Mixed-type encephalopathies: preliminary considerations.

This preliminary report deals with a polyetiological and pathophysiologically multifacted encephalopathy that is fairly common and yet in need of identification as a clinical (but not nosological) entity: Mixed-Type Encephalopathy (MTE). MTE is a mostly acute condition, characterized by change of mentation (confusion, delirium, etc.) with little or no neurological deficit but with impressive diffuse EEG slowing. A variety of medical conditions lead to MTE, especially at an age above 50 years, but status-post-surgery (leaving aside cranial neurosurgery, but also cardiac surgery in view of common embolic cerebral pathology) may also result in MTE, especially with the use of general anesthesia. An attempt is made to analyze the plethora of contributory factors and underlying pathophysiological mechanisms. All types of classical brain pathology such as strokes, meningitis-encephalitis and typical metabolic encephalopathies (hepatic, renal, etc.) and others must be excluded from the diagnosis of MTE. Special emphasis is being placed on behavioral and EEG criteria in the early state of impaired consciousness with subdivision into 4 types: obtundation, somnolence, morbid lethargy and delirium. Cases of MTE are best picked up by an interdepartmental consultation (liaison) service making use of neurological consultations and EEG assessment. The value of the latter cannot be overestimated in these cases, especially in view of the very limited contributions of neuroimaging methods. The prognosis tends to be good. Severe and fatal developments are usually due to intervening cerebral hypoxia or anoxia. In such a development, epileptic manifestations, which are usually absent or mild in MTE, can become quite prominent. A thorough multi-institutional and international study of MTE is already in the planning stage. It is hoped that preventive measures can minimize the cerebral complications.