EEG clues to misdiagnosed epilepsies


By Mardi Chapman

12 Jun 2019

Differentiation of epileptic seizures from dissociative attacks remains challenging without the benefit of video EEG (VEEG), according to a Brisbane study.

 The study, presented at the 2019 American Academy of Neurology Annual Meeting in May, comprised a case review of all patients seen at the Mater Advanced Epilepsy Unit between 2015 and 2018.

Two cohorts of patients had a diagnostic reclassification following VEEG review of their cases including 16 patients initially diagnosed with dissociative attacks and subsequently re-diagnosed with epilepsy.

The meeting was told semiology commonly consisted of non-naturalistic, complex motor or hypermotor movements. The most common networks implicated in an incorrect diagnosis were pre-frontal especially the insulo-cingulate network and the mesial parietal networks.

A second cohort of 46 patients were initially diagnosed with epilepsy and then re-classified as dissociative attacks following VEEG.

The semiology varied widely from somatosensory descriptions to hypotonia to generalised convulsions.

Dr Fiona Chan, an advanced trainee in neurology, told the limbic the differentiating element was that dissociative attacks were not associated with an ictal discharge on EEG.

“Hence, the gold standard for a dissociative attack diagnosis is the absence of ictal changes on VEEG during an attack. Differentiating events based on prior descriptions alone can be very difficult and reasons behind an incorrect initial diagnosis can be related to patients not accessing centres with VEEG capabilities and epileptologist assessment, which can be limited in certain regions.”

However in a small number of patients, misinterpretation of EEG recordings occurred when there was a lack of correlation with the seizure semiology.

Dr Chan said the more common event of patients with dissociative attacks being misdiagnosed as epilepsy led to most patients being prescribed antiepileptic drugs with the attendant risk of adverse effects.

“This is exacerbated as the events continue or worsen,” she said. “The drugs will typically be increased and additional agents added resulting in polypharmacy, issues with toxicity and drug – drug interactions.”

“As with any condition, a patient who is refractory to therapy should have the diagnosis revisited.”

In patients with epilepsy who were misdiagnosed as dissociative attacks, delay in appropriate treatment and seizure control runs the risk of higher morbidity and mortality.

“Ultimately, patients in either cohort who are misdiagnosed are delayed in receiving effective treatment which results in a lack of symptom control that impedes upon daily optimal function including ability to work or drive and severely impacts their quality of life with negative psychosocial consequences.”

“We advocate for a thorough analysis of the seizure semiology based on a good understanding of neuroanatomical networks in combination with interpretation of neurophysiological findings on EEG. In short, anatomoelectroclinical correlation is essential to accurate diagnosis.”

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