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Corresponding author at: U.O. di Neuropsichiatria Infantile, Dipartimento Materno-Infantile, Azienda Ospedaliero-Universitaria di Parma, Via Gramsci 14, 43126 Parma, PR, Italy.
Reflex Myoclonic Epilepsy shows spontaneous remission and excellent prognosis.
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A clinical identification avoids extensive investigations and anti-convulsant drugs.
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Tap seizure is related to age-dependent hyperexcitability of sensorimotor cortex.
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Tap seizure seems specific of a low level of functional segregation of the brain.
Abstract
Tap seizure is a type of reflex myoclonic epilepsy in which seizures are evoked mainly by unexpected tactile stimuli and which is classified among the electroclinical syndromes of infancy. This condition, whose onset is in the first two years of life, is characterized by excellent prognosis and is extremely rare. We reviewed all published articles and case reports on Reflex Myoclonic Epilepsies focusing on touch-induced seizures in order to clarify clinical and electroencephalographic findings. Our aim is to increase knowledge about this specific disorder in order to help pediatricians avoid extensive investigations when making their diagnosis and reassure parents regarding absence of long-term complications.
], is a rare form of electroclinical syndrome which the recent report of the ILAE Commission on Classification and terminology (2017) has categorised as infancy due to the age of onset. Seizures appear during the first 3 years of life in children with normal motor and mental development [
]. They are characterized by reflex myoclonic seizures (Reflex MS) triggered by unexpected stimuli of different types, especially auditory stimuli or combinations of auditory and tactile stimuli. Cases of reflex seizures induced by tactile-only stimulation have been reported in literature too [
Reflex seizures with somatosensory precipitation. Clinical and electroencephalographic patterns and differential diagnosis, with emphasis on reflex myoclonic epilepsy of infancy.
in: Zifkin B.G. Andermann F. Beaumanoir A. Rowan A.J. Reflex epilepsy and reflex seizures: advances in neurology. Lippincott-Raven Publishers,
Philadelphia1998: 193-206
Reflex seizures with somatosensory precipitation. Clinical and electroencephalographic patterns and differential diagnosis, with emphasis on reflex myoclonic epilepsy of infancy.
in: Zifkin B.G. Andermann F. Beaumanoir A. Rowan A.J. Reflex epilepsy and reflex seizures: advances in neurology. Lippincott-Raven Publishers,
Philadelphia1998: 193-206
Revised terminology and concepts for organization of seizures and epilepsies: report of the ILAE Commission on Classification and Terminology, 2005-2009.
]. We have reviewed all case-reports covering “Tap Seizure” in literature, and focused on the clinical and electroencephalographic features. This review may be of help to pediatricians in recognizing these specific, yet rare seizures, so as to perform a suitable differential diagnosis compared to other seizures burdened by unfavourable outcome.
2. Methods
A literature search was conducted in PubMed for reports published up April 2017, using the following search terms: “reflex myoclonic”, “tap seizure” and “touch induced seizures”, both self-staning and in combination with “epilepsy in infancy”. Articles with seizures due to inherited metabolic disorders or brain malformations and Meeting abstracts were excluded.
The information extracted from each study is reported in the table and includes year of publication, first Author’s name, sample size, seizure trigger, clinical and EEG findings, outcome and follow-up duration.
3. Clinical features
Tap seizure is a rare form of epileptic disorder that appears between the 2nd and 24th month of life in otherwise normal children with a male prevalence. To our knowledge 89 cases of RMEI are reported in literature; 2 papers (9 patients) were excluded because none had touch induced seizures, 59 patients had myoclonic seizures induced by different stimuli, with 27 cases having touch induced seizures only (Table 1). All patients were born to unrelated healthy parents following a normal pregnancy and with an uneventful neonatal-perinatal history. Febrile seizures, a positive family history of febrile seizures or idiopathic generalized epilepsies were often reported [
]. Seizures in RMEI are characterized by generalized myoclonic jerks of very short duration, involving mainly the head and the upper limbs (provoking blinking or head nodding and upward-outward movements of the arms) and, less frequently, the lower limbs. They usually occur several times a day and can vary in intensity from episode to episode. Myoclonus can cause dropping hand-held objects and in the more disabling forms, occasional flexion of the lower limbs with falls to the ground. Reflex MS were elicited in both wakefulness and sleep (predominantly in the two initial stages of N-REM sleep) [
], and different types of provocative stimuli are reported in different types of combination: acoustic, tactile, thermal, proprioceptive, visual triggers and photic stimuli. Somatosensory seizures evoked by touch, reported as light and unexpected, have been described in 27 cases [
Reflex seizures with somatosensory precipitation. Clinical and electroencephalographic patterns and differential diagnosis, with emphasis on reflex myoclonic epilepsy of infancy.
