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CASE FILES: BIOCHEMISTRY
A N SW E R S TO C A SE 51: H Y PE R PA R A T H Y R O ID ISM
Summary:
A 42-year-old female, who has a history of frequent urinary tract
infections and kidney stones, is found to have vague abdominal pain and
weakness, with hypercalcemia and decreased phosphorus levels.
Diagnosis: Hyperparathyroidism, leading to hypercalcemia and
hyperphosphatemia.
Biochemical mechanism: Elevated parathyroid hormone level acts by
binding its 7-helix plasma membrane receptor to activate the adenylate
cyclase/protein kinase A signaling system.
C L IN IC A L C O R R E L A T IO N
This patient presents with kidney stones, which causes severe flank pain.
The most common causes of hypercalcemia include malignancies or
hyperparathyroidism. Other causes include granulomatous disorders such as
sarcoid and tuberculosis, and less commonly, hypercalcemia may be the pres-
entation of intoxication with vitamins A or D, or calcium-containing antacids,
or occur as a side effect of drug therapies like lithium or thiazide diuretics.
Genetic conditions like familial hypocalciuric hypercalcemia and hyper-
parathyroidism as part of a multiple endocrine neoplasia syndrome are also
uncommon. Primary hyperparathyroidism, usually because of a solitary
parathyroid adenoma, is the most likely cause when hypercalcemia is dis-
covered in an otherwise asymptomatic patient on routine laboratory screening.
Most patients have no symptoms with mild hypercalcemia below 12.0 mg/dL,
except perhaps some polyuria and dehydration. With levels above 13 mg/dL,
patients begin developing increasingly severe symptoms. These include central
nervous system (CNS) symptoms (lethargy, stupor, coma, mental status changes,
psychosis), gastrointestinal symptoms (anorexia, nausea, constipation, peptic
ulcer disease), kidney problems (polyuria, nephrolithiasis), and musculoskele-
tal complaints (arthralgias, myalgias, weakness.) The symptoms of hyper-
parathyroidism can be remembered as: stones (kidney), moans (abdominal
pain), groans (myalgias), bones (bone pain), and psychiatric overtones.
Diagnosis can be established by finding hypercalcemia and hypophosphatemia,
with inappropriately elevated PTH levels. Symptomatic patients can be treated
with parathyroidectomy.
A PPR O A C H TO C A L C IU M M E T A B O L ISM
O bjectives
1.
Be familiar with calcium metabolism.
2.
Know about regulation of serum calcium including the roles of
parathyroid hormone and calcitonin.
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