Serum melatonin levels: a new neurodiagnostic tool in pineal region tumors?

The pineal hormone melatonin (MLT) is secreted in a circadian rhythm with high serum levels during nighttime and low serum levels during daytime. Several authors have reported an altered secretion pattern of MLT in patients with pineal tumors and have proposed that MLT may be used as a tumor marker. In nine patients, a pineal region tumor was diagnosed by computer-assisted tomography. Before and after surgical removal of the tumor, several day- and nighttime serum samples were collected and MLT concentrations were estimated by radioimmunoassay. Before operation, five patients presented a normal circadian pattern of MLT secretion. In the remaining four subjects, MLT levels were undetectable or at the limit of detection, with no signs of a circadian secretion pattern. Eight patients were reexamined after tumor resection, when all but one had undetectable or very low MLT levels. The remaining subject, with a pineomesencephalic pilocytic astrocytoma, dislocating but not involving the pineal gland, presented a normal circadian secretion pattern of MLT after operation; in this case, tumor resection was possible without damaging the pineal gland. Thus, before operation, MLT deficiency rather than exaggerated serum levels may be used as a marker for pineal tumors that destroy the pineal gland. After tumor resection, serum MLT may serve to demonstrate complete pinealectomy.