH – predisposes to hypercalcemia):
      • FHH is mainly classified into three different types depending on the genetic cause
      • FHH type 1:
        • Is the most common type of FHH and is caused by changes (also known as pathogenic variants or mutations) in the CASR gene
        • The protein made from the CaSR gene:
          • The calcium-sensing receptor (CaSR protein), monitors and regulates the level of calcium in the blood
      • FHH type 2:
        • Is caused by changes in the GNA11 gene
      • FHH type 3:
        • Is caused by changes in the AP2S1 gene
      • All three types of FHH are inherited in:
        • An autosomal dominant manner
      • In rare cases, FHH may be caused when a person’s immune system mistakenly makes antibodies that attack the CaSR protein:
        • The autoimmune form of FHH is not known to be caused by changes in a specific gene
      • Diagnosis of FHH:
        • Is suspected by high levels of calcium in the blood:
          • Especially when there are no other symptoms present
        • Further blood and urine tests may be used to rule out other possible causes
        • Genetic testing can confirm the diagnosis of FHH, except in rare autoimmune cases
      • Treatment:
        • Is typically considered unnecessary because most people with FHH do not have symptoms
        • If pancreatitis occurs, removal of the parathyroid gland may be recommended
    • Isolated familial PHPT
• Management of inherited PHPT:
  • In many cases PHPT is the first manifestation of a hereditary syndromic disease:
    • Goal of surgery is to normalize PTH and provide best chances for long term disease free outcome
  • Pitfalls in imaging in patients with MEN type 1:
    • Present with parathyroid gland asymmetry:
      • Most of this cases are secondary to hyperplasia not adenoma
  • The gold standard for the management of MEN type 1 is:
    • Bilateral neck exploration with a subtotal parathyroidectomy or total parathyoidectomy with autotransplantation (to the sternocleidomastoid muscle of the neck or the brachioradialis muscle of the forearm):
      • Biochemical cure are very similar between both approaches
      • With autotransplantation there is a 3% to 10% risk that the autotransplanted gland does not take leading to hypoparathyroidism:
        • For this reason cryopreservation might be a good option (they can be kept in this state for up to 2 years)
    • Remember that 3% to 5% of the cases of MEN type 1 might have super numerary glands:
      • This glands might hide in the thymus / thryothymic ligament or other ectopic locations
  • Intraoperative PTH measuring:
    • Allows us to decide how much of a gland remnant can be left behind to achieve longterm cure:
      • Achieving a intact PTH less that 40 pg/dl supports a longer long term free of recurrence
    • If the intraoperative PTH is very low it can helps us decide to autotransplant a gland to decrease that incidence of postoperative permanent hypoparathyroidism
  • Management of MEN type IIa:
    • All of this patients will have manifested with medullary thyroid cancer (MTC) or will be diagnosed with MTC and PHPT at the same time
    • The operative report of the thyroid cancer case is required along with the pathology report:
      • Talking with the surgeon that performed the thyroidectomy will be beneficial
    • At least two localizing studies that are concordant
    • Use cryopreservation in re due cases:
      • Because we might not have the information of how many glands were removed or injured during the thyroid surgery
    • Autotransplantation might be a good option when managing PHPT because MTC commonly recurs in the neck
    • If operating for the MTC and PHPT at the same time:
      • The surgery for PHPT remove the abnormal gland check intraoperative PTH (make sure it is normal) and leave the rest of the normal glands in situ
    • If subtotal thyroidectomy is performed:
      • Leave a portion of a gland that is about the same size as a normal gland
      • Make sure it is well vascularized
      • If possible leave an inferior gland:
        • They are easier to localize than a superior gland in re due cases
        • Prevents deep dissection close to the RLN in re due cases

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