Giant pituitary prolactinoma with falsely low serum prolactin: the pitfall of the "high-dose hook effect": case report.
OBJECTIVE AND IMPORTANCE: We present a case of a giant prolactinoma with a falsely low serum prolactin concentration determined by a two-site chemiluminometric assay. Awareness of the possibility of the "high-dose hook effect" in such cases will prevent preoperative misdiagnosis. CLINICAL PRESENTATION: A patient with a giant invasive pituitary tumor was found preoperatively to have serum prolactin of 31 ng/ml. Pathological examination of the excised tissue, however, demonstrated strong staining for prolactin. INTERVENTION: Serial dilutions of the serum disclosed hyperprolactinemia of 280,000 ng/ml, establishing the presence of the "high-dose hook effect." Treatment with pergolide (Permax; Athena Neurosciences, S. San Francisco, CA) decreased tumor size and lowered serum prolactin by more than 99%. CONCLUSION: A "high-dose hook effect" needs to be suspected in every patient with a giant pituitary adenoma (>3 cm) and normal serum prolactin. Subsequently assaying the diluted serum will reliably disclose this phenomenon and allow correct diagnosis and therapy.[1]References
- Giant pituitary prolactinoma with falsely low serum prolactin: the pitfall of the "high-dose hook effect": case report. Barkan, A.L., Chandler, W.F. Neurosurgery (1998) [Pubmed]
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