John R. Gates

INDUCTION OF SPEECH ARREST AND COUNTING ERRORS WITH RAPID-RATE TRANSCRANIAL MAGNETIC STIMULATION

Six adult epileptic patients underwent rapid‐rate transcranial magnetic stimulation (rTMS) at stimulation rates of up to 25 Hz with an 11‐cm water‐cooled round coil held flat on the scalp, centered over 15 different positions on each side of the scalp. The trains of stimuli were for 10 seconds while the patients counted aloud. rTMS centered over D5 or D7 induced reproducible speech arrest in all patients and counting errors in three when applied at lower intensities. There were no such speech disturbances by rTMS centered over the different positions on the right side. Intracarotid amobarbital test (IAT) demonstrated left hemispheric language dominance in all patients. Lateralization of speech arrest induced by rTMS correlated with the IAT results and may be helpful for noninvasive determination of hemispheric language dominance. NEUROLOGY 1991;41:697‐702

Vagus Nerve Stimulation in Children with Refractory Seizures Associated with Lennox–Gastaut Syndrome

Summary:  Purpose: Vagus nerve stimulation (VNS) is approved for use for refractory partial seizures. Nevertheless, information regarding VNS therapy for special populations, including Lennox–Gastaut syndrome (LGS) is limited. We discuss the effectiveness, tolerability, and safety of VNS therapy in patients with LGS.

The Effects of Adjunctive Topiramate on Cognitive Function in Patients with Epilepsy

Summary:  Purpose: We investigated possible cognitive effects of topiramate (TPM) in polypharmacy on patients with intractable epilepsy.

Transcranial magnetic stimulation in patients with epilepsy

We studied the effects of transcranial magnetic stimulation (TMS) applied in trains of 8- to 25-Hz stimuli on electroencephalographic epileptiform activity on eight patients being evaluated for epilepsy surgery. We performed the stimulation with a round water-cooled stimulation coil held flat on the scalp and centered over different positions of the International 10-20 System. We were unable to trigger seizures or induce epileptiform discharges arising from the epileptic focus in any of the eight patients with any of the stimulation protocols. However, we induced a partial motor seizure from the contralateral hemisphere to the exclusive temporal focus in the only patient stimulated with 100% maximal intensity. Precautions have to be taken when applying rapid TMS to patients because of the risk of seizure induction. Our results do not support the view that TMS specifically activates the epileptic foci.

Causes and Management of Hyponatremia

OBJECTIVE: To review clinical information on the incidence and causes of hyponatremia (defined as a serum sodium level <130 mEq/L), the most common electrolyte abnormality seen in general hospital patients, and to discuss the diagnosis and treatment of hyponatremia in relation to these factors. DATA SOURCES: Primary sources and review articles were identified via MEDLINE (1981–July 2003) for entries on hyponatremia. We limited the search to specific topics including incidence, risk factors, diagnosis, treatment, and clinical disorders and medications associated with hypotonic hyponatremia. STUDY SELECTION AND DATA EXTRACTION: All of the articles identified were evaluated, and relevant and representative information was included in this review. DATA SYNTHESIS: Hyponatremia can result from several disease states, injury, surgery, physical exercise, or the administration of certain drugs (e.g., antidepressants, antiepileptics) and is associated with advanced age. Drug-induced hyponatremia is often asymptomatic and usually resolves following water restriction and monitoring of medication. Symptoms of hyponatremia are primarily neurologic; the principal danger of hyponatremia relates to effects on central nervous system function due to changes in brain size. CONCLUSIONS: Although hyponatremia can be a serious condition, appropriate measures for the management of at-risk and affected patients will lead to full recovery in most cases.

Corpus callosotomy: clinical and electroencephalographic effects

Summary: Six persons (five male, one female), 15–41 years of age (mean, 23 years), with medically intractable epilepsy for 7–35 years (mean, 15 years) underwent total corpus callosum section (anterior commissure to posterior commissure) for treatment of seizures resulting in falls and injuries. Preoperative EEGs demonstrated two or more morphologically distinct interictal discharges, at least one of which was generalized. Generalized ictal EEG discharges were documented in all cases to account for the clinical seizures resulting in injury. A comparison of generalized epileptiform discharges in comparable states of arousal pre‐ and postoperatively demonstrated a statistically significant (p < 0.05) reduction of generalized discharges after surgery. Postoperative observation periods have ranged from 10 to 30 months (mean, 17.6 months) and have documented a statistically significant (p < 0.05) decrease in the number of falling seizures (means: preoperative, 23.2 seizures/month; postoperative, 0.7 seizures/month). A statistically significant difference in pre‐ and postoperative total (generalized and focal) interictal discharges was not demonstrated. Long‐term, clinically apparent complications of surgery did not occur in our patients. Thus, sectioning of the corpus callosum interrupts generalized epileptiform discharges (as documented by the postoperative EEG) and usually results in a significant decrease in generalized seizures.

