In primarily or secondarily generalized tonic-clonic seizures and partial complex seizures of temporal lobe origin, the serum prolactin level rises at least threefold, and often more (fivefold to twentyfold).90 This transient postictal elevation has been used clinically to distinguish these seizures from nonepileptic seizures. Prolactin levels, unlike cortisol levels,91 are seldom elevated in nonepileptic seizures. Rises that do occur are limited to the twofold level that can accompany stress or occur postprandially.

Thus a postictal prolactin elevation greater than threefold suggests the presence of epileptic seizure. The lack of such an elevation makes it unlikely that an ictal event was epileptic if the event was a tonic-clonic seizure.

There are several limitations on the usefulness of postictal serum prolactin elevation as a test to distinguish epileptic from nonepileptic seizures:

• Postictal serum prolactin elevation cannot be used to differentiate simple partial seizures or absence seizures from nonepileptic seizures.
• Prolactin levels may increase during syncope, demonstrated during tilt table studies.92
• Complex partial seizures that do not arise from the temporal lobe do not lead to prolactin elevation.
• 10% to 20% of patients with tonic-clonic seizures may not show a postictal prolactin rise.
• Ambiguous test results, such as a twofold elevation, are difficult to interpret.
• Prolactin level rises predictably only after a single seizure. Patients who have more than 2 seizures in 12 hours have progressively smaller elevations, presumably because stored prolactin from the pituitary lactotrophs is exhausted.

With these caveats, however, the test is a useful one. One simple protocol involves checking serum prolactin level 20 minutes and 12 hours postictally (24 hours in outpatient settings) in patients whose seizure frequency is less than 1 in 12 hours. The value measured 12 or 24 hours after the seizure serves as the patient's own post-hoc baseline.

Adapted from: Klein P and Herzog AG. Endocrine aspects of partial seizures. In: Schachter SC, Schomer DL, eds. The comprehensive evaluation and treatment of epilepsy. San Diego, CA: Academic Press; 1997. p. 207-232.
With permission from Elsevier (www.elsevier.com).
Reviewed and revised May 2004 by Cynthia Harden, MD, Weill Cornell Medical College.