Abstract #1165468: Stalk Effect: Cushing’s Disease Mistaken for Prolactinoma

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The diagnostic workup for hypercortisolism is not infrequent in clinical practice. Common findings of high cortisol are weight gain, facial plethora, and menstrual irregularity. Here we discuss a distinct presentation of amenorrhea and galactorrhea as an unexpected exhibition of Cushing’s disease. A 35-year-old woman with a history of obesity presented with the chief complaint of infertility. Six months prior, she began to experience amenorrhea, galactorrhea, headaches, excessive sweating, and weight gain. Serum prolactin (PRL) level was found to be mildly elevated at 35.3 ng/mL. Magnetic resonance imaging (MRI) of the brain demonstrated a 11 mm x 9.8 mm x 9.6 mm pituitary macroadenoma. She was started on oral cabergoline 0.5 milligrams twice weekly for prolactinoma treatment, with resolution of all symptoms and return to normal PRL range. Tumor size on repeat MRI was stable. Six months later, she conceived. Cabergoline was stopped. She delivered a healthy infant but developed recurrence of her symptoms, now with diplopia. PRL was elevated at 61.9 ng/mL. Cabergoline was reinitiated. Further labs demonstrated elevated plasma adrenocorticotropic hormone (ACTH) of 121 pg/ml, elevated morning salivary cortisol of 0.217 ug/dL and elevated urinary free cortisol of 142 ug/24 hour. Overnight dexamethasone test showed unsuppressed cortisol. Cushing’s disease was diagnosed. Tumor size was 13 mm x 17 mm x 17 mm prior to surgical resection. Tumor pathology showed corticotroph adenoma. PRL highlighted in just a few scattered tumor cells. Her elevated prolactin levels were ultimately suspected to be due to stalk effect. Approximately 40% of all pituitary adenomas are prolactinomas. Clinical signs and symptoms of hyperprolactinemia include infertility, amenorrhea, and galactorrhea. Mild elevations of prolactin may cause infertility and can be consistent with prolactinoma. Amenorrhea associated with galactorrhea strongly suggests hyperprolactinemia. However, clinicians must note that in the presence of sellar mass and mild hyperprolactinemia, a non-prolactin-secreting mass must first be diagnostically ruled out. Cushing’s disease may present similarly with menstrual irregularities, hyperprolactinemia, and galactorrhea due to stalk effect. This patient demonstrated initial diagnostic uncertainty due to her incomplete workup and rapid clinical response to cabergoline. Her elevations in prolactin and response to cabergoline at the time of her original presentation may substantiate the proposed off-label use of dopamine agonists in non-prolactinoma pituitary tumors.