Prevalence and Incidence of Drug-Resistant Mesial Temporal Lobe Epilepsy in the United States. 
We reviewed data on the epidemiology of epilepsy in the United States and estimated the prevalence and incidence of drug-resistant temporal lobe epilepsy (TLE) due to hippocampal sclerosis (HS) based on extrapolation from the available data drawn from the literature.  We searched the electronic database PubMed on December 14, 2016, using the following search terms in the title: "epilepsy" OR "temporal lobe" OR "hippocampal sclerosis" AND "epidemiology" OR "prevalence" OR "incidence."  Relevant original studies were included.  We also reviewed several previous systematic reviews, meta-analyses, and their references.  We concluded that the estimated current U.S. prevalence of drug-resistant HS-TLE is 0.51-0.66 cases per 1000 people, and the estimated U.S. incidence is 3.1-3.4 cases per 100,000 people per year.  Based on a U.S. population of 324 million, we estimate that as many as 143,000-191,000 U.S. patients still suffer from drug-resistant HS-TLE and are in need of surgery or other therapeutic options.  Although full scale epidemiologic studies on drug-resistant HS-TLE are needed, several observational studies allow adequate estimates of the range for the incidence and prevalence of this condition.  Given the morbidity and mortality associated with poorly controlled seizures, this relatively large and growing patient population is a matter of concern.  Considering the variety of treatment options that are available or in the pipeline to treat drug-resistant epilepsy, future efforts should focus on advocating for early referral of patients with drug-resistant HS-TLE for more comprehensive epilepsy management.