Altered mental status (AMS) is a general term used to describe various disorders of mental functioning ranging from slight confusion to coma. Given the vagueness of the term, it is imperative to understand its key components before considering a differential diagnosis. Fundamentally, mental status is a combination of the patient's level of consciousness (i.e., attentiveness) and cognition (i.e., mental processes or thoughts); patients may have disorders of one or both. For example, patients with meningitis may have impaired consciousness (i.e., altered sensorium, decreased attentiveness) with intact cognition, whereas patients with dementia may have a normal level of consciousness with impaired cognition. However, more frequently, patients exhibit altered levels of consciousness plus cognition: for example, with delirium, a relatively common and sometimes fatal cause of AMS.
An observational study conducted in the accident and emergency department found that an acutely AMS was the primary reason for the visit for about 1% of all adult patients and 2.4% of older adults. About 40% of patients were aged over 60 years. Thirty-five percent of cases had a neurological cause (e.g., stroke, traumatic brain injury, or seizures). Acute alcohol intoxication, infection, and metabolic abnormalities were other common causes of AMS.
Another observational study reported that over half of adults aged over 65 years with AMS had delirium. Mortality was almost 25%, and the mortality rate increased if AMS lasted longer than 3 days. In this group, infection and neurological disease were the most common aetiologies.
Levels of consciousness
Normal state of consciousness consists of either the state of attentiveness in which most people function while not asleep, or one of the recognised stages of normal sleep from which the person can be easily aroused. Abnormal state of consciousness is more difficult to categorise, and many terms are used. Some of the more common terms include:
Hyper-alert: heightened arousal with increased sensitivity to immediate surroundings. Hyper-alert patients can be verbally and physically threatening, restless, and/or aggressive.
Confused: disorientated; bewildered, and having difficulty following commands.
Delirious: disorientated; restless, hallucinating, sometimes delusional.
Somnolent: sleepy, responding to stimuli only with incoherent mumbles or disorganised movements.
Lethargic: reduced level of alertness with decreased interest in the surrounding environment.
Obtunded: similar to lethargy; the patient has a lessened interest in the environment, has slowed responses to stimulation, and tends to sleep more than normal, with drowsiness in between sleep states.
Stuporous: profoundly reduced alertness and requiring continuous noxious stimuli for arousal.
Comatose: state of deep, unarousable, sustained unconsciousness.
- Stroke and transient ischaemic attack
- Head injury
- Seizures with possible postictal state
- Myocardial infarction
- Congestive heart failure
- Ventricular arrhythmias
- Dehydration (volume depletion)
- Hepatic encephalopathy
- Acute systemic infection
- Bipolar disorder
- Acute psychosis
- Alcohol withdrawal
- Alcohol toxicity
- Drug toxicity
- Drug withdrawal
- Hip fracture
- Pulmonary embolism
- Subdural haematoma
- Epidural haematoma
- Subarachnoid haemorrhage
- Brain tumour
- Non-convulsive status epilepticus
- Hypertensive encephalopathy
- Wernicke's encephalopathy (thiamine deficiency)
- Carbon monoxide poisoning
- Adrenal insufficiency
- Myxoedema coma
- Pituitary apoplexy
- Brain abscess
- Mesenteric ischaemia
- Acute diverticulitis
Assistant Professor of Medicine
University of Massachusetts Medical School
GB declares that he has no competing interests.
Dr Gary Blanchard would like to gratefully acknowledge Dr David Dosa, a previous contributor to this topic.
Assistant Clinical Professor of Medicine
Division of Neurology
Duke University Medical Center
TC has worked as a paid speaker for GlaxoSmithKline and Pfizer in 2008 and 2009.
Consultant in Old Age Psychiatry
Mental Health Unit
KA declares that he has no competing interests.
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