Brain involvement in various diseases produces encephalopathy, or a confusional state, which clinically presents with acute or subacute cognitive and alertness alterations. There are different types of encephalopathies that can have metabolic, electrolyte, endocrine, infectious, inflammatory, or autoimmune origins. Most EEG recordings in these cases are nonspecific, indicating the existence of a cerebral disorder but not differentiating between subtypes. Very few types, however, present specific tracings (herpesvirus encephalitis, subacute sclerosing panencephalitis, autoimmune encephalitis, or Creutzfeldt-Jakob disease). There are common and probably differential numerical characteristics between the subtypes of encephalopathies, which could aid in an etiological diagnosis. As an example, the difference between COVID-19, toxic-metabolic, and hypoxic encephalopathy is shown.