No abstract

To investigate whether activation of afferent and central baroreceptor pathways could differentiate between pure autonomic failure (PAF) and multiple system atrophy with autonomic failure (MSA), we determined the effect of upright tilt on circulating levels of vasopressin in patients with PAF and patients with MSA. We also studied 14 normal subjects, nine of whom developed acute hypotension due to vasovagal syncope. In patients with PAF and in normal subjects with vasovagal syncope, upright tilt induced marked hypotension and a pronounced increase in the plasma concentration of vasopressin (1.1 +/- 0.3 to 38.0 +/- 8.0 pmol/l in PAF and 1.0 +/- 0.2 to 27.4 +/- 7.2 pmol/l in vasovagal syncope, p less than 0.005 for both). In patients with MSA, upright tilt also elicited profound hypotension but circulating levels of vasopressin increased little (0.5 +/- 0.1 to 1.5 +/- 0.3 pmol/l, p less than 0.05). During upright tilt, the plasma concentration of norepinephrine significantly increased in normal subjects but did not increase in patients with autonomic failure. Our results indicate that afferent and central baroreceptor pathways involved in vasopressin release are normal in patients with PAF but are impaired in patients with MSA. Thus, measurement of baroreceptor-mediated vasopressin release appears to provide a clear marker to differentiate between patients with PAF and patients with MSA.

S ince the initial paper by Trimble in 1978 1 highlighting postictal levels of serum prolactin as a way to separate epileptic from nonepileptic seizures, PubMed has logged approximately 300 articles retrievable by the search terms "epilepsy" and "prolactin." Despite this considerable body of work, the role of serum prolactin in diagnosis of seizures remains uncertain. In this issue of Neurology ® Clinical Practice, Abubakr and Wambacq 2 evaluated serum prolactin levels 20 minutes after a behavioral seizure-like event in 200 patients undergoing video-EEG recordings in an epilepsy monitoring unit. Using the video-EEG as the "gold standard," they found prolactin to be elevated in all 22 patients with tonic-clonic seizures, 27 of 32 patients with complex partial seizures, and 42 of 146 patients with psychogenic seizures. For tonic-clonic seizures sensitivity was 100% and for complex partial seizures sensitivity was 84.4%. Overall, elevated prolactin occurred in 84.4% of patients with epileptic events and 28.8% of patients with nonepileptic events. Sensitivity and specificity in this study were comparable to the pooled sensitivity (52.6%) and specificity (92.8%) for all epileptic seizures in a previously published American Academy of Neurology Therapeutics and Technology Assessment Subcommittee review of 10 studies. 3 Because the present study includes a large number of patients evaluated at a single center, it provides useful new information on the utility of serum prolactin as a marker for seizures. Certain study limitations need to be considered. As the authors indicate, the study was retrospective and was performed in a selected population of patients referred to an epilepsy monitoring unit. Obtaining prolactin assay 20 minutes after a seizure in the outpatient setting is difficult, although possible by a finger-stick method. 4 Some conditions that can elevate serum prolactin, such as syncope, 5 are not well represented in video-EEG monitoring populations. The criterion used in this study for identifying elevated serum prolactin is debatable, because different studies 3 require either a doubling over baseline or elevation above some absolute value ranging from 16.5 to 45 ng/mL. The absolute value matters; for example, a doubling of serum prolactin from 1 to 2 ng/mL would not represent an impressive increase. My own view is that prolactin should at least double and achieve a minimum value of 15 ng/mL in order to meet criteria for marking an epileptic seizure. Conditions that affect baseline serum prolactin, such as dopaminergic or neuroleptic medications, pregnancy, or pituitary abnormalities, should be excluded. The main debatable issue with the findings of this study is the conclusion that "serum prolactin levels do not provide any additional support for distinguishing psychogenic non-epileptic seizures from epileptic seizures." This is an interpretive matter of glass half-full or half-empty. This gloomy interpretation is not supported by the sensitivity and specificity reported in the study. In an epilepsy moni...

To determine the usefulness of prolonged head-up tilt in the diagnosis of neurally mediated syncope, 201 patients with history of syncope of unknown cause and 102 age and gender matched control subjects underwent a 40 minute 60 degrees head-up tilt test. Head-up tilt elicited syncope (i.e., was positive) in 74 of the 201 patients (37%) with a history of unexplained syncope and in only 6 of the 102 controls (6%). The specificity of the test was 100% in patients 60 years of age and older. Symptoms during tilt-induced syncope were identified by the patients as similar to those they had suffered during their spontaneous episodes. All 80 subjects who had tilt-induced syncope recovered without sequelae. The positive predictive value of a positive responses to head-up tilt was 93% and the negative predictive value was 43%. The results indicate that the prolonged head-up tilt test is a very specific procedure of high diagnostic value in patients with a history of unexplained syncope. It is particularly useful in the elderly age groups who have a high incidence of syncope.