Agraphesthesia
Definition and Clinical Testing
Agraphesthesia (also known as dysgraphesthesia or graphanesthesia) is the inability to recognize letters or numbers traced on the skin, typically on the palm of the hand. It is a disorder of higher-order tactile sensation, requiring both intact primary sensation (touch) and cortical processing to interpret the shape.
To test for graphesthesia, the examiner asks the patient to close their eyes and then uses a dull object, like a key or a pen cap, to trace a single number or letter onto the patient's palm. An inability to identify the character correctly suggests the presence of agraphesthesia.
Graphesthesia is tested by tracing a number or letter on the patient's palm while their eyes are closed.
Anatomical Basis and Clinical Significance
Agraphesthesia is a valuable clinical sign that points to a lesion in the contralateral somatosensory cortex of the parietal lobe. The parietal lobe is responsible for integrating sensory information, including touch, pressure, and spatial awareness, which are all necessary for this task.
There is some debate as to whether agraphesthesia is a primary perceptual deficit or a form of tactile agnosia (sometimes termed "agraphognosia"). Regardless of the precise classification, its presence is a reliable indicator of parietal lobe dysfunction.
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