The goal of the mental status examination is to determine if an abnormality of mental status exists and whether it points to a structural, metabolic, toxic, or infectious etiology.
An alteration of mental status requires a deficit in alertness or awareness or both. Alertness requires the normal functioning of the ascending reticular activating system (ARAS), which passes through the midline of the brainstem up through the thalamus, resulting in arousal of the cerebral hemispheres. Awareness, tested as orientation, requires alertness plus the normal functioning of the cerebral hemispheres. The obtunded patient responds to voices, but there is an abnormality in alertness. Because the ARAS passes through the pontine tegmentum in proximity to the medial longitudinal fasciculus, one needs to examine for focal brainstem deficits, especially pupillary or gaze abnormalities, in the obtunded patient. The drowsy patient may have a decreased level of alertness or awareness, so that one needs to examine for cortical and brainstem deficits. The alert patient may have deficits in awareness but no brainstem lesions that affect the ascending reticular activating system. Deficits in awareness point to abnormalities in cortical function. Questions to assess awareness center on orientation to time, place, person, and situation, as well as the ability to follow simple commands. Determining the digit span (normally seven numbers forward and five numbers backwards) can provide a quick assessment of the mental ability impaired in dementia. Confusion of right and left and the inability to calculate (subtracting 7 serially from 100 or 3 serially from 20) are abnormalities resulting from a dominant parietal lobe lesion. Having the patient recall three objects after a five-minute interval assesses recent memory.
Reversible causes of altered mental status such as hypoglycemia, narcotic overdose, hypoxia, or hypercarbia should be quickly investigated and treated. If a structural etiology of altered mental status is indicated by history or associated neurologic findings, a noncontrast head CT or possibly other neuroimaging study is needed emergently.
Delirium is a distinctly abnormal mental state characterized by disorientation, fear, irritability, misperception of sensory stimuli, and, often, visual hallucinations. Delirium accompanies diffuse metabolic and multifocal cerebral illness, and its presence implies a generalized impairment of brain functions or at least a bilateral involvement of limbic structure. In the elderly patient presenting with delirium from a nursing facility, a diagnosis of high frequency is urosepsis.
Psychiatric causes of altered mental status produce abnormalities of affect, behavior, and content of consciousness, but not of alertness and awareness. In psychosis, there is a defect in reality testing, so that hallucinations and delusions are accepted many times as real. Psychiatry uses organic brain syndrome to denote a dementia, which is an impairment of awareness due to various pathological lesions usually scattered throughout the cerebral hemispheres.
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