October 04, 2010

PLAB Question 4

A 28-year-old woman sought medical attention for amenorrhea of two years' duration. Normal menarche had occurred at age 13, followed by regular menstrual cycles. At age 25, she had noticed a diminution in the frequency of menses, and at age 26, menses had ceased. Around that time she also had noticed a milky discharge from both breasts. A visual field test reveals bitemporal hemianopsia. Family history is unremarkable.

The investigation of choice at this stage would be

a) skull x-ray
b) non-contrast CT scan brain
c) contrast CT scan brain
d) contrast enhanced MRI of the optic nerves
e) four vessel cerebral angiogram
f) single vessel cerebral angiogram
g) MR cerebral Angiography
h) mri with emphasis on the frontal lobe
i) mri of the pituitary gland
j) mri with emphasis on the temporal lobe

The correct answer is I

The most important positive finding in the history is the development of milky discharge from the breasts, concurrent with secondary amenorrhea. On the basis of the history, one can make a presumptive diagnosis of amenorrhea and galactorrhea from hyperprolactinemia.

Causes of hyperprolactinemia that must be considered include a prolactin-secreting pituitary tumor (although the negative family history reduces the likelihood of MEN type I); a functional disorder in the hypothalamus that has blocked the release of dopamine, which inhibits the pituitary's production of prolactin; and rare disorders such as ectopic production of prolactin by a tumor (e.g., lung or kidney carcinoma). Primary hypothyroidism is another consideration, since it is also a cause of hyperprolactinemia.

Skull films and CT-scans have been replaced by MRI for imaging of the pituitary fossa and sella turcica. These may still be used in centers without an MRI.

The results of the eye examination in this patient are very important because a pituitary macroadenoma--that is, an adenoma larger than 1 cm--that extends above the level of the sella turcica may impinge on the optic chiasm and cause a bitemporal hemianopsia or impinge on the optic nerves and cause blind spots. Upward enlargement can involve hypothalamic tissue and the brain stem, as well as the optic chiasm. The classic finding of chiasmatic involvement is bitemporal hemianopsia.

An additional finding of a junctional scotoma (a central scotoma in one eye with reduced visual acuity and an upper temporal field defect in the opposite eye) combines with bitemporal hemianopsia to account for up to 96% of all visual defects.

Hypothalamic damage can result in hypotension, disturbed thermoregulation, and cardiac dysrhythmias. Brain stem compression causing altered levels of consciousness and changes in muscle tone, respiratory and pupillary reactions, and unusual signs such as hiccoughs and retraction nystagmus.

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