Use of the bispectral index (BIS) monitor to aid in the diagnosis of pseudoseizures

Abstract

Editor—Pseudoseizures can be difficult to diagnose, especially in a patient with a history of epilepsy. Generalized tonic-clonic convulsions, followed by a postictal period of drowsiness can appear extremely convincing to even the trained eye. Anti-convulsant medication is often given and a critical care referral may be made if seizures continue. True epileptic seizure activity can only be definitively diagnosed by recording a 2-fold rise in serum prolactin levels from baseline at 20 min post seizure.1Pritchard PB Wannamaker BB Sagel J Daniel CM Serum prolactin and cortisol levels in evaluation of pseudoepileptic seizures.Ann Neurol. 1985; 18: 87-89Crossref PubMed Scopus (78) Google Scholar This may not be feasible in practice, as a baseline level can only be taken after at least an hour of seizure-free activity. An alternative is real-time EEG monitoring by a trained technician, again, for most clinicians, this is not possible. We therefore must rely on clinical acumen. We recently were asked to review a 21-yr-old female, with a history of epilepsy who had presented to our district general hospital 10 h previously with seizures. She had >20 tonic-clonic seizures, lasting 5–10 min since admission to the acute medical assessment unit. Treatment had included lorazepam 4 mg and diazepam 10 mg i.v. She was about to receive a loading dose of phenytoin 15 mg kg−1. Her Glasgow Coma Score (GCS) had been 3 for the previous 2–3 h, and although stable from a cardiorespiratory point of view, the referring physician felt, not unreasonably, that a critical care admission was warranted. It was noted that she had been ventilated twice in the last 6 months in our intensive care unit to aid control of seizure activity. The last note from her neurologist suggested that not all of her seizures could be explained by epilepsy alone. It was noted that her compliance with medication was judged to be poor. We were informed that she had suffered another short seizure some 5 min previously. On examination the GCS was 5, heart rate 90 beats min−1, arterial pressure 116/71 mm Hg and oxygen saturation 99%. She was placed in the recovery position and a size four oropharyngeal airway inserted. Oxygen was continued via reservoir mask. Further observation of the patient saw an effort on her behalf to reposition or partially remove the airway with her tongue. Clinically, we felt that her symptoms and signs did not correlate with true epileptic seizures. Despite encouragement for the patient to open her eyes and respond, she remained in the same state. After deliberation on further management, it was felt that bispectral index (BIS) monitoring (Aspect Medical Systems) might support our clinical diagnosis. After applying electrodes to the forehead immediate readings gave a BIS number in the mid-eighties, and as the signal quality improved the number rose, stabilizing between 92 and 95. With a BIS number in the nineties, we felt this was unlikely to be a postictal state, and hence the seizures may well be pseudoseizures. It was therefore decided, between both teams that the patient would remain on the admissions ward, receive i.v. phenytoin and have no further sedative medication. It was also felt that it was inappropriate to continue with BIS monitoring outside theatres or critical care. Despite further encouragement to open her eyes, she continued in the same state of unresponsiveness. However, 2 h later, after no further seizures, she opened her eyes, asked for a phone and self-discharged contrary to medical advice. Although BIS monitoring does not diagnose pseudoseizure activity, we found it a useful supplement to a clinical diagnosis. The BIS monitor uses an EEG reading from a normal brainwave pattern to derive its number, and its use during a real seizure could not be advised. BIS monitoring during electroconvulsive therapy has been described,2Nishihara F Saito S Pre-Ictal Bispectral Index has a positive correlation with seizure duration during electroconvulsive therapy.Anesth Analg. 2002; 94: 1249-1252Crossref PubMed Scopus (26) Google Scholar and a fall in the BIS number from 54 (±13) post anaesthesia to 30 (±8) in the immediate postictal period was seen. Awakening occurred at a mean BIS number of 45 (±13) (range 29–81). It would therefore seem safe to assume that a BIS reading in the mid-1990s would indicate a state of wakefulness. Pseudoseizures are a psychiatric condition and not neurological, and inappropriate treatment with tracheal intubation increases unnecessarily the risk to the patient.