Encephalopathy and delirium commonly have infectious or metabolic etiologies. May also be drug-induced (focus of this SMQ). In the case of metabolic disorders, it is possible that drug plays a contributory or causative role for underlying metabolic abnormality. Encephalopathy and delirium may be reported synonymously; however delirium may be narrower in scope. 1) Encephalopathy: Defined as any degenerative or diffuse disease of the brain that alters brain structure or function. Many sub-forms including: biliary; demyelinating; Wernicke's; secondary to infections; and secondary to drug-induced metabolic disorders such as hepatic encephalopathy, hyperammonemia, hypoglycemia, hyponatremia, uremia. Leukoencephalopathy (encephalopathy with white matter lesions) may be secondary to drug-induced hypertension. Hallmark is altered mental state. Other symptoms include lethargy, fluctuation of level of consciousness, nystagmus, tremor, dementia, seizures, myoclonus, and muscle weakness. Cerebral edema is common. 2) Delirium (Acute confusional state): Delirium is a clinical state characterized by fluctuating disturbances in cognition, mood, attention, arousal, and self-awareness. May be due to primary brain diseases or secondary to other diseases. Causes include: metabolic; toxic (drugs); structural (vascular occlusion and cerebral infarction); intracerebral hemorrhage; primary or metastatic brain tumors; and infections. Signs and symptoms include clouding of consciousness with disorientation, changes in personality and mood, delusions, hallucinations (commonly visual), paranoia, withdrawal, agitation, disordered speech.