Mycobacterial skin infections

It is important to consider mycobacterial infection in any stubborn and atypical skin problem, particularly in immunocompromised individuals.¹ Mycobacteria cause slowly developing chronic skin infections.

Mycobacterial infection is increasing, partly due to emerging drug resistance and the HIV epidemic.

Non-tuberculous mycobacteria (NTM) are acid-fast bacteria, widespread in the environment. In children, NTM may cause lymphadenitis, skin and soft tissue infections and occasionally also lung disease and disseminated infections.² NTM cause infections mainly after trauma, surgery and cosmetic procedures.³

Of the greater than 140 NTM species reported, 25 species have been strongly associated with NTM diseases and the other species are rarely encountered in clinical samples. Correct species identification is very important but the diagnosis is often complex. NTM species vary greatly in their growth rate, temperature tolerance and drug susceptibility.⁴

Tuberculosis

Lupus vulgaris⁵

• This is the most common form of cutaneous tuberculosis, occurring after primary infection in individuals with good natural resistance.

• Females are more often affected and it is also more common in children.

• Most commonly, it affects the face and neck and is seen initially as firm, translucent, brown nodules.

• Without treatment, the lesions slowly spread laterally, leading to disfiguring scarring. Malignant change has been reported in these scars.

• Diagnosis is confirmed by biopsy and culture. Patients should receive full anti-tuberculous therapy for at least one year.

Scrofuloderma⁶

• Scrofuloderma results from breakdown of skin overlying a tuberculous focus, usually at a lymph node but also at the skin over infected bones or joints.

• Lesions present as firm, painless, subcutaneous nodules that gradually enlarge and suppurate, then form ulcers and sinus tracts in overlying skin. Typical ulcers have undermined edges and a floor of granulation tissue. It causes fistulae and scarring.

• Mycobacterium tuberculosis can be identified both in the nodes and in the material draining on to the skin surface.

• Full anti-tuberculous therapy and surgical excision are required.

Warty tuberculosis⁷

• Also known as tuberculosis verrucosa cutis.

• This is the most common form of cutaneous tuberculosis in developing countries but it is rare in western countries.

• It occurs with infection in someone who has immunity from previous infection.

• It causes a warty plaque, often on the hands, knees or buttocks.

Tuberculides

• Skin reactions to systemic tuberculosis - eg, erythema nodosum, erythema induratum (Bazin's disease).

Leprosy (Hansen's disease)⁸

Leprosy is caused by Mycobacterium leprae and Mycobacterium lepromatosis. Both of these primary affect the skin and peripheral nerves. Contrary to popular belief, it is not highly contagious. Treatment is readily available and early intervention significantly reduces disability. Any damage caused by neuropathy is irreversible and may require lifelong care.

Environmental mycobacterial diseases

• Cutaneous infections with atypical mycobacterium are much more common in immunosuppressed patients, especially those with HIV infection, or leukaemia or in those undergoing immunosuppressive therapy.

• Atypical mycobacterial infections are also more common in the elderly.

• The environmental mycobacteria cause two named diseases with characteristic features:
  

  • Fish tank (or swimming pool) granuloma caused by Mycobacterium marinum.

  • Buruli ulcer caused by Mycobacterium ulcerans infection.

• The other mycobacterioses are much less specific, often resembling tuberculosis.

Buruli ulcer⁹

• Buruli ulcer is also known as Bairnsdale ulcer or Searls' ulcer (Australia) and Kakerifu ulcer or Toro ulcer (Congo).

• It is a re-emerging infection and is now the third most prevalent mycobacterial disease worldwide, behind tuberculosis and leprosy.

• It is due to infection by M. ulcerans in tropical zones - acquired from vegetation or water after trauma.

• Initially a painless erythematous nodule develops, usually on the leg or forearm. This eventually becomes necrotic and ulcerates.

• Treatment is usually by wide surgical excision - antimicrobial therapy with rifampicin and clarithromycin is recommended before and after surgery.

• Bacillus Calmette-Guérin (BCG) vaccine gives short-term prevention.

Fish tank (or swimming pool) granuloma¹⁰

• This is caused by M. marinum infection, which infects fish and is also found in swimming pools.

• Typically, it causes a reddish, slightly scaly plaque on the hand or arm of someone who keeps tropical fish.

• M. marinum is sensitive to minocycline, clarithromycin, amikacin, rifampicin, ethambutol and doxycycline.

Other environmental mycobacteria

• Mycobacterium kansasii:
  

  • Most patients who present with localised primary cutaneous M. kansasii infection are immunocompetent, whereas most patients with disseminated or pulmonary infection are immunocompromised.

  • It may resemble cellulitis or sporotrichosis.

  • It may also present with tenosynovitis, cutaneous lymphadenitis; the clinical presentation is similar to that expected in lupus profundus and with ulcerative perineal lesions.

• Mycobacterium malmoense: cervical lymphadenitis in preschool-aged children. It has also been associated with cutaneous nodules on the hands.

• Mycobacterium szulgai: cellulitis, nodules and plaques.

• A case of disseminated Mycobacterium simiae infection with blood, pulmonary and cutaneous localisation has been reported.

• Mycobacterium gordonae: granulomatous synovitis and bursitis. It is sometimes called tap water scotochromogen. It has also caused granulomatous nodules on the back of the hand.

• Mycobacterium haemophilum: multiple, tender, cutaneous nodules, which may develop into ulcers or abscesses. They are often situated over limb joints. May lead to muscle wasting, tenosynovitis and joint effusions.

• Mycobacterium avium complex (MAC): this has emerged as a major human pathogen. Cutaneous disease is caused by direct inoculation (trauma, surgery, injection) and is characterised by skin lesions, such as ulceration, abscess or erythematous plaque.¹¹

Lymphadenitis¹²

• This mainly affects otherwise healthy children aged under 5 years.

• It usually affects the cervical lymph nodes, often just a single node.

• Is caused by many mycobacterial species, most often MAC and Mycobacterium scrofulaceum.

• Infection in older children and more diffuse involvement are often associated with HIV infection.

• Surgical excision is curative.

Investigations¹³

• Careful clinical examination is the gold standard.

• The optimal way to make the diagnosis is by performing a culture of tissue. Most mycobacteria require special culture conditions, which, if not specifically requested, are frequently not used.

• The development of DNA fingerprinting technology, especially pulsed-field gel electrophoresis, has been suggested as a diagnostic tool.

• Polymerase chain reaction has been used to aid diagnosis.

• CXR: associated pulmonary disease.

• The purified protein derivative test (antigen skin test used to aid the diagnosis of tuberculosis) result is usually negative in infections with atypical mycobacteria.

Mycobacterial skin infection treatment and management¹³

• Effective treatment depends on precise diagnosis and identification of the underlying organism. Treatment will also be governed by results of culture and sensitivity.

• Treatment of atypical mycobacterial skin infections is often difficult because many atypical mycobacteria are resistant to common antibiotics.

• A combined therapeutic approach, including surgical drainage, debridement and prolonged treatment with combined antimicrobial agents, has been used in some cases of atypical mycobacteria.

• In some cases (especially fast-growing environmental mycobacteria), successful treatment requires aggressive debridement of all infected subcutaneous tissues and skin.

Complications

Scarring and nerve damage can occur from long-standing untreated infections.

Prognosis

The prognosis is good with proper medical and surgical treatment.

However, many patients are often not properly treated because of insufficient health resources in developing countries, or treatment may be difficult because of underlying immunosuppression and consequent diffuse infection.

Prevention

• Avoidance of contaminant material.

• BCG vaccination gives a variable degree and duration of protection.