The diagnosis of leprosy - common errors
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Would the correct diagnosis of leprosy have been easier if this disease had been described in textbooks on Neurology instead of Dermatology? The emphasis on the changes in the skin of the patient with leprosy may well be the cause of misdiagnosis in many cases. Leprosy is a chronic infective disease and it is generally accepted to be caused by Mycobacterium Leprae discovered by Dr. A. Hansen in 1873 and published by him in 1874. M. Leprae is an acid-alcohol fast bacillus. So far no artificial medium has been found in which to culture the bacillus, but it can be kept alive and will multiply in the earholes and foot pads of the mouse and hamster. The foot pads are used solely as a culture medium enabling the testing of the effect of drugs on the bacillus. It is important to know that M. Leprae has a special affinity for the Schwann cells of the sensory nerves in which they lie, protected by the basement membrane, (only seen by electron microscopy) and if conditions are suitable multiply. Only nerves of the Peripheral Nervous system are affected in leprosy. Therefore without symptoms showing nerve involvement the diagnosis of leprosy should not be made in the absence of positive skin smears. The great auricular nerve-the ulner and median and peroneal nerves are easy to palpate and possess predominantly cutaneous sensory fibres. In the early stages of the disease the bacillary invasion is directed to the sensory fibres while later on all types of fibres are affected due to granulomatous infiltration, scarring, ischaemic damage or even possibly tramsneuronal spread. Autonomic nerve fibres are commonly involved early in the disease, shown by the characteristic dryness and roughness of the skin and anhydrosis. This article is mainly written for doctors who have never worked in countries where leprosy is prevalent and therefore have some difficulty in recognising the disease. To be Leprosy-conscious is as important and essential as to be Malaria-conscious and this applies to patients of all races. Leprosy can occur in ALL races and at any age. It should bc born in mind that Europeans are not exempt from leprosy and unfortunately it has happened that Europeans have been treated for many years for an unidentified skin disease which later proved to be leprosy.
- Ministry of Health