Is treatment in adults with intellectual and developmental disability also suffering from epilepsy different from adults with uncomplicated epilepsy?

Adults with an intellectual and developmental disability (IDD) comprise a significant proportion of the prevalent epilepsy population [1]. Despite the variation in reported prevalence, it is clear that the prevalence of epilepsy is high in people with IDD. The prevalence of epilepsy is also related to the level of IDD. In 29 studies which included all levels of DD, the pooled estimate was 22.2% [95% confidence interval (CI) 19.6%–25.1%] whilst for four studies with samples skewed towards less severe IDD the pooled estimate was 7.3% (95% CI 4.5–11.6%) and for five studies skewed towards more severe IDD the pooled estimate was 41.6% (95% CI 32.1–51.8) [2]. Seizures in this population are often complex and refractory to treatment and antiepileptic medication may have a profound effect upon behaviour [3,4]. In adulthood, patients with IDD and epilepsy (IDD-E) have neurological, psychiatric, medical and social comorbidities compounded by fragmented and limited care [5] Hence, patients with IDD-E compose a major portion of the ‘hard to treat’ adult epilepsy population [6]. In this issue, Doran and colleagues [7] conducted a comprehensive search to identify evidence for prescribing commonly used antiepileptic drugs (AEDs) in adults with IDD including genetic syndromes specifically associated with epilepsy. The literature review which was based on PRISMA guidelines revealed 43 studies relevant for the purpose of this study. The authors did not identify any studies taking into account the response to AEDs in the IDD population based on WHO Diagnostic and Statistical Manual of Mental Disorders criteria of clinical severity of IDD. The authors found no specific evidence to help ascertain if certain AEDs perform better or worse from efficacy as well as side effect profile in the population with IDD compared to the general population. Whilst treatment guidelines have suggested that the newer AEDs tend to be better tolerated and affect cognitive functioning to a lesser degree than older AEDs, the evidence base applied to people with IDD as shown by this study is extremely weak. An unblinded randomized control trial with a large sample size randomized to a number of AEDs (SANAD trial) provides the most accurate comparison in people without IDD for side effect profile and quality of life [8]. However, no similar study has been conducted in people with IDD-E. The authors highlighted that the available literature demonstrates that, whilst treatments can be very effective against seizures, patients with IDD-E can respond with significantly more adverse behavioural, physical and psychiatric reactions than in the general population. Impairment in cognition, behaviour and coordination due to AEDs may be wrongly attributed to the underlying IDD, termed ‘diagnostic overshadowing’ [5]. Fourteen randomized controlled studies with 1116 patients with IDD-E studied carbamazepine, clobazam, felbamate, gabapentin, lamotrigine, rufinamide and topiramate [4]. No features distinguished a particular AED with respect to efficacy or side effects. The Cochrane reviewers advised making epilepsy care decisions based on aetiology and standard practice, not the IDD. The evidence suggests that adverse events are similar to those in the general population and that behavioural adverse events leading to discontinuation are rare; however, several adverse effects are under-reported [4]. Less vigorous studies have yielded similar, often mixed, results [5]. AEDs with potential benefits on comorbid mood disorders in IDD-E based largely on anecdotal observations include valproate, lamotrigine and oxcarbazepine [5]. Successful care of adults with IDD-E depends on applying recent advances in genetic evaluation, ongoing epilepsy and impact of treatment, collecting accurate data, addressing psychological comorbidity and optimizing care transition [5]. In general, proper epilepsy treatment is essential for better overall outcome. The challenge in treating IDD-E is that seizure types and epilepsy syndromes, as well as their effective treatments, are varied. There is no ‘one-size-fits-all’ AED that controls all seizure types with equal efficacy. The consensus guidelines into the management of epilepsy in adults with an intellectual disability highlight the dearth of high-quality evidence from well-constructed studies on which to base guidance [6]. There is a mandate for those who fund as well as those who deliver healthcare to