Morvan syndrome and related disorders associated with CASPR2 antibodies
Jan. 23, 2023
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Transient epileptic amnesia has been considered a syndrome of mesial temporal lobe epilepsy characterized by (1) recurrent episodes of isolated memory impairment of epileptic cause (ictal or postictal) while other cognitive functions remain intact; (2) interictal memory disturbances of accelerated long-term forgetting and autobiographical and topographical amnesia; and (3) late age of onset with a mean of 57 years. The duration of episodes of amnesia is usually less than an hour with usual recurrence of around 20 times each year in untreated patients. In addition, brief seizures typical of mesial temporal lobe epilepsy are detected in two thirds of patients. Interictal EEG, particularly when recorded in sleep, shows temporal lobe spikes whereas EEG during attacks of amnesia demonstrates either ictal discharges or postictal features. In most cases of transient epileptic amnesia, no clear cause for the epilepsy is identified though MRI may show hippocampal atrophy or focal structural lesions in the temporal lobes. Transient epileptic amnesia is considered rare though it is frequently underdiagnosed or misdiagnosed as transient global or psychogenic amnesia. Patients with transient epileptic amnesia usually have an excellent prognosis; seizures respond extremely well to monotherapy with small doses of lamotrigine or levetiracetam though interictal memory disturbances may persist.
• Transient epileptic amnesia has been considered a syndrome of mesial temporal lobe epilepsy with recurrent episodes of amnesia (ictal or postictal).
• The duration of episodes of amnesia is usually less than an hour (median duration 30 to 60 minutes).
• The attacks are frequent, usually around 20 times each year in untreated patients.
• Two third of patients also present with brief seizures of mesial temporal lobe epilepsy.
• Documentation of the epileptic nature of transient epileptic amnesia requires meticulous clinical assessment and EEG.
• Transient epileptic amnesia usually affects middle-aged or elderly subjects, men (60%) more than women, and the attacks often occurring on waking.
• Interictal memory manifestations consist of accelerated long-term forgetting as well as autobiographical and topographical amnesia.
• Monotherapy with lamotrigine or levetiracetam is effective in controlling the seizures and the amnestic attacks in the majority of patients, but interictal memory disturbances may persist.
The earliest description of epilepsy-related transient amnesia is attributed to the case of Dr. Z detailed by Hughlings Jackson in 2 reports (22; 23; 12). Dr. Z had from the age of 21 years attacks typical of temporal lobe epilepsy with secondarily GTCS and severe postictal amnesia caused by a single, circumscribed lesion in the left uncus discovered at autopsy after his death from chloral overdose:
In the remainder of this article I shall speak only of Z’s slight seizures. I witnessed but two of them… In one he stopped talking to me, remained standing, and made slight, very slight, just audible (vide supra) smacking movements of his lips. … On another occasion he was sitting in a room consulting me; he stopped talking--I have no remembrance of any smacking movements of his mouth on this occasion--his head was bent forward, but in a second or two, the paroxysm being then, I suppose, over, he looked up, and next (postparoxysmal stage of actions) he leaned over one arm of his chair and felt about on the floor as if searching for something. Next he did the like on the other side……
Soon, perhaps a minute, afterwards, his actions, or I should say the irrelevant-seeming actions, ceased; he replied correctly to simple questions and told me that it was not necessary for me to go home with him. He, however, looked confused and seemed strange. When we got to his house a few yards away, I thought he was fully recovered, and, as I was thinking of making another room on the ground floor of my house, I took the opportunity of speaking to him about a third room on the ground floor of his house. Among other things he said he used to breakfast there. I was surprised when he afterwards, next day, told me that he remembered nothing from the time of being in my room consulting me (before the fit) to a little time after I left him at his own house (23).
This case with postictal amnesia is unlikely to be considered part of the syndrome of transient epileptic amnesia because of the early age at onset. In subsequent reports, it has been well documented that transient amnesia:
(A) occurs as an ictal or postictal symptom in association with temporal lobe epilepsy and
(B) is sometimes the only manifestation or the only seizure type of temporal lobe seizures in some patients (55; 53).
It has also been reported that seizures causing prominent amnesia are easily mistaken for episodes of transient global amnesia or of psychogenic amnesia, and various terms have been used to describe these attacks, including pure amnestic seizures, ictal amnesia, epileptic amnesia, epileptic amnesic attacks, epileptic transient amnesia, and transient epileptic amnesia (55; 53; 11).
The term “transient epileptic amnesia” was introduced by Narinder Kapur, who highlighted that amnesic attacks caused by epilepsy are similar to the syndrome of transient global amnesia, but they may have certain distinguishing features, including brevity and recurrence, which appeared to stand out as supportive of a diagnosis of transient epileptic amnesia and as rather atypical for transient global amnesia (24).
A significant advance in our current understanding of transient epileptic amnesia has been made thanks to the United Kingdom-wide "TIME" (The Impairment of Memory in Epilepsy) project. More information about this project can be accessed at:The Impairment of Memory in Epilepsy (TIME) Project (24; 09; 08; 07; 33; 35; 54).
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