in: Zifkin B.G. Andermann F. Beaumanoir A. Rowan A.J. Reflex epilepsy and reflex seizures: advances in neurology. Lippincott-Raven Publishers,
Philadelphia1998: 193-206
]. In the majority of cases (12 patients), the trigger sites of sensory stimulation, when reported, were the face and/or the head and, less frequently, together with the upper limbs (3 patients), whereas the lower limbs or other body parts are described in 7 patients only (Fig. 1). Only in one case a unilateral sudden, unexpected tapping of the right hand palm elicited seizures [
]. Tactile stimulation associated with other types of stimuli, e.g. acoustic, thermal (such as cool water on the face), proprioceptive or visual stimuli were reported in 32 cases (combination of acoustic and tactile stimuli in 28). Photosensitivity without a clinical correlation is occasionally evident [
] but is not a specific feature of this type of epilepsy. Frequently repeated stimuli do not provoke seizures. It was reported that there is a refractory period lasting between 20 and 30 s and 1–2 min [
]. Furthermore, if children were expecting the stimulus, they had no attack, so startle reaction or an element of surprise, at least initially, appear to be fundamental in triggering attacks. Myoclonic seizures are generally brief and isolated but jerks can also occur in pseudo-rhythmical clusters lasting from 5 to 10 s. Due to the short duration of the seizures it is difficult to assess these young patients’ consciousness, however a little impairment [
] during the myoclonic seizures was reported in 3 patients. Spontaneous attacks were reported frequently, usually occurring after the onset of the reflex seizures and were evident during drowsiness and sleep only [
]. Other types of seizures (e.g. atonic and/or tonic seizures) are not present in RMEI. Neurological evaluation is usually normal, and so are motor and mental development, with no delay or regression in the acquisition of the developmental milestones. All other investigations, such as ophthalmological evaluation, EKG, echocardiogram, abdominal ultrasound scan, brain magnetic resonance imaging, neurometabolic and genetic investigation were unremarkable when performed.
Fig. 1L Delt., left deltoid; L Fem., left femoral; R Delt., right deltoid; R Fem., right femoral; R Scm, right sternocleidomastoid muscle; EKG, electrocardiogram. During sleep: tactile stimulation of the glabella (A) causes a reflex myoclonic seizure related to generalized ictal discharge at the EEG and rhythmic myoclonic jerks recorded on the 2 deltoid muscles and, with minor intensity, on the right sternocleidomastoid muscle and on the 2 femoral quadriceps muscles (bandpass filter, 1.6–30 Hz; notch, 50 Hz; sensitivity, 150 mV/cm). In figure B, tactile stimulation of the right hand causes no response. During wakefulness: biting a breadstick (C) provokes a reflex myoclonic seizure related to generalized ictal discharge at the EEG and rhythmic myoclonic jerks on the different recorded muscles while tactile stimulation of the chin (D) causes no response.
] have described the presence of isolated epileptic abnormalities, brief spike and wave, or polyspikes and wave complexes without electromyographic correlation, during wakefulness and, more often, during sleep. Ictal EEG recordings show isolated or recurrent spikes, polyspike and wave, or generalized spike and wave complexes (at a frequency of 3–4 Hz according to some authors [
]), which are correlated with the myoclonic jerks.
5. Outcome and treatment
RMEI is characterized by better prognosis than MEI, where cognitive outcome is much less certain due to neuropsychological impairment in a third of affected children, treatment duration is longer and the discontinuation of therapy may cause seizure relapse. Furthermore, RMEI shows good response to anticonvulsant drugs, EEG normalization and normal neurological examination at follow-up. Generally, the development of other types of seizures was not reported. The etiological substrate of these epilepsies remains unknown but it is probably similar. For this reason some authors believe that evidence to distinguish two distinct syndromes is insufficient. However, RMEI is probably related to an age-dependent, genetically determined hyperexcitability of the sensorimotor cortex and, in our opinion, brain maturation plays an important role in RMEI resolution.
Some authors do not recommend treatment since myoclonic seizures occur only after a trigger stimulation and are of very brief duration [
Reflex seizures with somatosensory precipitation. Clinical and electroencephalographic patterns and differential diagnosis, with emphasis on reflex myoclonic epilepsy of infancy.
in: Zifkin B.G. Andermann F. Beaumanoir A. Rowan A.J. Reflex epilepsy and reflex seizures: advances in neurology. Lippincott-Raven Publishers,
Philadelphia1998: 193-206
]. Treatment is usually recommended if attacks persist for more than six months. Valproate represents the first-line drug; complete seizure control was rarely achieved by adding either Clonazepam [
Reflex seizures with somatosensory precipitation. Clinical and electroencephalographic patterns and differential diagnosis, with emphasis on reflex myoclonic epilepsy of infancy.
