Anosognosia refers to a patient’s unawareness or denial of illness. The term was first used by von Monakow (1885) and has been used to describe denial of blindness (Anton’s syndrome), deafness, hemiplegia (Babinski), hemianopia, aphasia, and amnesia. Some authorities would question whether this unawareness is a true agnosia, or rather a defect of higher level cognitive integration (i.e., perception).
Anosognosia with hemiplegia most commonly follows right hemisphere injury (parietal and temporal lobes) and may be associated with left hemineglect and left-sided hemianopia; it is also described with right thalamic and basal ganglia lesions. Many patients with posterior aphasia (Wernicke type) are unaware that their output is incomprehensible or jargon, possibly through a failure to monitor their own output. Cerebrovascular disease is the most common pathology associated with anosognosia, although it may also occur with neurodegenerative disease, for example the cognitive anosognosia in some patients with Alzheimer’s disease.
The neuropsychological mechanisms of anosognosia are unclear: the hypothesis that it might be accounted for by personal neglect (asomatognosia), which is also more frequently observed after right hemisphere lesions, would seem to have been disproved experimentally by studies using selective hemisphere anesthesia in which the two may be dissociated, a dissociation which may also be observed clinically. In Alzheimer’s disease, anosognosia may be related to memory dysfunction and executive dysfunction.
At a practical level, anosognosia may lead to profound difficulties with neurorehabilitation. Temporary resolution of anosognosia has been reported following vestibular stimulation (e.g., with caloric testing).
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 Neuropsychology1989; 11: 143-205
Morris RG, Hannesdottir K. Loss of "awareness" in Alzheimer’s disease. In: Morris RG, Becker JT (eds.). Cognitive neuropsychology ofAlzheimer’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.