Clinical Pearls & Morning Reports
Cutaneous involvement is relatively uncommon in Mycobacterium tuberculosis infection. Patients with cutaneous tuberculosis can present with a variety of clinical findings, which can be classified according to the method by which mycobacteria are disseminated to the skin. Read the latest Case Records of the Massachusetts General Hospital here.
Q: Does cutaneous tuberculosis always develop from an endogenous source of infection?
A: Direct inoculation of mycobacteria from an exogenous source into a host can be manifested by tuberculous chancre or tuberculosis verrucosa cutis. These cutaneous manifestations are localized to the site of inoculation.
Q: What are some of the other manifestations of cutaneous tuberculosis?
A: Spread of mycobacteria from an endogenous source may result in scrofuloderma, a suppurative nodular process that often develops on the skin overlying affected lymph nodes and then drains, leading to sinus formation and resultant cordlike scars. Hematogenous spread of mycobacteria, known as miliary tuberculosis, may have cutaneous manifestations, such as a generalized, monomorphic papular, pustular, or nodular process. Lupus vulgaris is a chronic, scarring, and deforming process that may occur either as a direct result of an underlying focus of M. tuberculosis infection or after hematogenous or lymphatic spread of infection. The eruption associated with lupus vulgaris classically affects the central portion of the face and can progress slowly over a long period of time.
A: The other category of cutaneous tuberculosis is tuberculids, skin eruptions that are thought to occur in reaction to an underlying, often occult, focus of M. tuberculosis infection. There are three main types of tuberculids: erythema induratum, lichen scrofulosorum, and papulonecrotic tuberculid. Erythema induratum appears as red-to-violaceous nodules or plaques on the posterior calf and is localized. Lichen scrofulosorum appears as many discrete, often monomorphic, 2-to-4-mm, flat-topped papules, usually on the trunk. Papulonecrotic tuberculid is usually a symmetric, recurring eruption of 2-to-8-mm, firm, inflammatory papules that can turn into pustules and become necrotic over time, scarring over a period of weeks. If papulonecrotic tuberculid goes untreated, it may persist for years.
A: Confirming the diagnosis of papulonecrotic tuberculid is challenging. Tuberculids are commonly considered to be hypersensitivity eruptions, and in patients with these disorders, acid-fast stains of smears or histopathological sections of skin-biopsy specimens would not normally be expected to identify mycobacteria, although it is possible. Similarly, mycobacterial cultures of skin-biopsy specimens are unlikely to be positive, although the tuberculid reaction can be seeded by the hematogenous spread of mycobacteria and organisms can be isolated from these lesions in some cases.