Altered mental status differential diagnosis

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Pratik Bahekar, MBBS [2]


Differential Diagnosis

A lowered level of consciousness indicate a deficit in brain function. Level of consciousness can be lowered when the brain receives insufficient oxygen (as occurs in hypoxia); insufficient blood (as occurs in shock); or has an alteration in the brain's chemistry.[1] Metabolic disorders such as diabetes mellitus and uremia can alter consciousness. Hypo- or hypernatremia (decreased and elevated levels of sodium, respectively) as well as dehydration can also produce an altered LOC.[2] A pH outside of the range the brain can tolerate will also alter LOC.[3] Exposure to drugs (e.g. alcohol) or toxins may also lower LOC,[1] as may a core temperature that is too high or too low (hyperthermia or hypothermia). Increases in intracranial pressure (the pressure within the skull) can also cause altered LOC. It can result from traumatic brain injury such as concussion. Stroke and intracranial hemorrhage are other causes. Infections of the central nervous system may also be associated with decreased LOC; for example, an altered LOC is the most common symptom of encephalitis.[4] Neoplasms within the intracranial cavity can also affect consciousness, as can epilepsy and post-seizure states.[3] A decreased LOC can also result from a combination of factors. A concussion, which is a mild traumatic brain injury (MTBI) may result in decreased LOC.

Other Illnesses That Can Mimic Delirium, Stupor, and Coma

In patients with altered mental status, the emergency physician must also consider other neurologic diagnoses. In patients who appear unresponsive, locked-in syndrome should be considered and is caused by focal injury to the ventral pons secondary to an infarct, hemorrhage, or trauma. If secondary to an infarct, the distal basilar artery is usually occluded. Multiple sclerosis and central pontine myelinosis can also cause locked-in syndrome. Though the clinical presentation is variable, quadriplegia and anarthria is usually present, but vertical eye gaze and upper eyelid movement are usually retained. Despite having the outward appearance of being unresponsive, patients with locked-in syndrome have normal levels of consciousness and are fully aware of their surroundings. If locked-in syndrome is suspected, then prompt neuroimaging and neurology consultation are warranted. Patients with a suspected thromboembolic cause of locked-in syndrome should immediately go to interventional radiology for intra-arterial thrombolytic therapy, even if the symptoms have being ongoing for more than the traditional 3-hour window. Without emergent intervention, survival and neurological recovery for these patients can be poor.

Non-convulsive status epilepticus (NCSE) should also be considered in patients who have altered mental status, especially if no obvious cause for their mental status changes is found. This diagnosis should strongly be considered if the patient has a seizure history or had a seizure prior to arriving to the ED. One systematic review reported that NCSE occurred in 8% – 30% of patients with altered mental status (mean prevalence = 22%). This systematic review consisted of 5 studies that predominantly enrolled patients in the hospital setting. NCSE is an underrecognized and important form of altered mental status that can only be diagnosed with electroencephalography (EEG). If this cause of altered mental status is considered, then neurology consultation should be obtained promptly; the treatment of NSCE (benzodiazepine and anti-epileptic medications) is significantly different from other causes of altered mental status.


  1. 1.0 1.1 Pollak AN, Gupton CL (2002). Emergency Care and Transportation of the Sick and Injured. Boston: Jones and Bartlett. p. 140. ISBN 0-7637-1666-9. Retrieved 2008-07-04.
  2. Johnson AF, Jacobson BH (1998). Medical Speech-language Pathology: A Practitioner's Guide. Stuttgart: Thieme. p. 142. ISBN 0-86577-688-1. Retrieved 2008-07-04.
  3. 3.0 3.1 Tindall SC (1990). "Level of consciousness". In Walker HK, Hall WD, Hurst JW. Clinical Methods: The History, Physical, and Laboratory Examinations. Butterworth Publishers. Retrieved 2008-07-04.
  4. Scheld WM, Whitley RJ, Marra CM (2004). Infections of the Central Nervous System. Hagerstown, MD: Lippincott Williams & Wilkins. p. 219. ISBN 0-7817-4327-3. Retrieved 2008-07-04.