The mechanism of the neural signs and symptoms of leprosy.

The clinical signs of leprosy include, besides other things, hypopigmentation, anidrosis, keratosis, depilation and anesthesia in patches of skin, or anesthesia and trophic changes in extremities apart from skin lesions. All these signs are generally ascribed to the degeneration of nerves. There is no doubt that degenerative changes do take place in the peripheral nerves and their branches, and that many of the clinical signs of leprosy are produced as a result of those changes. However, I find difficulty in explaining all the manifestations mentioned on the basis of nerve degeneration alone. As early as 1930 I noticed that sensation might return suddenly in an anesthetic skin area when it became red and thick under "reaction."l Conversely, it was noticed that when nonanesthetic, erythematous, thickened patches subsided they sometimes became anesthetic. Since then several other anomalous conditions have been observed that cannot be explained satisfactorily on the basis of nerve degeneration alone. For one thing there is often seen marked disproportion between the clinical signs in a patch and the obvious involvement of the associated nerves, and also disproportions between the different signs themselves. For example, there may be little or no sensory change in a patch with gross thickening of the associated nerve, or marked sensory change may be found in a patch with little or no nerve thickening. Moreover, the degrees of anesthesia, hypopigmentation, and other changes in a patch may vary considerably. If all these changes were due to the degeneration of the nerves, how can we explain the wide variations seen? Similar disproportion between the nerve trunk involvement and the signs produced may be found in polyneuritic cases: (a) A considerable