SERUM PROLACTIN CONCENTRATIONS ARE ELEVATED AFTER SYNCOPE

The distinction between syncope and epileptic seizures is a common cli nical diagnostic problem. Elevated serum prolactin (PRL) concentration s are used to help differentiate epileptic from nonepileptic attacks s uch as pseudoseizures. Reports of PRL concentrations following syncope have been variable. To determine whether PRL rises after syncope, we measured serum PRL concentrations during a 45-minute passive 60-degree head-up tilt in 21 patients with a history of near-fainting or syncop e. Head-up tilt triggered hypotension (mean arterial pressure 51 mm Hg , 95% CI = 45-57) with syncope in 11 patients. PRL concentrations were elevated (>19 ng/mL) and reached a maximum within the first 30 minute s after tilt-induced syncope in nine patients (PRL supine: 11 ng/mL, 9 5% CI = 7-15, vs. PRL after syncope: 52 ng/mL, 95% CI = 36-67; a great er than fourfold rise), while they remained unchanged in 10 patients w ho had a normal response to head-up tilt (PRL supine: 6 ng/mL, 95% CI = 5-8, vs. maximum PRL while upright: 8 ng/mL, 95% CI = 6-10). The fin dings indicate that elevated PRL concentrations are present after hypo tensive syncope and are of little use in differentiating such syncope from epileptic seizures.