Improvement in cutaneous sensibility associated with relief of pain.

It is often found that when there is a lesion in the peripheral or the central nervous system causing pain or local tenderness, stimuli applied to the skin of the affected part are not clearly perceived. The clarity of touches with von Frey hairs or cottonwool, the discreteness of pinpricks, the definite perception of when a stimulus is applied and when removedthese may all be absent. Evidence will be presented here showing that when the state of tenderness or pain is removed, such features of the perception of stimulation may be improved, and that this improvement occurs even when a large number of peripheral nerve fibres from the part are put out of action. In fact we may have a condition in which a reduction in the number of conducting nerve fibres results in an improvement in the sensibility of the part. In the most definite examples, there is a diminution in actual sensibility associated with a subjective improvement in perception. The material illustrating this relation between local pain and cutaneous sensibility is now presented, grouped in the following manner. The first case shows how the local pain and tenderness could be relieved in many ways, and on all occasions where relief occurred there was improvement in subjective sensibility of the part. The second case shows how blocking a peripheral nerve on two occasions may cause a lasting improvement in the quality of the sensibility of the affected part. There follows a group of four cases in which intrathecal injections of phenol in "myodil" or glycerol relieved pain due to cancer; this has been associated with subjective improvement in sensibility. The final group consists of experiments on normal subjects, and it shows how very light stimuli to the skin can be more clearly felt just before nerve conduction fails, this being brought about by occluding the circulation to the limb.