Startle Epilepsy. Startle-induced Seizures.
Incidence
The prevalence is very low. It affects both male and female the same.
Clinical Characteristics
Startle epilepsy is a type of reflex epilepsy in which seizures are provoked by loud noises or sudden surprises. It is considered an epileptic syndrome. Most patients with startle epilepsy are only sensitive to one sensory modality (i.e. temperature, taste, sound, pressure); however, it is the unexpected nature of the stimulus, rather than the sensory modality, that is the distinguishing feature. The seizures are frequent, usually lasting less than 30 seconds and consisting of a startle response followed by a brief but characteristic tonic phase, which is asymmetrical in 25% of patients. Many subjects fall, and clonic jerks may occur. Injury is common when the seizures occur in patients who are standing or able to fall while seated, or while they are in bathtubs or similar risky locations. Repetition of the stimulus will induce transient habituation. Patients with startle epilepsy usually have other evidence of localized or diffuse static encephalopathy, such as hemiparesis or developmental delay of different etiologies. Startle epilepsy often occurs with Down syndrome. In hemiparetic patients, the seizure starts with flexion and abduction of the paretic arm and extension of the ipsilateral leg, which rapidly involve the contralateral side. Marked autonomic manifestations, automatisms, laughter, and jerks may occur concurrently. Atonic or myoclonic startle seizures are less common. Spontaneous seizures occur, reportedly in all cases, but may be infrequent. Startle-induced seizures are frequent, occurring many times a day, and sometimes progress to status epilepticus. The insult typically occurs within the first 2 years of life and is often pre- or perinatal. Brain imaging may show localized lesions (mesial hypodensity) or diffuse lesions. The lateralized lesions usually involve sensorimotor and premotor cortex and white matter, but normal scans have been reported without neurologic deficit. Such patients have precentral or perisylvian dysplastic lesions on MRI. Schizencephaly has also been found. Startle epilepsy usually occurs in patients with severe preexisting encephalopathies, and usually only incomplete or temporary seizure control can be achieved. These patients, with intractable epilepsy, identifiable brain lesions, and neurologic and developmental abnormalities, have significantly increased mortality compared to the general population.
Precipitants
Seizures are precipitated by sudden stimulus or startle. Most patients with startle epilepsy are only sensitive to one sensory modality (i.e. temperature, taste, sound, pressure); however, it is the unexpected nature of the stimulus, rather than the sensory modality, that is the distinguishing feature.
Provocation Tests
Most patients with startle epilepsy are only sensitive to one sensory modality (i.e. temperature, taste, sound, pressure); however, it is the unexpected nature of the stimulus, rather than the sensory modality, that is the distinguishing feature.
Diagnostic Procedures
It is a clinical-EEG diagnosis. Seizures are stimulus triggered. It is the unexpected nature of the stimulus, rather than the sensory modality, that is the distinguishing feature.