Astereognosis is the inability to discriminate between objects of differnt shapes, textures, weights, and size based on touch alone. It can be caused either by damage to sensory nerve pathways or, where there is little or no sensory loss, by lesions in the parietal lobe of the brain. Where there is parietal lobe damage the asterognosis will be on the opposite (contralateral) side of the body to the lesion.

Astereognosis is tested by asking the patient to close his/her eyes and then placing familiar objects such as a key or coin in his/her hand and asking him/her to identify it.

A similar condition also caused by lesions to the sensory pathways or the parietal lobe is agraphesthesia. This is the inability to recognise letters or numbers drawn on the patient's hand with a semi-sharp object.

Stereognosis links:
The Complete Neurological Examination
Neurological History and Physical Examination

MS Glossary
All About Multiple Sclerosis