Response of multiple seizure types to corpus callosum section.

Summary: Twenty‐four patients (16 men, 8 women) underwent corpus callosum section specifically for improvement of control of atonic or tonic seizures that resulted in falls and injuries. All patients suffered from multiple seizure types, including complex partial (CP) and tonic‐clonic (TC) seizures, in addition to the tonic or atonic episodes. Preoperative seizure frequency was quantified for all types for 1 year immediately before surgery and for the most recent year since the procedure; average monthly counts were obtained for each seizure type. The period of follow‐up since surgery averaged 43 months (range, 23–79 months). Statistically significant improvements were documented, not only for the atonic/ tonic seizures (p < 0.0001) for all patients, but also for TC seizures (17 patients; p < 0.001) and CP seizures (20 patients; p < 0.02). Six patients experienced an exacerbation of CP seizures postoperatively, and three developed new simple partial (SP) seizures. In all of the CP group and all three of the SP group, ictal video and EEG features suggested that the new seizures were an aborted expression of the previously generalized seizures. From these data, we conclude that callosotomy is an effective treatment for tonic, atonic, and TC seizures intractable to anticonvulsant medications. Three patients became seizure free. The procedure may also be useful for certain specific subgroups of CP epilepsy, but further studies are required before expanding callosotomy to intractable CP seizures not amenable to focal resection.

Lack of pathologic changes in human temporal lobes after transcranial magnetic stimulation.

Summary: Most animal studies have failed to demonstrate pathologic changes in the brain after transcranial magnetic stimulation (TMS). Nevertheless, vacuolar lesions in the cortex of rats after TMS have been reported. We report the first histopathologic studies of human brains after TMS in 2 patients with epilepsy who underwent temporal lobectomies. They had been involved in a study to determine the speech‐dominant hemisphere by TMS and had received ∼2,000 stimuli centered over the resected temporal lobe. Histologic study of the surgical specimens did not show any lesions attributable to TMS in these 2 patients.

Nonepileptic Events in Childhood

Summary: The medical records of 27 children admitted to the MINCEP Epilepsy Program for evaluation of intractable epilepsy but later shown to have nonepileptic events by EEG with simultaneous video monitoring were reviewed. Four groups were identified: pure psychogenic events (5 patients), psychogenic events plus epileptic seizures (3 patients), pure nonepileptic physiologic events (5 patients), and nonepileptic physiologic events plus seizures (14 patients). Historical data, physical examinations, and neurodiagnostic evaluations (including previous EEGs, neuroradiologic evaluations, and neuropsychologic testing) were reviewed. Children in all groups, except for those with pure psychogenic seizures, had a history of multiple seizure types identified by parents or caretakers. A history of status epilepticus was obtained in 64% (of 22 patients), including 11 of 14 patients with physiologic events plus seizures. Abnormal findings on neurologic examination were common, especially in children with nonepileptic physiologic events. AH but two patients had a history of interictal epileptiform abnormalities on previous routine EEGs. Based on identification of nonepileptic events, antiepileptic drugs (AEDs) were discontinued completely in eight patients (30%) and the total number of AEDs was reduced in nine others (33%). A diagnosis of nonepileptic events should be considered in all children with refractory seizures or multiple seizure types. Abnormal findings on routine (interictal) EEG may actually confound the diagnosis. Intensive neurodiagnostic EEG‐video recording is the preferred method for distinguishing nonepileptic from epileptic seizures.

Antiepileptic drugs and reduced bone mineral density.

There is a growing interest in recognizing the association between antiepileptic drugs and reduced bone mineral density. Although the literature regarding this association has been available for more than three decades, the management of this complication remains unclear. We review the relevant literature regarding antiepileptic drugs and reduction in bone mineral density with the aim of developing some guidelines for practical management of this problem. This review focuses on the mechanism of antiepileptic drug-induced bone loss, its recognition, and its management.