Tonic-clonic seizures from sleep are usually easily diagnosed if collateral history is available from a bed partner or another witness. The characteristic progression of a tonic-clonic seizure is well described.¹ There may be an initial cry, followed by jaw clenching and cessation of respiration associated with tonic limb extension in which the limbs are usually extended. This tonic phase is followed by clonic jerking of the limbs, usually symmetric in nature, ending with a deep inspiration and subsequent stertorous breathing. A tonic-clonic seizure usually lasts 1.5 to 2.5 minutes. After the seizure, there is initially stupor, followed by confusion lasting minutes. Often this is followed by a return to sleep.

Even if no witness account is available, tonic-clonic seizures may be associated with tongue biting (usually on the lateral aspect) and urinary incontinence; evidence of such features on waking should raise the suspicion that a tonic-clonic seizure occurred, particularly if associated with generalized myalgias and unusual fatigue, headache, amnesia, or malaise.

Complex partial seizures arising from the frontal lobes can cause diagnostic confusion, because the features range from subtle to dramatic or bizarre.² Most individuals with frontal lobe epilepsy (FLE) have a significant proportion or all of their events during sleep. NFLE is the diagnosis if 90% or more of the seizures arise from sleep. Frontal lobe complex partial seizures are usually characterized by an abrupt, often explosive-onset, awakening of the patient from non–rapid eye movement (NREM) 2 sleep accompanied by sustained asymmetric dystonic, tonic posturing, violent hypermotor behaviors, thrashing, pedaling, and/or kicking of the lower extremities. Patients are often aware during the seizure, but say they cannot control their movements or vocalizations.

Other motor automatic movements (automatisms) that may be seen include prominent bimanual and bipedal movements, such as bicycling or kicking movements of the legs, hand clapping, and/or leg slapping. Some stand, walk, or run during the seizure, although they rarely wander far. Axial body movements, such as rocking, thrashing, running (often in an apparently agitated or distressed manner), sitting up, and head nodding are also common. Automatisms in some patients have a semipurposeful quality.³ Sexual automatisms, such as pelvic thrusting and genital manipulation, are sometimes observed.⁴

Vocalization is common, and often consists of unintelligible screaming or moaning. Some individuals exhibit palilalia (repeating their own words) or scream obscenities; others breathe strangely but without vocalization.³ The seizure often wakes the patient from sleep, and consciousness may be preserved during it. Some report that a brief aura wakes them, often nonspecific or sometimes an unpleasant choking sensation.⁵ Although some complex partial frontal lobe seizures may include tonic postures or clonic movements, reflecting involvement of the supplementary motor area or primary motor cortex respectively, many do not and are characterized by automatisms only.

The seizures of NFLE are often characterized by paroxysmal attacks of increasing complexity and duration. Minor attacks are characterized by stereotyped limb, axial musculature, and/or head movements that typically last 2 to 4 seconds.² Paroxysmal arousals consist of abrupt, stereotyped arousals from sleep accompanied by trunk and head elevation often with vocalization and frightened expression that often last only 5 to 10 seconds. Major attacks (formerly called nocturnal paroxysmal dystonia) typically last 20 to 30 seconds and are characterized by stereotyped asymmetric tonic or dystonic posturing, bizarre hyperkinetic behaviors, bipedal automatisms, axial movements of the trunk and pelvis, vocalization, and tonic or dystonic posturing. Episodic nocturnal wanderings are uncommon, characterized by agitated ambulation, screaming, and sometimes semipurposeful automatisms.⁶

Patients rarely have a single type of attack. Smaller episodes are usually considered fragments of larger seizures,² and all events are considered to be manifestations of the same underlying epileptic process.⁷ These can be difficult to distinguish from nonepileptic arousals.⁸ They may occur repetitively and frequently throughout the night, and are often underreported, with some individuals being unaware of the episodes.²

Between 50% and 80% of patients with temporal lobe epilepsy (TLE) report that some of their seizures occur during sleep,⁹ although seizures in TLE more often occur when awake. Secondarily generalised tonic clonic seizures (GTC) in TLE occur most often during sleep, with partial seizures more common in wakefulness. Exclusively nocturnal TLE is uncommon.¹⁰ Individuals with nocturnal TLE are usually woken by a typical temporal lobe aura (autonomic, experiential, or special sensory) that progresses to a complex partial seizure characterized by expressionless staring with minor oral or limb automatisms. Although TLE should be considered in the diagnosis of paroxysmal nocturnal events, in my experience, diagnostic difficulty is less common than for FLE because they usually have seizures awake, interictal epileptiform discharges (IEDs) awake and asleep, and their seizures are accompanied by ictal electroencephalogram (EEG) patterns.

