subject: Cutaneous tuberculosis [print this page] Cutaneous tuberculosis Cutaneous tuberculosis
Involvement of the skin by Mycobacterium tuberculosis isrelatively uncommon in developed countries but is oftenseen in the developing world, where the overall prevalenceof tuberculosis is much higher. The condition still needs tobe considered in the west, particularly in those who havemigrated from the Indian subcontinent and Africa. Manydescriptive terms have been applied to the wide variety ofclinical presentations that can occur, and to some extentthese reflect the mode by which the skin may be affected:haematogenous spread from a deep source (most lupusvulgaris); direct spread from underlying organs, e.g. lymphnodes, bones, respiratory or gastrointestinal tract (scrofuloderma,tuberculosis cutis orificialis); direct inoculationfrom outside (some lupus vulgaris, tuberculosis verrucosacutis and warty TB).The commonest form is lupus vulgaris, which presents asan area of indurated, reddish-brown skin, characteristicallyon the head and neck, although lesions mayoccur elsewhere. The lesions gradually spread and have atendency to produce scar tissue, which results in distortionof normal anatomy and loss of hair follicles in hair-bearingareas. When the microorganism is inoculated directly intothe skin, lesions sometimes have a warty surface.Tuberculosis may result in a number of skin changesin which the microorganisms are not directly involved(known as tuberculides}: Erythema nodosum , in which the lesionsusually appear in association with primary infection; Erythema induratum (or Bazin's disease), in which thenodular, ulcerative lesions appear on the lower legs,involving the calves as well as the shins;The rare papulonecrotic and lichenoid forms.Investigation of suspected cutaneous tuberculosis involvesbiopsies for histology and culture and a search for involvementof internal organs.
Atypical mycobacterial infections The skin may become infected by direct inoculation ofother mycobacteria, especially Mycobacterium marinum,an organism responsible for a systemic infection in fish. Anindurated nodule or nodules appear, usually on the handor arm of a fish-fancier. In some patients, furthernodules appear along the lines of lymphatic drainage (socalledsporotrichoid spread). Occasionally lesions may bemore widespread, especially in those who catch the organism from swimming. Biopsy for histology and culture should be performed, but the tissue must be incubated onspecial media at low temperature for the organism to grow.Lesions often resolve spontaneously, but this is a slowprocess and therefore treatment with antibiotics may beindicated. Various drugs have their advocates: minocycline,co-trimoxazole and rifampicin are all considered to beeffective. Treatment should be for about 6 weeks.
