Effect of Mycobacterium leprae in peripheral nerve trunk on the evolution of skin lesions

Comparative histological studies were made of a) 41 peripheral nerve lesions and the skin in the area of supply, and b) 12 peripheral nerve lesions and concurrent but unrelated skin lesions. In the first study, small, relatively early, histologically classifiable skin lesions were found in all cases, even though there were no clinical lesions. In every case the lesion was centered on a dermal nerve. In some cases disruption of the perineurium was associated with emergence of the lesion into the dermis and a small silent local reaction. It was concluded that there was a descending spread of the disease down the neural pathway to the dermis, although it was not necessarily associated with transport of bacilli. Although the first study showed a discrepancy in the classification between skin and nerve lesions in nearly 50% of the cases (as previously reported), the second study showed no discrepancies. It is suggested that discrepancies are relatively uncommon, and that those in the first study are exceptional. The probable explanation is that microreactions in the nerve trunks had caused a shift in classification, which was not yet reflected in the immature skin lesions. In the second study, the mature skin lesions had reached immunological equilibrium. Discrepancies in classification between skin and nerve lesions, as between concurrent skin lesions, are the result of reaction. Attention is drawn to the probable role of subliminal reactions in the evolution of infections.