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1647,48,49. The underlying pathophysiological mechanism is thought to be a sodium
channelopathy because the condition is highly responsive to carbamazepine and there is
possibly some overlap with afebrile infantile convulsions and channelopathy-related
epilepsies, such as autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE).

Episodic ataxias typically present in childhood or adolescence and manifest as ataxia and
myokymia (type 1, potassium channelopathy) or vertigo, ataxia and occasionally syncope
(type 2, calcium channelopathy). These events are commonly diagnosed as epilepsy and EEG
recordings can show sharp and slow waves. Moreover, true epileptic seizures can occur,
confounding the diagnosis further.

Painful tonic spasms of multiple sclerosis and other upper motor neuron disorders are
involuntary, unilateral dystonic movements that are frequently precipitated by movement.
The clinical history and neurological examination should usually provide sufficient evidence
to differentiate between tonic spasms of, for example, multiple sclerosis, epileptic seizures
and paroxysmal dyskinesias.

Startle syndromes are a heterogeneous group of disorders, comprising hyperekplexia, startle
epilepsy and neuropsychiatric syndromes, which are characterised by an abnormal motor
response to startling events. Despite some clinical overlap, a carefully recorded history is
frequently sufficient to accurately differentiate these entities50. Hyperekplexia is
characterised by an exaggerated startle response consisting of forced closure of the eyes and
an extension of the extremities followed by a generalised stiffness and collapse. It can be
mistaken for cataplexy in patients with narcolepsy, or atonic or tonic epileptic seizures. More
minor forms of hyperekplexia display an exaggerated startle response without tonicity and
collapse. Hyperekplexia may be hereditary, due to a genetic mutation in the alpha-1 subunit
of the glycine receptor on chromosome 5, sporadic or symptomatic, secondary to widespread
cerebral or brainstem damage. Clonazepam may be helpful in reducing both the severity of
the startle response and degree of tonicity51.

Startle epilepsy usually manifests as an asymmetric tonic seizure, triggered by a sudden
stimulus52,53. Other ictal patterns such as absences, atonic seizures, or generalised seizures are
less common. EEG abnormalities during such seizures may be obscured by profuse
electromyographic activity in the pericranial muscles, although occasionally epileptiform
activity over the vertex may be seen. Startle-provoked seizures usually become manifest after
spontaneous epileptic seizures of the same ictal phenotype have been present for a prolonged
period with a high-frequency, possibly due to a kindling-like phenomenon. In the majority of
cases, both ictal phenotype and neuroimaging data suggest a seizure onset zone within the
supplementary motor area. Other than hyperekplexia, startle-induced conditions which may
be confused with reflex startle epilepsy include stiff-person syndrome54 and progressive
encephalomyelitis with rigidity and tetanus, although the presence and nature of concomitant
neurological symptoms and signs readily distinguish these conditions from each other.

Transient focal sensory attacks

Migraine and epilepsy are both characterised by paroxysmal cerebral dysfunction and a
possible relationship between migraine and epilepsy has been postulated55,56. Migraine is
frequently mistaken for epilepsy, particularly in acephalgic migraine, when the headache is
mild or absent. Epileptic seizures can be accompanied or followed by migraine-like
headache57-59, and attacks of migraine can lead to unconsciousness60, particularly in basilar
migraine61, and acute confusion62,63. Migraine attacks can cause epileptiform EEG
abnormalities64-66, although the EEG changes are usually non-specific. It has been suggested
that episodes of migraine with aura may provoke seizures, in a condition termed
‘migralepsy’67, although this has not been universally accepted68.