2.2.12 Skin Tuberculosis and Atypical Mycobacterioses (MOTT)

1B12.8

Skin Koch disease, Lupus vulgaris, Tuberculosis cutis, MOTT (Mycobacteria other than tuberculosis).

Tuberculosis (TB) is a world-wide frequent infection with around 10 million new cases each year. It affects frequently the lungs, the mediastinal or peripheral lymph nodes, urogenital tract, bone, nervous system or the skin. Immune suppression is a risk factor of developing tuberculosis (malnutrition, AIDS). This disease occurs more frequently in developing countries.

Atypical mycobacterial skin infections include fish tank (or swimming pool) granuloma caused by Mycobacterium marinum (typically papulonodules or ulcers of the hands/limbs), Buruli ulcer caused by Mycobacterium ulcerans (cutaneous nodule or ulcer), present in tropical countries, and infections with M. chelonae, M. abscessus,  or M. fortuitum, present worldwide, and most frequently found after skin injections, tattoos, skin trauma or surgery. 

Skin infection with Mycobacterium tuberculosis and MOTT complex.

Classical tuberculosis by Mycobacterium tuberculosis is transmitted by droplets. Infectious droplets are generated when persons with pulmonary or laryngeal TB disease cough, sneeze, shout or sing. MOTT of the lungs may be transmitted via droplets ( M. avium or kansasii ) or on the skin by contact with defective skin barrier.

Cutaneous tuberculosis can appear in different forms depending on immune status. Lupus vulgaris:  red-brown papules with apple-jelly color on glass diascopy. Tuberculosis cutis verrucosa or prosector´s warts: verrucous plaque-like lesions. Tuberculids: erythema induratum of Bazin, lichen scrofulosorum and papulonecrotic tuberculids. Erythema induratum of Bazin presents typically as inflammatory nodules of the limbs in elderly women.

Lupus vulgaris and tuberculids can appear anywhere on the body. Tuberculosis cutis verrucosa is frequently found on the hands or face. Erythema induratum of Bazin presents on lower limbs, specific localisation in Mycobacterium marinum at hands and lower arms.

Skin tuberculosis results from direct inoculation or systemic spread of Mycobacterium tuberculosis complex. Cutaneous atypical mycobacterial infection are non-tuberculous mycobacterial infections of the skin, excluding leprosy.

Mantoux-test: local inoculation with tuberculin toxin. After two or three days, the diameter of the induration is measured and is used to define positivity. A positive test indicates a previous contact with the Mycobacterium tuberculosis complex.

Quantiferon-TB-Gold-test (interferon-gamma release assay) is another indirect, highly sensitive and specific laboratory test that detects the presence of a cellular immune response against M. tuberculosis.

Bacterial culture (Lowenstein medium) has a slow growth. From biopsies PCR tests can be used to prove the presence of different types of mycobacteria.

Faster discrimination follows by PCR from biopsy.

Tuberculosis: granulomatous infiltrate with caseating necrosis. Bacilli are colored by Ziehl-Neelsen, Fite Faraco and by immunohistochemistry staining.

Tuberculosis is a chronic disease and if untreated, the infection can spread to other organs.

Ulcerations, scaring, mutilations or systemic spread, squamous cell carcinoma on chronic skin ulcers.

Detection of the different types of mycobacteria by Ziehl-Neelsen and immunohistochemistry  staining, PCR or mycobacterial direct examination and culture, associated with a consistent clinical context.

Early lupus vulgaris may mimic psoriasis vulgaris or discoid lupus erythematosus. MOTT can mimic different skin infections such as ulcers, deep impetigo, nodular vasculitis and leprosy.

Treatment of TB is becoming more complicated today because of high worldwide distribution of resistance. It typically relies on isoniazid, rifampicin for six months, together with ethambutol and pyrazinamide in the first two months. Bacterial culture has to be initiated prior to treatment to evaluate resistance.

Treatment of MOTT is different to classical tuberculosis and is based on antibiotics such as  tetracyclines, fluoroquinolones, macrolides (eg, amikacin, clarithromycin), rifampicin and sulfonamides (cotrimoxasole). Deep surgical debridement is often essential.

Prior to the introduction of immunosuppressive or immunomodulatory therapies (e.g. TNF-alpha inhibitors) a latent underlying mycobacterial infection has to be excluded to avoid a risk of reactivation.