With regard to parietal lobe disease, the term anosognosia, using “anos,” disease, is used to describe a group of disorders in which there is an unawareness of a deficit. While used most frequently to describe a lack of recognition, neglect, or indifference to a left sided paralysis or even to ownership of the limb, the term anosognosia is appropriate to denote the inability to perceive a number of deficits based on cerebral disease including blindness, hemianopia, deafness, and memory loss. Anosognosia is usually associated with a number of additional abnormalities. Often there is a blunted emotionality. The patient is inattentive and apathetic, and shows varying degrees of general confusion. There may be an indifference to performance failure, a feeling that something is missing, visual and tactile illusions when sensing the paralyzed part, hallucinations of movement, and allochiria (one-sided stimuli are felt on the other side).
The patient may act as if nothing is wrong. If asked to raise the paralyzed arm, he may raise the intact one or do nothing at all. If asked whether the paralyzed arm has been moved, the patient may say “yes.” If the fact that the arm has not been moved is pointed out, the patient may admit that the arm is slightly weak. If told it is paralyzed, the patient may deny that this is so or offer an excuse: “My shoulder hurts.” If asked why the paralysis went unnoticed, the response may be, “I’m not a doctor.” Some patients report that they feel as though their left side had disappeared, and when shown the paralyzed arm, they deny it is theirs and assert that it belongs to someone else or even take hold of it and fling it aside. The mildest form of anosognosia is reflected by an imperfect and reduced appreciation of the degree of weakness. On the other extreme of the conceptual negation of paralysis are instances of self-mutilation of the paralyzed limb (apotemnophilia). It should be pointed out that the loss of body schema and the lack of appreciation of a left hemiplegia are separable, some patients displaying only one feature.
The lesion responsible for the various forms of one-sided anosognosia lies in the cortex and white matter of the superior parietal lobule. Rarely, a deep lesion of the ventrolateral thalamus and the juxtaposed white matter of the parietal lobe will produce a similar contralateral neglect. Unilateral asomatognosia is many times more frequent with right (nondominant) parietal lesions as with left-sided ones (seven times more often according to Hécaen). The apparent infrequency of right-sided agnosic symptoms with left parietal lesions is attributable in part, but not entirely, to their obscuration by an associated aphasia.
Another common group of parietal symptoms consists of neglect of one side of the body in dressing and grooming, recognition only on the intact side of bilaterally and simultaneously presented stimuli (sensory extinction) as mentioned above, deviation of head and eyes to the side of the lesion (transient), and torsion of the body in the same direction. The patient may fail to shave one side of the face, apply lipstick, or comb the hair only on one side.
Unilateral spatial neglect is brought out by having the patient bisect a line, draw a daisy or a clock, or name all the objects in the room. Homonymous hemianopia and varying degrees of hemiparesis may or may not be present and interfere with the interpretation of the lack of application on the left side of the drawing.