Rare and unusual ... or are they? Less commonly diagnosed encephalopathies associated with systemic disease.

Encephalopathy due to hepatic or renal failure, electrolyte disturbances, or the administration of benzodiazepines and narcotics is commonly encountered, well reviewed in the literature, and, therefore, not usually missed. This article focuses on encephalopathies that were previously well described but may be overlooked by modern clinicians, as well as those that are still taught in the classroom but seldom thought of in practice. Due to the presumed relative rarity of these cases and emphasis on the well-memorized "classic" clinical presentations, these often treatable, and perhaps not so rare, encephalopathies due to systemic medical illness may go undiagnosed and untreated. Pancreatic encephalopathy, Wernicke's encephalopathy, and pellagra encephalopathy are reviewed in detail; cefepime and ifosfamide encephalopathies are discussed as examples of specific medication-induced encephalopathies. Septic encephalopathy, central pontine myelinolysis, and fat embolism syndrome are briefly reviewed. The encephalopathies reviewed have the potential for devastating neurological consequences if recognition and, therefore, treatment are delayed. Clinical improvement for many of these syndromes depends on prompt intervention. This article highlights some representative examples of less-commonly diagnosed metabolic and toxic encephalopathies.