Statistical Process Control (SPC)—A simple objective method for monitoring seizure frequency and evaluating effectiveness of drug interventions in refractory childhood epilepsy

Abstract

Objective assessment of seizure fluctuation in patients with refractory epilepsy in the clinical setting is difficult and subjective assessment may lead to inappropriate changes in medication. We therefore evaluated the utility of Statistical Process Control (SPC) charts as a simple objective clinical tool to demonstrate variability in seizure frequency and to assess the efficacy of drug interventions. Total weekly seizure frequencies over 1 year were collected for 38 young people with refractory epilepsy. SPC I-charts were generated and Nelson's tests for "special" causes of variability applied. In a separate analysis, run charts were reviewed by two epileptologists blinded to clinical data who were asked to identify if and when drug interventions took place. The SPC charts showed that only seven out of 38 (18%) patients had stable seizure frequencies. In the others, they identified significant but short-lived increases in seizure frequency, which were followed by rapid return towards baseline independently of drug changes. A substantial reduction in seizure frequency was associated with a drug increase in only 5 (6.5%) instances. Inter-rater agreement on whether there were drug interventions and their timing was poor (κ=0.15, p=0.4). SPC I-charts have the potential to be used as a clinical tool to monitor seizure frequency and to evaluate efficacy of drug interventions in patients with refractory epilepsy. Epilepsy is commonly an unstable condition with fluctuations in seizure frequencies which are unpredictable and usually do not require a change in treatment. Positive responses to treatment changes are uncommon.