Diagnostic features of functional/ dissociative seizures in the first presentation of transient loss of consciousness.

Objectives: Previous studies have identified features in patient's history and seizure descriptions supporting a clinical diagnosis of functional / dissociative seizures (FDS). However, most studies involved patients with chronic seizure disorders. This study explores the value of reported features for a clinical diagnosis of FDS in an adult population with a first presentation of transient loss of consciousness (TLoC).

Methods: We prospectively recruited patients newly presenting with TLoC to an Emergency Department (ED), Acute Medical Unit (AMU; admitting ward for general medical patients), first seizure or syncope clinic. We invited participants to complete an online questionnaire, either at home or at time of initial assessment. Two expert raters determined cause of participants' TLOC after 6-month follow-up. We also reviewed clinical records at this timepoint to extract relevant information for assessment of putative diagnostic features (13 categorical variables and 6 interval or continuous variables), and validation of two previously-developed diagnostic classifiers.

Results: We included 178 patients in final analysis (134 syncope, 32 epilepsy, 12 FDS). 3 categorical variables were significantly more common in FDS: fluctuating course or waxing/waning movements (p = 0.0037), asynchronous limb movements (p = 0.0024), and preserved ictal awareness or responsiveness (p = 0.0013). Three interval/continuous variables supported diagnosis of FDS: younger age at onset (area under receiver-operating characteristic curve [AUC] = 0.865 (0.771-0.960)); total non-ictal symptoms reported on structured review of systems (AUC = 0.834 (0.730-0.928)); and total peri-ictal symptoms self-reported on structured questionnaire (AUC = 0.864 (0.781-0.948)).

Conclusions: Our study does not find support for some clinical features previously reported as diagnostic of FDS in adult patients with a first presentation of TLoC. Features suggestive of preserved ictal responsiveness (reported by witnesses) and awareness (in the form of total number of self-reported peri-ictal symptoms) support FDS diagnoses.