Pituitary apoplexy
C. Order urgent computed tomography scan and computed tomography angiography of the brain
The differential diagnosis for sudden onset of headache, nausea, and binocular vertical diplopia in a young patient is limited. The presence of left infraduction limitation and corresponding left hypertropia that does not fit the pattern for fourth nerve palsy could be because of partial third cranial nerve palsy. The relevant medical history of hyperprolactinemia makes pituitary apoplexy (ie, sudden hemorrhage within the pituitary gland, often within preexisting pituitary adenoma) and aneurysmal compression of the third nerve the most critical diagnoses to be ruled out. Thus, ordering an urgent computed tomography scan and computed tomography angiography scan of the brain with attention to the sellar region (choice C) would be the most appropriate course of action. Checking thyrotropin and thyroid autoantibody levels and ordering orbital imaging (choice A) would be correct if thyroid eye disease was the suspected culprit. However, sudden onset of headache and nausea is not a typical presentation of thyroid eye disease, making this diagnosis unlikely. While myasthenia gravis can present with vertical binocular diplopia, it would also not explain the sudden onset of headaches and nausea, and other likely signs of myasthenia gravis (eg, orbicularis oculi weakness and variable ptosis fatigable in sustained upgaze) were not present. Thus, ordering acetylcholine receptor antibody level titers (choice B) would not be the most important investigation. Lumbar puncture (choice D) would be the best test to order if subarachnoid hemorrhage were suspected as causing sudden onset of headache and nausea. However, computed tomography scan and computed tomography angiogram imaging are sensitive for identifying aneurysms and detecting blood in the subarachnoid space; thus it should be performed first.