Delayed visual loss following pergolide treatment of a prolactinoma

A patient who had achieved marked improvement in vision and shrinkage of a prolactinoma following treatment with pergolide (0.1 mg/day) suffered a marked worsening of vision 7 months after continued treatment at the same dose. Brain magnetic resonance imaging (MRI) at the time of visual loss showed further shrinkage of the tumor and prolapse of the chiasm into the pituitary fossa. The dose of pergolide was cut in half (0.05 mg/day); 12 months later, vision had completely recovered. Brain MRI at the time of visual recovery showed no change in the position of the prolapsed chiasm. This is the 11th reported case of delayed visual loss following dopaminergic treatment of prolactinoma. Recovery of vision always occurs with reduction of the medication dosage. Many patients whose prolactinomas are treated in this fashion display chiasmal prolapse, and few suffer visual loss. Considering that visual recovery occurs without a visible change in the position of the chiasm, traction is an unlikely cause of delayed visual loss. Therefore, the term chiasmal traction syndrome, used to describe visual loss with prolapsed chiasm following surgical and radiation treatment of sellar tumors, should not be applied in this setting lest it prompt consideration of surgical chiasmapexy. The proper management is reduction of the dopaminergic agonist dosage.