Nonconvulsive status epilepticus: master of disguise.

Abstract

To the Editor: Nonconvulsive status epilepticus (NCSE) is an epileptic state in which there is some impairment of consciousness associated with ongoing seizure activity according to electroencephalography (EEG). Clinically it may be disguised as altered mental status. Antiepileptic drugs are the mainstay of seizure treatment, although they can sometimes paradoxically induce seizure when they are in the toxic range. We report a case of an 81-year-old woman who presented with altered mental status who was found to have NCSE with mildly supratherapeutic phenytoin level. An 81-year-old woman from an assisted living facility presented with acute change in mental status. She had had an episode of confusion lasting a few minutes, with eyes rolled backward but no loss of consciousness. She had no memory of the event. The staff member present did not witness tonic-clonic seizure, tongue biting, or bowel or urinary incontinence. Her past medical history included mild cognitive impairment and epileptic disorder diagnosed at the age of 30, consisting of generalized tonic-clonic seizure associated with urinary incontinence, the last episode of which had been 5 months before admission. She was taking phenytoin and levetiracetam at the time of admission. On admission, her mental status returned to baseline. Initial laboratory tests, including comprehensive metabolic panel, liver function test, septic screen, and brain imaging, were normal. Her phenytoin level was supratherapeutic at 24.2. During her hospitalization, she was disoriented and had difficulty following complex commands and answering questions. Out of concern about seizure, EEG was performed, revealing severely abnormal waveform characterized by disorganization, epileptiform discharges, and excessive slowing consistent with NCSE. She was loaded with sodium valproate immediately, with gradual improvement of her mental status. Her phenytoin dosage was reduced to avoid paradoxical seizure induced by phenytoin toxicity. Repeat EEG 24 hours later demonstrated improvement in waveforms. She was discharged shortly after with weaning regimen of phenytoin. The prevalence of epilepsy increases with age, doubling from the sixth to eighth decade. The clinical presentations of epilepsy may be challenging to differentiate from delirium in elderly adults, which affects approximately 14% to 56% of all hospitalized older people. Confusion may be the manifestation of ongoing seizure or postictal manifestation, resulting from transient brain dysfunction after seizure. Nonconvulsive status epilepticus is an epileptic state in which there is some impairment of consciousness associated with ongoing seizure activity on EEG.1, 2 Classic cases of NCSE probably account for approximately 5% to 20% of all cases with status epilepticus. Diagnosis of NCSE is a challenge given the absence of motor manifestation. It can have protean symptoms associated with an alteration of mentation, which are often missed.3 NCSE may lead to neuronal injury and cytotoxic edema, which is caused by an abrupt increase in blood pressure and subsequent cerebral vasoconstriction leading to cerebral ischemia.4, 5 In a retrospective study, EEG was performed in 56% of 177 elderly adults who presented to the emergency department with delirium; 84% of which were abnormal, with three revealing NCSE. These people had longer hospital stays and a rate of higher institutionalization. The study recommended that EEG be performed in all older adults with delirium,6 but given limited resources, urgent EEG may not be available, especially after office hours. Another study demonstrated that the presence of remote risk factors for seizures and eye movement abnormalities, as in the woman described above, has a sensitivity of 100% for NCSE, and EEG should be ordered urgently.7 Paradoxical intoxication has been described with most antiepileptic drugs (AEDs), including phenytoin, leading to confusion and, rarely, seizures.8 The level required to cause seizures has been reported to be much higher than 20 μg/dL. An increase in frequency of focal seizures secondary to phenytoin is due to anticonvulsant activity at the neuronal membrane.9 Seizures during intoxication are rare with monotherapy but with polytherapy, the therapeutic range of AEDs may change and can exert seizure-inducing action or at least loss of their usual efficacy in suppressing seizure.10 Therefore, reduction of dosage of AEDs often decreases seizure frequency. In conclusion, geriatricians and internists should have a high index of suspicion of NCSE in individuals with epilepsy presenting with acute altered mental status, despite normal or supratherapeutic phenytoin levels, especially in individuals taking more than one AED. An urgent EEG should be the next step of investigation. Early recognition and treatment may shorten length of stay and improve outcomes in these individuals. Conflict of Interest: The editor in chief has reviewed the conflict of interest checklist provided by the authors and has determined that the authors have no financial or any other kind of personal conflicts with this paper. Author Contributions: Tan E.K.: data analysis, developed image, literature review, writing manuscript. Loh K.P.: manuscript revision, critical review of manuscript for important intellectual content. Sponsor's Role: No sponsor.