Out of Africa: observations on the histopathology of Mycobacterium ulcerans infection.

Abstract

Introduction Mycobacterium ulcerans infection produces progressive skin ulceration in man and other mammals. The disease was first described in 1948 in patients from the Bairnsdale district in Australia' but was known in Africa well before this time.2 It has since been recorded in many, mostly tropical countries in Africa, Central and South America, and South East Asia.3 The infection characteristically occurs in defined areas which are associated with river or lacustrine systems draining tropical or warm-temperature rain forest. Like the flora to which it is related, the mycobacterium shows a Gondwanian distribution which is evidence of its great antiquity.4 The disease usually begins as a skin papule (stage IA) which later ulcerates (stage 2) (fig 1)5; less commonly the infection may first appear as a subcutaneous nodule (stage 1B)6 which subsequently affects the dermis and then ulcerates, or sometimes the disease may produce diffuse oedema of a limb (stage 1 C),7 due to a necrotising panniculitis, which clinically mimicks cellulitis. The infection is usually on extremity but, particularly in children, it may affect the face or trunk.8 Occasionally, the necrotic process extends through deep fascia with involvement of muscle9 and even bone.'0 Metastatic infection may occur. The features of the pathology ofM ulcerans infection have been described'; additional characteristics of the disease, as observed in Zaire (Belgian Congo), have been detailed in the papers by Janssens et al.7 l Infection in Uganda has been described by Dodge,'2 13 and later by Connor and Lunn,'4 15 and infection in Papua New Guinea by Lytton and Lavett. 6 Hayman and McQueen described the pathology in additional Bairnsdale district patients in 1985.1' Burchard and Bierther'8 briefly described the pathology of the disease as seen in Gabon; their paper was illustrated with electron photomicrographs of M ulcerans. The earlier descriptions of the pathology of the disease have been comprehensively reviewed. '9 In the original paper' MacCallum detailed the clinical and macroscopic appearances of the ulcers with straight or undermined edges, subcutaneous spread producing nodules of induration and eventual ulceration at a distance from the initial lesion (fig 1), and the development in the subcutaneous tissue of an abundant gelatinous mass like blubbery granulation tissue which could be readily wiped off with gauze. Histologically, necrotic tissue lined the ulcer wall and floor and extensive necrosis of fatty tissue extended beneath the Figure 1 Clinical appearances of Mycobacterium ulcerans infection, on the posterolateral aspect of the left leg in a 64 year old man. The photograph demonstrates the undermining of skin and the development of a satellite lesion associated with extensive necrosis of subcutaneous fat. (Photograph, courtesy ofMr Kendall Francis, FRACS.).