Pain sensory testing evaluates the presence of a lesion affecting the peripheral nerve, lateral spinothalamic tract, thalamus or sensory cortex.
Use a hygienic device capable of providing a sharp sensation but not capable of breaking the skin, and something to produce a contrastingly blunt sensation. Demonstrate the two stimuli, then ask the patient to close their eyes. Apply randomly sharp and blunt stimuli to the skin, asking the patient to identify each.
General neurological screening would include random proximal and distal test locations; diagnostic investigation would involve dermatomal mapping and/or peripheral nerve distribution testing.
A positive finding involves the inability to identify sharp stimuli within a certain area of skin. This should be carefully mapped in order to assist identification of relevant peripheral nerve or nerve root distribution. Sensory deficit may result from an ipsilateral lesion in the peripheral nerve or at the relevant spinal segmental level, or a contralateral lesion above that level in the CNS
Factors affecting discrimination include skin thickness, and force and consistency of applied pressure. Consider other neurological test results including temperature sensation, which also involves the lateral spinothalamic tracts.