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[A comparative study of three systems for quantifying the spike and wave index in patients with continuous spikes and
G Azcona1, I G Gurtubay1, A Mosquera1
1Complejo Hospitalario de Navarra , Pamplona, Espana.
Introduction:
Continuous spikes and waves during slow sleep (CSWS) is an epileptic encephalopathy of childhood with a pattern of epileptiform discharges during sleep, which, if prolonged over time, produce severe neuropsychological impairment. Quantification of the paroxysms by means of a spike and wave index (SWI) > 85% establishes a presumptive diagnosis and allows early therapy to be started to prevent such impairment.
Aims:
To compare the results of the classic method for calculating the SWI against two proposals that optimise the relation between the analysis time employed and the diagnostic sensitivity.
Patients And Methods:
The nocturnal electroencephalographic registers of 17 patients with CSWS were studied. Two observers calculated the SWI with the classic method, as well as with two other methods, M2 and M3, first in the active phase and then in the remission phase. The time required by each method, the individual SWI values and the agreement between methods and observers were compared.
Results:
With M3 two of the patients failed to reach the cut-off point of SWI > 85%. Agreement in the active phase of CSWS after M2 and M3 was 0.762 and 0.704, respectively, while in the remission phase it was 0.951 and 0.830. Inter-observer agreement exceeded 0.905 in all cases.
Conclusions:
The two abbreviated methods can be used in both the active and the remission phases, with a substantial reduction in the analysis time that is needed. Our results support the current tendency to consider SWI > 60% as suggestive of CSWS. Method M2 yields results that are closer to those of the classic method than those of M3.
