Anosognosia

Definition and Historical Context

Anosognosia refers to a patient’s profound unawareness or outright denial of a neurological or medical illness. The term was first introduced by von Monakow in 1885 and has since been used to describe the denial of various profound deficits, including blindness (Anton’s syndrome), deafness, hemiplegia (famously described by Babinski), hemianopia, aphasia, and amnesia. Some authorities debate whether this unawareness is a true agnosia (a primary perceptual defect) or rather a higher-level defect of cognitive integration and self-monitoring.

Clinical Presentations and Syndromes

Anosognosia manifests uniquely depending on the underlying deficit being denied:

• Anosognosia for Hemiplegia: Patients may vigorously deny that their paralyzed limb is weak, sometimes contriving elaborate excuses for why they cannot move it, or even claiming the limb belongs to someone else (somatoparaphrenia).
• Anosognosia for Aphasia: Many patients with posterior aphasia (Wernicke's type) are entirely unaware that their speech output is incomprehensible or jargon. This likely arises from a failure to monitor their own auditory output.
• Cognitive Anosognosia: Commonly seen in neurodegenerative diseases like Alzheimer’s disease, where patients lack insight into their own progressive memory loss and cognitive decline.

Pathophysiology and Neuroanatomy

Anosognosia with hemiplegia most commonly follows right hemisphere injury (specifically the parietal and temporal lobes) and may be strongly associated with left hemineglect and left-sided hemianopia. It is also described with right thalamic and basal ganglia lesions. Cerebrovascular disease is the most common pathology associated with acute anosognosia.

The exact neuropsychological mechanisms of anosognosia remain unclear. The hypothesis that it might simply be accounted for by personal neglect (asomatognosia)—which is also more frequently observed after right hemisphere lesions—has been largely disproved experimentally. Studies using selective hemisphere anesthesia (the Wada test) have shown that the two conditions can be dissociated, a dissociation that is also observed clinically. In Alzheimer’s disease, anosognosia appears to be related to a combination of severe memory dysfunction and executive dysfunction.

Clinical Impact and Management

At a practical level, anosognosia leads to profound difficulties with neurorehabilitation. Patients lacking insight into their impairments are often unmotivated to participate in therapy and are at high risk for falls and injuries due to ignoring safety precautions. Interestingly, temporary resolution of anosognosia for hemiplegia has been reported following vestibular stimulation (e.g., with caloric testing using cold water irrigation of the ear), which transiently modulates spatial awareness networks in the right hemisphere.

 

References

Adair JC, Schwartz RL, Barrett AM. Anosognosia. In: Heilman KM, Valenstein E (eds.). Clinical neuropsychology (4th edition). Oxford: OUP, 2003: 185-214

Celesia GG, Brigell MG, Vaphiades MS. Hemianopic anosognosia. Neurology 1997; 49: 88-97

McGlynn S, Schacter DL. Unawareness of deficits in neuropsychological syndromes. Journal of Clinical and Experimental Neuropsychology 1989; 11: 143-205

Morris RG, Hannesdottir K. Loss of "awareness" in Alzheimer’s disease. In: Morris RG, Becker JT (eds.). Cognitive neuropsychology of Alzheimer’s disease (2nd edition). Oxford: OUP, 2004: 275-296

Starkstein SE, Fedorof JP, Price TR, Leiguarda R, Robinson RG. Anosognosia in patients with cerebrovascular lesions: a study of causative factors. Stroke 1992; 23: 1446-1453.

 

Cross References

Agnosia; Anosodiaphoria; Asomatognosia; Cortical blindness; Extinction; Jargon aphasia; Misoplegia; Neglect; Somatoparaphrenia