Endocrine Abstracts

Introduction: Prolactinomas are the most common hormonally active pituitary tumors that account for 40–60% of all pituitary adenomas and are usually successfully treated with dopamine agonists. Surgery or radiotherapy is reserved for drug intolerance/resistance or in neuro-ophthalmological emergencies. We present a patient with refractory microprolactinoma with empty sella treated by transsphenoidal surgery.

Case: 42-year-old female patient admitted with a 14 years history of prolactinoma being treated with dopamine agonists for ten years. At the end of the tenth year, the tumor was resistant to high dose cabergoline (4 mg/week). Magnetic resonance imaging (MRI) revealed a partial empty sella with 6.5×3.5 mm pituitary adenoma. She underwent transsphenoidal surgery. Histopathologically, a pituitary adenoma with rare mitotic figures, Ki-67 index of 2%, no expression of p53 and no other features of atypia was identified. Immunohistochemistry showed expression of prolactin by majority of the cells. Postoperative MRI demonstrated empty sella (height of the gland was 2 mm) and no residual mass. After operation, cabergoline was restarted because of high prolactin levels and amenorrhea. Despite a substantial increase in dosage there was no clinical improvement in amenorrhea and galactorrhea and there was not any biochemical response. Her other anterior pituitary hormones were normal while serum prolactin was 255 ng/ml (4.79–25.3 ng/ml) in her last visit.

Conclusion: A minority of patients, ranging from 10–20% in different series does not achieve normoprolactinemia and/or tumor shrinkage despite treatment with high doses of dopamine agonists. Those tumors are usually macroadenomas with cavernous sinus invasion and rarely microadenomas. Resistance can be documented by demonstrating the absence or poor expression of D2 receptors on the membrane surface of tumor cells, or abnormalities at a postreceptor level. However, molecular biology studies cannot be routinely performed in our center. Exchange of cabergoline with bromocriptine was successful in few cases in the literature.