**6. Comorbid sleep disorders in epilepsy**

Many patients with epilepsy complain of excessive daytime sleepiness (EDS), with reported prevalence as high as 16.9%–28% [46–48]. In fact, EDS is the most common complaint of subjects referred to sleep disorder centers. EDS in epileptic patients may result from nocturnal seizures, sedative effects of antiepileptic drugs, poor sleep hygiene, and co-morbid primary sleep disorders [49]. EDS in these patients is often mistakenly attributed to AED adverse effect rather than to an underlying primary sleep disorder.

More than 50% of the epileptics suffer from insomnia up to certain extent, as a result of adverse effects of AEDs, substance abuse, nocturnal seizures, and comorbid anxiety and depression. and out of these 43% has poor seizure control and significant impact on quality of life [50].

Co-morbid primary sleep disorder should be sought and treated, but the exact incidence of primary sleep disorders in patients with epilepsy remains uncertain.

Obstructive sleep apnea (OSA) is the most common cause of sleep-disordered breathing and may exacerbate seizure burden in as many as 33% of patients with medically intractable epilepsy undergoing pre-surgical planning [51, 52]. Predisposing factors for OSA are older age, male, obesity, dental mal-occlusion and Crowded upper airways [53].

Polytherapy AEDs in patients with drug-resistant epilepsy are at increased risk of obesity as compared to monotherapy. Anti-seizure drugs including valproic acid, pregabalin, perampanel, gabapentin and vigabatrin are associated with weight gain, therefore, can potentially worsen or increase the risk of OSA [54]. Adults who developed epilepsy later in life or had worsening seizure control, had a higher apnea–hypopnea index (AHI) and Epworth Sleepiness Scale (ESS) score compared with those who were seizure-free or had an improvement in seizure control [52]. Nasal continuous positive airway pressure (CPAP) therapy demonstrated seizure reduction in patients with OSA and refractory epilepsy in several observational studies [55–59].

Restless legs syndrome (RLS), which is defined as the urge to move the legs that improve or partially relieves with activity, worsen with inactivity and is worse at night, is common feature in epileptics with a prevalence of 10.2%–28.2% [48, 60].