Tonic seizures occur predominantly in individuals with learning disability and symptomatic generalized epilepsy, particularly Lennox-Gastaut syndrome (LGS). LGS most often appears between ages 2 and 6 years, is characterized by frequent daily seizures of multiple types, and is usually accompanied by developmental delay and psychological and/or behavioral problems. Tonic seizures are the most frequently occurring seizure type in LGS, 90% of which occur during sleep. These seizures are typically brief, lasting only seconds, and are characterized by symmetric or asymmetric posturing of the upper limbs, often with involvement of the neck, trunk, and lower limbs. They usually occur in clusters during sleep (affected individuals may have dozens of tonic seizures per night), and less often in wakefulness. Tonic seizures do not usually present diagnostic challenges, although occasionally are subtle and only recognized on video-EEG monitoring.

NREM arousal disorders are the most frequently encountered parasomnias and the most likely to cause diagnostic confusion with epilepsy. They are characterized by paroxysmal motor behaviors, without conscious awareness, usually occurring during stage 3 or 4 NREM sleep (rarely NREM 2). They have a broad spectrum of clinical manifestations, and are loosely subdivided into 3 main forms, albeit with significant overlap.⁸ Confusional arousals are associated with sudden arousal and a period of apparent confusion, but little motor or autonomic involvement. Somnambulism (sleepwalking) is associated with motor activity, typically walking, but also other semipurposeful tasks such as moving objects, talking nonsensically, dressing, eating, and drinking,¹³ but with little autonomic or affective involvement. Sleep terrors (pavor nocturnus) are dramatic events characterized by prominent autonomic and affective features; the individual suddenly arouses from deep sleep, usually with a terrified scream, appearing agitated and frightened, with tachycardia and diaphoresis.

NREM arousal parasomnias vary in duration, lasting from 1 or 2 minutes to longer than 30 minutes. They tend to begin in early childhood, and are common; an estimated 15% to 20% of children¹⁴ have at least 1 episode of sleepwalking. Although resolution in adolescence is typical, they persist in an estimated 1% to 4% of adults.¹⁵ NREM arousal parasomnias are thought to arise through incomplete or impaired arousal from deep NREM sleep,¹⁶ resulting in a dissociation between sleep and wake states.¹⁷ Because of their high prevalence in otherwise normal children, they are considered to represent altered physiologic processes during brain maturation rather than true abnormality. In some cases, an underlying process causing frequent arousals (such as obstructive sleep apnea [OSA]) may precipitate parasomnias,¹⁸ or the use of drugs that increase the intensity of slow wave sleep (gabapentin, sodium oxybate).¹⁹

REM sleep behavior disorder (RBD) is characterized by a loss of muscle atonia during REM sleep resulting in the acting out of dream content (oneiric behaviors). During REM sleep, patients display complex and often violent behaviors such as screaming, punching and kicking, jumping out of bed, and running.²⁰ These behaviors may result in injury to the patients or their bedpartners.²¹ Individuals can usually be wakened from these episodes, when they may report vivid, disturbing dreams.²² Episodes may last from a few minutes to half an hour, and although some patients have episodes several times per night, in others they are less frequent. Events occur preferentially in the second half of sleep, when the greatest proportion of REM sleep occurs.²³ Recent studies show that the motor movements in RBD are typically brief: 75% lasted less than 2 seconds, 83% were simple, 14% complex, 11% had vocalizations, and only 4% were violent. The motor behaviors of RBD tend to (1) be more severe at the end of the night when most REM sleep occurs; (2) be more in phasic (than tonic) REM sleep; (3) exhibit night-to-night variability (but not for REM sleep without atonia); (4) most often be limb jerks (most often of the arms); (5) usually not involve leaving the bed; and (6) often feature no apparent increase in the heart rate during episodes (perhaps because of loss of heart rate variability).^24–27 A strong association between chronic RBD and degenerative neurologic conditions, particularly Parkinson disease (PD) and multiple system atrophy (MSA), has been reported,^20,21 RBD often preceding parkinsonian features by several years.²⁸ RBD mainly affects individuals more than 50 years of age,²⁰ with men affected in more than 80% of large reported series.²¹

Other parasomnias, including sleep paralysis, may occasionally be considered in the differential diagnosis of epilepsy, but their presentation is so characteristic that diagnostic confusion should not occur. Sleep paralysis is characterized by episodes of absent voluntary motor activity at sleep onset or waking, usually lasting for a few minutes. Individuals are aware but paralyzed, and may experience vivid hallucinations. The episodes may subside spontaneously, and may be aborted if the individual is touched.²⁹ Sleep paralysis is thought to represent an intrusion of REM sleep into wakefulness. It may occur in otherwise normal individuals, particularly after a change in sleep pattern or sleep restriction,³⁰ but is also a feature of narcolepsy with cataplexy.

Periodic limb movements during sleep (PLMS) are characterized by repetitive and stereotyped movements of the legs (extension of the great toe and dorsiflexion of the ankle), predominantly during NREM sleep; occasionally the upper limbs may be involved. However, from a diagnostic perspective, PLMS are usually not confused with epilepsy because the interval between jerks is too long.