Abstracts

Rationale: Patients with altered mental status not otherwise specified (AMS NOS) are frequently referred for routine (20-40 minute) electroencephalogram (EEG). The intention is to rule out seizures specifically non-convulsive seizures (NCS) as the etiology of AMS. The EEG may also suggest a structural or metabolic/ toxic cause of AMS and thus helps guide further diagnostic work up. The aim of our study was to determine the diagnostic utility of the EEG to clarify and differentiate possible causes of altered mental status. Methods: All consecutive routine/portable EEGs of adult inpatients (= or > 18 years of age) with the diagnosis of AMS, change in mental status or encephalopathy over a nine-month period (July 2009 - March 2010) were reviewed by a board certified electroencephalographer and clinical neurophysiology fellows. EEGs were reviewed for 1. Slowing -focal vs. diffuse, 2. Presence or absence of epileptiform features (sharp waves or spike wave discharges), 3. Special features- triphasic waves, periodic lateralized epileptiform discharges (PLEDS), generalized periodic epileptiform discharges (GPEDS) and bilateral independent periodic epileptiform discharges (BIPLEDS). In addition, we correlated the neuroimaging findings in patients with focal abnormalities on EEG. EEG records of patients who underwent long-term video EEG monitoring were reviewed to determine whether it aided further diagnostic assessment and plan. Results: A total of 122 EEG studies with a diagnosis of AMS were referred to the lab during the above nine month time period. Overall, there were 15 (12.3 %) normal EEGs and 107 (87.7%) abnormal EEGs. Among the abnormal EEGs, 94 (87.8%) showed slowing. Diffuse slowing occurred in 70/94 (74.5%) while focal slowing occurred in 24/94 (25.5%). Epileptiform discharges were seen in 13 (10.6%) of all EEGs reviewed, of which 12 (92.4%) had focal epileptiform discharges. No definite seizures were recorded in any of the EEGs reviewed. Triphasic waves were present in 22 (18%) of all EEGs reviewed. PLEDS were seen in 2 EEGs while none had GPEDS or BIPLEDS. Among the patients who had focal slowing on EEG, 18 out of 24 (75%) had a concordant abnormality documented on neuroimaging. Among the patients who had focal epileptiform abnormalities on EEG, only 5 out of 12 (41.7%) had a corresponding abnormality on neuroimaging. 10 patients underwent further prolonged video-EEG monitoring. Video EEG monitoring suggested the possibility of nonconvulsive status epilepticus in one patient of these 10 patients. Conclusions: Routine/portable EEG studies are useful in the diagnostic workup of patients with altered mental status. The majority of EEGs of patients with altered mental status showed slowing. Triphasic waves, epileptiform discharges, and PLEDs were seen in a minority of the EEGs. EEG has a high sensitivity but low specificity in elucidating the etiology of AMS.