For the ability to sense a sharp object, the best screening test uses a safety pin or other sharp object to lightly prick the face, torso, and 4 limbs; the patient is asked whether the pinprick feels the same on both sides and whether the sensation is dull or sharp. The sharp object is discarded after use to avoid potential transmission of bloodborne disorders eg, HIV infection, hepatitis.
Cortical sensory function is evaluated by asking the patient to identify a familiar object eg, coin, key placed in the palm of the hand stereognosis and numbers written on the palm graphesthesia and to distinguish between 1 and 2 simultaneous, closely placed pinpricks on the fingertips 2-point discrimination.
Another indicator of impaired cortical sensory function is extinction, which is inability to identify a stimulus on one sideโone that can be identified when one side of the body is tested at a timeโwhen both sides of the body are tested simultaneously. For example, when extinction is present, patients report feeling sensation on only one side when simultaneously touched on both sides even though they can feel sensation on both sides when one side is tested at a time.
If the patient cannot identify these tiny movements with eyes closed, larger up-and-down movements are tried before testing the next most proximal joints eg, testing the ankles if toe movement is not perceived. Pseudoathetosis refers to involuntary writhing, snakelike movements of a limb that result from severe loss of position sense; motor pathways, including those of the basal ganglia, are preserved.
Typically, when the eyes are closed, the patient cannot locate the limb in space. Inability to stand with feet together and eyes closed Romberg test indicates impaired position sense in the lower extremities. When cerebellar disease is present, the patient tries to stand with the feet apart but as close together as possible without falling and only then closes the eyes. Rarely, a positive result is due to severe bilateral loss of vestibular function eg, aminoglycoside toxicity.
