Workup of New-Onset Seizures
Seizures are one of the most common complaints in neurological practice. The estimated incidence of a single unprovoked seizure is 23–61 per 100,000 person-years. Approximately 30% will recur in the first 5 years and meet the diagnostic criterion for epilepsy, specifically, two or more unprovoked seizures.
The initial evaluation of the first seizure is critical in establishing the correct diagnosis and etiology and determining the likelihood of recurrent events. It is the likelihood of recurrent events that helps to frame the decision of whether or not to initiate treatment after a single event. With the evaluation also comes an educational opportunity with the patient and family regarding seizure first aid and seizure precautions.
Not everything that looks and acts like a seizure is in fact an epileptic seizure (Chapter 5). The differential diagnosis of paroxysmal spells is quite broad, including seizure, syncope, psychogenic nonepileptic spells, migraine, movement disorders, transient ischemic attack (TIA), and toxic–metabolic disturbance. Pediatric populations have additional considerations including breath-holding spells, febrile seizure, and self-stimulating behaviors typically in developmentally delayed children. Nocturnal spells may also represent parasomnias. A good history can narrow down the differential diagnosis, although video–EEG recording of a typical event may be required for definitive diagnosis. Three of the more common seizure mimics seen in practice are highlighted in the succeeding text. Psychogenic nonepileptic events are covered in Chapter 6.
Syncope is defined as a loss of consciousness and postural tone caused by cerebral hypoperfusion with spontaneous recovery. Twelve percent of patients with syncope have an associated convulsion termed a post-syncopal convulsion that can be confused with an epileptic seizure. In a video study of clinical features of induced syncope, the most common finding was myoclonus, and less frequent findings were automatisms and head turn. Features of the history suggesting syncope include preceding pallor, sweating, light-headedness, diminution of hearing and vision, and chest pain. Postural triggers and changes in blood pressure or heart rate preceding or during the event also are suggestive.
Migraine headaches may have associated visual or sensory auras that can overlap with symptomatology seen in focal seizures. Migraine auras are more prolonged than epileptic auras and can last minutes to hours in comparison with epileptic auras, which are usually seconds in duration. Visual auras tend to be flickering, black and white zigzags in migraine, whereas in focal seizures involving visual cortex, visual phenomena are usually bright and multicolored. Sensory auras, including tingling or numbness, can be present in both but typically spread more slowly in migraine compared with seizure, which generally has a fast, marching anatomic spread.
Transient ischemic attacks (TIA) usually present with negative symptoms that vary depending on the vascular territory involved. Although seizures are typically associated with positive symptoms, there are specific seizure semiologies that may clinically overlap with a TIA, including isolated intermittent aphasia, which can represent focal ischemia or a focal seizure of the dominant hemisphere. Todd’s paresis, consisting of focal weakness following a seizure, can often be confused for a stroke if the preceding seizure is not witnessed.
Clinical history and examination
One of the most important initial steps in the evaluation of new-onset seizures is a detailed clinical history and examination. Obtaining a clinical description of the events is the first step in determining the etiology of events. Information should be obtained from the patient when possible as well as from other individuals who have observed the event of interest. The patient’s recollection may be limited by alteration in consciousness or postictal confusion, and observer reports can be unreliable. Chapter 5 details the process by which the history and examination can be used at the bedside to establish whether an individual’s events are seizures.
The clinical background in which the seizure occurred can help determine etiology. A history of prodromal fever may suggest an infectious etiology. Care must be taken not to overinterpret fever at the time of acute seizure presentation, as a seizure itself may cause transient hyperthermia. A history of alcohol or drug use can raise suspicion for alcohol withdrawal or drug overdose, respectively.
A detailed medical, family, and social history may clarify the likelihood that the index event is a seizure by discerning whether the patient has any seizure risk factors, which may increase the individual’s likelihood of seizure above that of the general population.
Depending on how soon the clinical examination is performed after the index event, the patient may still experience postictal confusion or fatigue, limiting the ability to perform a thorough neurological examination. In this setting, focus should be placed on the presence or absence of focal or lateralizing findings such as focal motor weakness, reflex asymmetry, or plantar responses that can provide evidence for a focal onset.
No single test can replace history taking and physical examination in diagnosis and evaluation of a first seizure; however, diagnostic procedures such as neuroimaging or electroencephalogrphy (EEG) can provide supportive data for diagnosis and prognosis.
There has been ongoing debate regarding the necessity of EEG for evaluation of a first seizure, although the 2007 American Academy of Neurology (AAN) practice parameter for adults and 2000 AAN practice parameter for children both recommend routine EEG in this setting. Specifically, the value of EEG is largely twofold: (1) it allows individual prediction of seizure recurrence and (2) it identifies patterns consistent with specific epilepsy syndromes. Approximately 30% of EEGs obtained to evaluate initial seizure are abnormal. Consistently, an abnormal EEG and an identified etiology are associated with an increased risk of seizure recurrence. More specifically, the abnormal findings of generalized or focal epileptiform discharges are associated with an approximately two times greater risk of seizure recurrence. Therefore, the presence of these discharges may prompt initiation of antiepileptic medication even after the first event. Chapter 7 further discusses EEG procedures and indications and common findings seen in patients with epilepsy.