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Studies of the semiology of DS have focused on motor phenomena and the features of
epilepsy lacking in DS. Little attention has been paid to subjective symptoms that might be
regarded as the psychiatric phenomenology of DS78,79. Patients with DS commonly report a
feeling of being cut off at the onset of their seizure and describe a number of symptoms of
autonomic arousal. These include tachycardia, perspiration, hyperventilation, peripheral
paraesthesia, carpopedal spasm and a dry mouth. Patients may not volunteer these symptoms
and sometimes a history of hyperventilation will only emerge from an eyewitness account.
Such symptoms are reported by approximately 60% of DS patients, compared with around
30% of patients with partial seizures66.

Other features on history which support (and only that) a diagnosis of DS include an absence
of risk factors for epilepsy, a failed response to AEDs and the presence of risk factors for DS
(see below). Here again there are pitfalls. Patients with DS commonly report a significant
past neurological history22 as well as a family history of epilepsy23.

It used to be supposed that the majority of patients with DS also suffered from epilepsy. As
studies have become more sophisticated, however, estimates of the prevalence of comorbid
epilepsy have become ever smaller. Probably no more than 15 or 20% of patients with DS
also have epileptic seizures3,16,18,24. A history of multiple (dissociative) seizure types is given
by 20% of patients with DS16,18.

Psychiatric comorbidity
Studies of psychiatric diagnoses in patients with DS have reported a broad range of
prevalence figures. High rates of depression, anxiety disorder, personality disorder and post-
traumatic disorder have been reported16. Often the presence of such a history will raise
suspicion of DS, but high rates of psychiatric disorder are also seen in association with
epilepsy, at least in those patients with intractable epileptic seizures, and may not help
distinguish the two disorders25-27. A history of previous medically unexplained symptoms is
very common in DS and an important pointer to the diagnosis16.

Ictal observation/examination
An opportunity to observe a seizure may provide invaluable information. Whether the patient
is responsive to verbal requests should be established. Careful note should be taken of the
type and distribution of movements and whether apparent clonic movements are rhythmic
and synchronous (as they usually are in epilepsy) or not (DS). Following a generalised tonic-
clonic seizure the corneal reflex will usually be absent and plantar responses extensor. Pupils
will be unresponsive to light in organic states of impaired consciousness. If the patient’s eyes
are shut the examiner should attempt to open them noting any resistance (DS). A simple test
to look for avoidance of a noxious stimulus is to hold the patient’s hand over their face and
drop it: in DS the patient may be seen to control their arm movement so their hand falls to
one side. If the eyes are open, evidence of visual fixation may be sought in two ways. The
first involves rolling the patient onto their side. In patients with DS the eyes will often be
deviated to the ground. If this is the case, the patient should be rolled onto the other side to
see if the eyes are still directed towards the ground (the ‘Henry and Woodruff sign’)31. A
second useful manoeuvre is to hold a small mirror in front of the patient and look for evidence
of convergent gaze and fixation on the reflection. This procedure will often stop the seizure.
Patients with factitious disorder may learn to produce the ‘correct’ response in all of these
examination procedures.

Investigations

EEG
Unfortunately the EEG still contributes to diagnostic errors in this group of patients. Non-
specific EEG abnormalities are found in up to 15% of healthy individuals and all too often