DR BURNS: Ms
Q is a 64-year-old woman with a history of mild hypercalcemia and hyperparathyroidism.
She has managed care insurance.
Ms Q states that on a routine blood test 7 years ago she was noted to
have a calcium level of 10.1 mg/dL (2.5 mmol/L). She has subsequently had
her calcium checked on a biannual basis and it has ranged from 10.4 to 11.3
mg/dL (2.6-2.8 mmol/L). Ms Q was referred to an endocrinologist in December
2002 after her calcium was higher than 11 mg/dL (2.7 mmol/L) on 3 occasions.
Her laboratory studies just prior to her visit revealed a calcium level of
11.1 mg/dL (2.8 mmol/L), a parathyroid hormone (PTH) level of 102 pg/mL, and
a phosphate level of 3.4 mg/dL.
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A, The normal feedback relationship between calcium and parathyroid
hormone is shown. Parathyroid hormone is suppressed by calcium over the normal
range for serum calcium (shaded area), with the set point for calcium at the
midpoint of the curve. In all forms of hyperparathyroidism the adenoma is
relatively insensitive to feedback suppression by calcium. This results in
a shift to the right in the feedback relationship and an increase in the set
point for serum calcium. B, An increase in the set point for serum calcium
is a determinant of parathyroid adenoma growth. The adenoma size increases
until it reaches a sufficient size to maintain parathyroid hormone and serum
calcium at the new set point, and the adenoma then stops growing.
A, In the early phase, sestamibi is taken up by thyroid tissue (black
arrowheads) and parathyroid (yellow arrowhead). B, Parathyroid uptake persists
at a later time (yellow arrowhead).
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