Effect of color of flash stimulus on variability of flash visual evoked potential latencies.

Visual Evoked Potentials (VEPs) are evoked potentials generated in response to visual stimuli. The flash VEP (FVEP) is used less frequently than pattern-reversal VEP (PR-VEP) because; it shows great variations in both latency and amplitude in normal subjects. The advantage of FVEP is its feasibility in non-cooperative subjects, which circumvents the major limitation of PR-VEP. The present study was undertaken to assess the effect of change of color of flashlight on variability of FVEP latencies. Healthy subjects in the age group of 18-30 years underwent the standard stimulus using white light, followed by altered stimuli done with red and blue light. 2 trials were given for each eye, for each type of stimulus. The same set of studies was repeated at the same clock time the following day. The inter-individual and intra-individual variability in the peak latency of P2 and N2 waveforms was assessed using coefficient of variation (COV). Both inter-individual and intra-individual variability was less when monochromatic light was used. Between red and blue FVEP, inter-individual variability was less in blue FVEP and the results of intra-individual variability was inconclusive. Monochromatic stimulation preferably with blue light reduced both inter-individual and intra-individual variability seen in latency of P2 and N2 waveforms in FVEP and hence recommended in preference to standard white stimulus for FVEP recording.

Severe phenytoin toxicity in a CYP2C9FNx013FNx013 homozygous mutant from India.

The authors report an Indian adult female patient with a history of generalized tonic clonic seizures who developed severe features of phenytoin (DPH) toxicity on therapeutic dosage of this antiepileptic drug. Administration of 300mg/day of DPH in this patient resulted in toxic symptoms associated with an excessive serum DPH concentration of 33mug/ml. The PCR-RFLP analysis revealed a homozygosity involving CYP2C9FNx013FNx013. This mutation results in a marked decrease in the enzymatic activity (CYP2C9) and leads to a decreased clearance of the drug which can lead to severe acute and chronic toxicity. On switching the antiepileptic therapy from DPH to sodium valproate, there was reversal of both.

Tilt table testing in the diagnostic evaluation of presyncope and syncope: a case-series report.

Tilt table testing has long been used as a standard tool in the diagnostic evaluation of syncope. However, differences of opinion exist with regard to its utility in the evaluation of patients with only presyncopal attacks. We present the results of drug-free, 70-degree head-up tilt table tests (maximum duration of 45 minutes), conducted between May 2002 and May 2003 in the Department of Physiology at JIPMER. This series consisted of both male and female patients (age 6-79 yr) with presyncope (n = 43), unexplained syncope (n = 43) and asymptomatic healthy volunteers without a history of syncope (n = 14). 28 out of 43 patients with unexplained syncope had a history of recurrent syncope while the remaining 15 had only 1 episode. 2 out of 43 patients (4.6%) with a history of only presyncopal attacks had a positive test (induction of intense presyncope and/or syncope accompanied by hypotension and/or a relative bradycardia). 21 out of 43 patients (49%) with a history of syncope had a positive test. 7 had vasodepressor syncope due to hypotension, 6 had cardioinhibitory syncope characterized by asystole and 10 had a mixed form of the vasovagal syndrome characterized by hypotension as well as bradycardia. 18 out of 28 patients (64%) with recurrent unexplained syncope had a positive test. All fourteen healthy volunteers had a negative test. We conclude that tilt table testing is useful in the diagnostic evaluation of patients with unexplained syncope, especially those with recurrent syncope, but not in the evaluation of patients with presyncope alone.