astereognosis

Astereognosis is a neurological condition characterized by the inability to recognize objects by touch despite intact somatic sensation. It is a form of tactile agnosia resulting from damage to the brain’s somatosensory processing networks, most often in the contralateral parietal lobe, particularly the somatosensory association cortex in the posterior parietal region. Primary somatosensation may be preserved, so simple tactile discrimination and proprioception can remain intact.

Clinical features include the inability to identify familiar objects placed in the hand with vision occluded, even though the person can feel weight, texture, and shape. Patients often rely on vision to identify objects and may have coexisting parietal lobe signs such as neglect or apraxia.

Testing is typically performed with the patient blindfolded or otherwise unable to see the object. A familiar object is placed in the hand, and the patient is asked to name or describe it. Testing is performed for both hands. Additional bedside assessments, such as graphesthesia and two-point discrimination, may be used to characterize the broader somatosensory deficit.

Causes are most commonly strokes affecting the parietal cortex or its connections (especially the superior parietal lobule and posterior parietal regions), but can also include tumors, traumatic brain injury, or demyelinating disease. Astereognosis may occur with other parietal lobe syndromes and neglect.

Management focuses on treating the underlying lesion and rehabilitating sensory function, often through occupational therapy and sensory re-education. Patients may rely on visual strategies to compensate, and prognosis depends on lesion extent and neuroplastic recovery.