What is the next step in evaluating a 45-year-old female with a history of Gastroesophageal Reflux Disease (GERD), anxiety/depression, migraine headaches, and cyclic vomiting, who presents with increased episodes of dizziness, headache, and vomiting, and has hyperprolactinemia and hyperparathyroidism?

Recommended Next Step in Work-Up

Order a pituitary MRI to evaluate for a prolactinoma, as the prolactin level of 50 ng/mL strongly suggests a pituitary adenoma, particularly given the constellation of symptoms including headache, dizziness, and cyclic vomiting. 1

Rationale for Pituitary MRI

The prolactin elevation to 50 ng/mL is the most critical finding requiring immediate investigation. According to the Endocrine Society, prolactin levels around 50 ng/mL typically indicate either a microprolactinoma or small macroadenoma, making MRI the appropriate next diagnostic step. 1 The degree of prolactin elevation correlates directly with tumor size, and this level is well above the threshold for mild elevation (>17 ng/mL). 1

Before ordering the MRI, you must first exclude secondary causes of hyperprolactinemia:

• Check TSH immediately - Primary hypothyroidism causes hyperprolactinemia in 40-43% of cases and must be ruled out first 1
• Review all medications - Dopamine antagonists (including antiemetics like metoclopramide or prochlorperazine) are among the most common causes of drug-induced hyperprolactinemia 1
• Assess for macroprolactin - This accounts for 10-40% of hyperprolactinemia cases and represents biologically inactive prolactin complexes with low clinical significance 1

Critical Diagnostic Considerations

The patient's symptom complex of cyclic vomiting, migraine headaches, and anxiety/depression is highly consistent with cyclic vomiting syndrome (CVS), which has strong associations with both migraine and mood disorders. 2, 3 However, the hyperprolactinemia raises concern for a pituitary adenoma that could be contributing to or causing these symptoms through:

• Mass effect - Headaches and dizziness could represent compression effects 2
• Hormonal disruption - Hyperprolactinemia itself can cause headaches and nausea 1
• Hypothalamic-pituitary axis dysfunction - This can manifest with various neurological and autonomic symptoms 2

Important Caveats

Watch for the "hook effect" - If MRI reveals a large pituitary mass but prolactin seems disproportionately low for tumor size, request serial dilutions of the serum sample. This phenomenon occurs in approximately 5% of macroprolactinomas where extremely high prolactin concentrations saturate the immunoassay, producing falsely low measurements. 1

If macroadenoma is found, visual field testing is mandatory due to risk of optic chiasm compression. 1

Addressing the PTH Elevation

The PTH of 62 pg/mL (assuming upper limit of normal ~65 pg/mL) represents mild elevation. While this could indicate primary hyperparathyroidism, it is less urgent than the prolactinoma workup. After addressing the pituitary pathology:

• Check serum calcium, phosphorus, and vitamin D levels
• If calcium is elevated with elevated PTH, this confirms primary hyperparathyroidism
• If calcium is normal, consider secondary hyperparathyroidism from vitamin D deficiency or renal insufficiency

Management of Cyclic Vomiting Syndrome

While pursuing the prolactinoma workup, the patient's CVS requires concurrent management. Screen for cannabis use immediately - use >4 times weekly for >1 year suggests cannabinoid hyperemesis syndrome rather than CVS. 3, 4

For acute episodes, provide:

• Sumatriptan 20 mg intranasal at prodrome onset (recognize symptoms: impending doom, anxiety, diaphoresis, mental fog) 3
• Ondansetron 8 mg sublingual every 4-6 hours 3

If episodes are moderate-severe (≥4 episodes/year lasting >2 days), initiate prophylaxis with amitriptyline 25 mg at bedtime, titrating to 75-150 mg nightly, with baseline ECG monitoring for QTc prolongation. 2, 3 This medication has the added benefit of treating comorbid anxiety/depression and migraine prophylaxis. 5

Common Pitfalls to Avoid

• Do not assume the hyperprolactinemia is stress-related without excluding structural and secondary causes 1
• Do not start dopamine agonist therapy for mild, asymptomatic hyperprolactinemia before completing the diagnostic workup 1
• Do not overlook medication-induced causes - antidepressants used for anxiety/depression can worsen GERD through anticholinergic effects on the lower esophageal sphincter 6
• Do not miss the prodromal window for CVS abortive therapy - effectiveness drops dramatically if medications aren't taken at symptom onset 3