Discussion
In this case, the patient developed unexplained postoperative DOC, which was suspected to be an epileptic seizure based on the diagnostic and therapeutic intervention. Epilepsy is considered one of the most serious neurological disorders, affecting over 70 million people worldwide [4]. Its incidence follows a bimodal distribution, with the highest risk observed in infants and the elderly. Furthermore, it has been pointed out that approximately 30% of elderly-onset epilepsy cases experience status epilepticus at the time of initial onset, and among them, the frequency of NCSE is high [5]. NCSE is defined as a condition characterized by non-convulsive clinical neurological symptoms caused by EEG seizure activity lasting for more than 30 minutes [6]. The symptoms of NCSE have been reported to manifest as altered consciousness, in the form of confusion or coma, as well as language impairment, myoclonus-like movements, anxiety, excitement, delirium and extrapyramidal symptoms [7]. In this case, the patient initially regained consciousness after completion of general anesthesia. However, shortly thereafter, he experienced loss of consciousness that persisted for more than 30 minutes. Although EEG could not be performed during the episode of impaired consciousness, it is likely that the patient experienced NCSE characterized by the predominant symptom of DOC. NCSE is a condition that is often observed in patients with unexplained DOC in whom no clear cause is identified by imaging. The diagnosis and, hence, treatment of this condition, is often missed because it does not present with obvious seizures. However, if treatment is delayed, it can lead to irreversible brain damage. Therefore, early diagnosis and prompt treatment are crucial [8]. The risk factors for the development of NCSE include prodromal generalized tonic-clonic seizures, a history of epilepsy, advanced age, female gender, and a history of brain injury. Therefore, in the presence of any of these risk factors in a patient with unexplained DOC, NCSE should be considered in the differential diagnosis [9,10]. In this patient, there were no specific risk factors except for advanced age, which made the diagnosis challenging.
The treatment of NCSE often involves the administration of benzodiazepines, which have been found to be effective [11,12]. In this case, significant improvement in consciousness was observed after administration of diazepam. Other medications, such as phenytoin and valproic acid, might also be considered in the treatment. Newer antiepileptic drugs, such as levetiracetam, which have fewer side effects and drug interactions, can also be used for the treatment of NCSE [13].
It is indeed rare to observe the onset of NCSE immediately after the completion of general anesthesia for surgery. To our knowledge, there have been a few reported cases of NCSE occurring after neurosurgical procedures, but only one reported case of NCSE following non-cranial surgery [14]. Our experience suggests that when organic causes for post-anesthetic impaired consciousness are ruled out, NCSE should be considered in the differential diagnosis. If feasible, immediate EEG monitoring should also be considered to aid in diagnosis.
In this case, although a definitive diagnosis of NCSE could not be made due to the unavailability of immediate EEG monitoring, improvement in consciousness level immediately following the administration of diazepam as a diagnostic and therapeutic intervention strongly suggested the possibility of NCSE. Post-anesthetic DOC can often be attributed to residual effects of anesthetic drugs, making it challenging to diagnose NCSE. However, in elderly patients, NCSE should be considered in the differential diagnosis of DOC. Fortunately, in this case, the patient was managed without severe neurological complications.