Tuberculosis and tuberculids

Published on 19/03/2015 by admin

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Tuberculosis and tuberculids

Yasaman Mansouri and John Berth-Jones

Evidence Levels:  A Double-blind study  B Clinical trial ≥ 20 subjects  C Clinical trial < 20 subjects  D Series ≥ 5 subjects  E Anecdotal case reports

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Cutaneous manifestations of infection with Mycobacterium tuberculosis are varied and are influenced considerably by the immune status of the patient. Cutaneous tuberculosis (TB) is often misdiagnosed due to its diverse clinical features and the difficulty demonstrating acid-fast bacilli on histology specimens. Cutaneous inoculation with M. tuberculosis can occur from an endogenous source, via lymphatic, hematogenous or contiguous spread, and causes periorificial TB, lupus vulgaris (LV), scrofuloderma, acute miliary TB, and tuberculous gumma. LV can also result from primary inoculation of the skin from an exogenous source, although this usually leads to tuberculous chancre and tuberculosis verrucosa cutis (warty TB). The tuberculids are ‘hypersensitivity’ reactions to extracutaneous sources of M. tuberculosis (tuberculous antigen) in individuals with high levels of immunity. Skin biopsy specimens from tuberculids seldom reveal mycobacteria histologically, although more sensitive PCR techniques do sometimes detect mycobacterial antigens. The tuberculids include erythema induratum of Bazin, erythema nodosum, lichen scrofulosorum, papulonecrotic tuberculid, and nodular tuberculid. Tuberculids respond to treatment of the underlying tuberculosis.

Management strategy

Clinical examination, typical histological findings and the presence of M. tuberculosis in tissue culture remains the gold standard method for diagnosis of TB. Early diagnosis is essential, to prevent further spread of disease.

Newer tests have overtaken the tuberculin skin tests (TST), which can show false positive results in individuals with previous bacille Calmette–Guérin (BCG) vaccination, as well as those infected with M. avium, and be falsely negative in the presence of immunosuppression. Interferon-γ release assays (IGRA) such as T-SPOT assay TB test (T-SPOT), and QuantiFERON-TB Gold test (QTF-G) have high specificity for identification of M. tuberculosis infection and require only one patient visit.

Identification of acid-fast bacilli in tissue cultures often fails as cutaneous TB cases are often paucibacillary. Polymerase chain reaction (PCR) is being used more frequently because of its high sensitivity and specificity.

Once cutaneous TB has been diagnosed, it is imperative to search for an extracutaneous focus of infection. Contact tracing is an important component of efficient TB management. HIV testing is recommended in all patients with diagnosed or suspected TB.

The aims of treatment are to rapidly cure the patient, to reduce transmission of TB to others, and to prevent the development and transmission of drug resistance. The standard treatment regimens recommended are based on controlled trials carried out for pulmonary tuberculosis. The standard 6-month regimen for adults comprises rifampicin (10 mg/kg), isoniazid (INH) (5 mg/kg), pyrazinamide (35 mg/kg), and ethambutol (15 mg/kg) for the initial 2 months of ‘intensive phase treatment’, followed by rifampicin and INH for a further 4 months in the ‘continuation phase’, ideally in fixed-dose combinations. Daily dosing throughout treatment is preferred. Occasionally longer treatment regimens may be necessary to achieve a complete cure, such as in HIV positive cases. Multidrug-resistant tuberculosis should be managed at specialist centers.