Uncommon Infections: Mycobacterium TB

Mycobacterium TB

This has many cutaneous manifestations. It is usually imported to UK but HIV is an important risk factor. It is estimated that one-third of the world’s population is infected with TB (though mostly without apparent disease). Indian subcontinent and sub-Saharan Africa highest prevalence. The diagnosis should be suspected in unusual lesions in patients from endemic areas. The disease pattern is determined by degree of immunity.

Lupus vulgaris classical type of cutaneous TB which affects individuals with good immunity. Due to direct inoculation or more commonly lymphatic/haematogenous spread from an underlying focus. Usually affects otherwise normal skin especially head/neck/face. Initially painless red-brown plaque with apple jelly appearance on diascopy slowly enlarges & progressively destructive. May be a plaque, a nodule or ulcerated. Regional lymphadenopathy may be present. Histology is granulomatous with acid fast bacilli (AFB). Mycobacterial culture is positive in 6% of cases caused by direct inoculation into non-immune subjects.

Lupus Vulgaris - granulomatous plaque

Warty tuberculosis - presents as re-infection in a previously sensitised patients often from the Far East with good immunity due to direct inoculation of hands/feet/knees warty nodule or plaque. The differential diagnosis is a deep fungal infection.

Scrofuloderma - breakdown of skin overlying focus of infection usually over cervical lymph node resulting in a bluish red nodule or ulcer with fistulae. Haematogenous spread. The patient is usually unwell with multiple bluish papules, vesicles or pustules. Skin biopsy shows the presence of AFBs.

Scrofuloderma – note the scarring and lymphadenopathy

Tuberculides - cutaneous response to internal TB in young person with good immunity. Probably bacilli within lesions (on PCR) but not cultured. Internal TB may not be apparent. Papulonecrotic tuberculide is characterised by recurrent symmetrical crops of non-itchy necrotising papules that heal with scarring and can continue for months. The differential diagnosis is pityriasis lichenoides acuta. Erythema induratum presents with crops of small tender nodules on the distal lower legs, usually the calves. It is seen in patients with TB, usually pulmonary disease or tuberculous cervical lymphadenitis. Treatment is with standard anti-TB therapy. Response to treatment supports diagnosis, especially with tuberculides.