The measurement of serum prolactin is a useful blood test in diagnosing seizure disorders. Prolactin is a polypeptide hormone produced by the anterior pituitary, involved in milk production and endocrine function. Unlike most pituitary hormones, prolactin is under negative hypothalamic control via prolactin inhibiting factor. When seizure activity influences the hypothalamic-pitu-itary axis, prolactin inhibiting factor is presumed to be inhibited itself, and prolactin is released into the circulation. Trimble (105) first showed that serum prolactin rises with generalized epileptic seizures, but not with psy-chogenic seizure-like episodes. Complex partial seizures can also raise serum prolactin. Sensitivity is approximately 90% for tonic-clonic seizures and 70% for complex partial seizures (106). Complex partial seizures originating in the frontal lobes rarely elevate serum pro-lactin (89,90), again emphasizing the difficulty in diagnosis of frontal lobe epilepsy. Several conditions can generate false-positive elevations of serum prolactin (see Chapter 5), including: stress, surgery, general anesthesia, strenuous exercise, sleep, orgasm, breast stimulation, estrogens, endometriosis, primary hypothyroidism, pro-lactin secreting pituitary adenomas, multiple sclerosis, phenothiazines and butyrophenones, opiates, L-DOPA, bromocriptine, other ergots, apomorphine, metoclopro-mide, and some antiepileptic drugs. Therefore, acute rises of two to three times the baseline levels are more specific for the diagnosis of a seizure than is an elevated single serum level (106).
Serum prolactin elevations reach a peak 10 to 20 minutes after a seizure and return to baseline by 60 minutes after a seizure (107). This imposes a practical limit on the use of prolactin to diagnose epilepsy, because most spells occur away from a medical setting. We have shown that prolactin accurately can be assayed by pricking the finger and applying capillary blood to filter paper (108). The specimen is stable at room temperature for a week and may be analyzed at leisure. This finding opens the possibility of using a suitable kit in the home or work setting to determine if infrequently recurrent spells are seizures. One remaining limitation of prolactin for diagnosis is a lack of available data on prolactin levels after several of the imitators of epilepsy, including cerebrovascular ischemia or migraine.
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