in: Zifkin B.G. Andermann F. Beaumanoir A. Rowan A.J. Reflex epilepsy and reflex seizures: advances in neurology. Lippincott-Raven Publishers,
Philadelphia1998: 193-206
Reflex seizures with somatosensory precipitation. Clinical and electroencephalographic patterns and differential diagnosis, with emphasis on reflex myoclonic epilepsy of infancy.
in: Zifkin B.G. Andermann F. Beaumanoir A. Rowan A.J. Reflex epilepsy and reflex seizures: advances in neurology. Lippincott-Raven Publishers,
Philadelphia1998: 193-206
This clinical entity may be differentiated from other epileptic syndromes, such as startle epilepsy, which may start in childhood but is characterized by poor outcome. The triggering stimuli can involve any sensorial modality (usually auditory stimulus) but they must be sudden and unexpected [
]. Patients usually have large brain lesions, mostly due to perinatal hypoxic brain damage, the seizures can be either partial or generalized and of different types (e.g. myoclonic, tonic), and are often drug-resistant. Other epileptic syndromes with myoclonic seizures in infancy could be confused with tap seizure, e.g. neonatal myoclonic encephalopathy or myoclonic seizures in severe symptomatic epilepsies with neonatal or infantile onset. In these syndromes, seizures may be triggered by sudden somatosensory stimuli. Several other clinical conditions may exhibit reflex myoclonic jerks due to severe neurometabolic or genetic diseases, such as Down Syndrome [
]. All these conditions are usually accompanied by mental developmental arrest or regression, whereas children with RMEI have normal extensive metabolic testing and good outcome. Since an element of surprise is predominant in tap seizure, at least at the onset, differential diagnosis must include early manifestations of startle disease or hyperekplexia, in which excessive startling to an unexpected stimuli (characteristically a tap at the base of the nose, in infants) is associated with tonic contraction and complex movements without epileptic discharges at the EEG. In addition, the outcome is not favourable due to the persistence of excessive jerking, presence of mild developmental delay and of the specific generalized muscular stiffness (Table 2).
Table 2Differential diagnosis. S: spikes; PSW: polyspike and wave; SW: spike and wave.
epileptic disorders
non-epileptic disorder
RMEI
Symptomatic Epilepsy (Lennox-Gastaut, severe myoclonic epilepsy in infancy, etc.)
Startle Disease (Hyperekplexia)
Age at onset
2–24 months
variable
variable (from neonatal period to childhood and puberty)
Trigger
auditory, tactile, visual or thermal stimuli
somatosensory stimuli
sudden stimuli, usually auditory (in infants: tap at the base of the nose)
Non myoclonic epileptic seizures
not reported
multiple seizure types
not reported
Clinical features
normal mental and motor development
mental and/or motor developmental delay
hypertonia appearing in the first months of life
EEG features
INTERICTAL: usually normal background activity.
varies with age and etiology
normal during attacks;
ICTAL: isolated or recurrent S, PSW, SW, generalized complexes
vertex sharp activity may be evoked by sudden noise
Response to treatment
good response when necessary
variable
good response to clonazepam
Outcome
good (seizures disappear, EEG normalization, normal neuropsychological outcome)
depending on underlying condition
excessive jerking persists, mild delay, generalized muscular stiffness, gait disturbance and uncontrolled falls, usually normal mental development
]. The seizures, therefore, could originate from an increase in proprioceptive feedback to the hyperexcitable motor and premotor cortex, and usually display eye blinking and craniocaudal progression, as in a startle reaction. According to this hypothesis, areas activated during sensory stimulations, such as tactile stimuli in different areas of the body (both middle zone of the face, vertex of the head, and unilateral sites like palm of the hand [
]), could overlap or even coincide with regions of cortical hyperexcitability. If this involves a critical mass of cortex and cortico-reticular and cortico-cortical pathways, the final result is a generalized epileptic event [
Tap seizure occurs in children with normal motor and mental neurodevelopment and is characterized by short duration, spontaneous remission, and good prognosis. This condition should be brought to the attention of clinicians because a correct clinical identification would prevent extensive investigations and anticonvulsant drugs, and parents could be reassured as to the absence of long-term neurologic impairment.
Financial disclosure
The authors have no financial relationships relevant to this article to disclose.
Conflicts of interest
The authors have no conflicts of interest to disclose.
References
Ricci S.
Cusmai R.
Fusco L.
Vigevano F.
Reflex myoclonic epilepsy in infancy: a new age-dependent idiopathic epileptic syndrome related to startle reaction.
Revised terminology and concepts for organization of seizures and epilepsies: report of the ILAE Commission on Classification and Terminology, 2005-2009.
Reflex seizures with somatosensory precipitation. Clinical and electroencephalographic patterns and differential diagnosis, with emphasis on reflex myoclonic epilepsy of infancy.
in: Zifkin B.G. Andermann F. Beaumanoir A. Rowan A.J. Reflex epilepsy and reflex seizures: advances in neurology. Lippincott-Raven Publishers,
Philadelphia1998: 193-206
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