Updated: 10/4/2016

Atypical Mycobacterium Infections

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https://upload.orthobullets.com/topic/6107/images/m. marinum culture.jpg
  • Nontuberculous mycobacterial infections
  • Epidemiology
    • demographics
      • often found in marine workers
    • location
      • hand and wrist are involved in 50% of cases
    • risk factors
      • immunocompromised host
  • Pathophysiology
    • incubation
      • average incubation period is two weeks, but can be up to six months
      • average time to diagnosis and appropriate treatment is more than 1 year
    • organisms  
      • widely encountered in the environment, but rarely cause human pathology
        • M. marinum 
          • most common atypical mycobacterium infection
          • more common in stagnant fresh or salt water (aquariums)
        • M kansasii
          • found in soil
        • M terrae
          • found in soil
        • M. avium intracellulare
          • most common in terminal AIDS patients, but can occur in non-HIV patients
  • Prognosis
    • natural history
      • early presentation includes papules, nodules, and ulcers
      • late presentation may have progressed to tenosynovitis, septic arthritis, or osteomyelitis
    • morbidity & mortality
      • mortality rate is 32%
  • Symptoms
    • cutaneous rash with discomfort
  • Physical exam
    • papules, ulcers, and nodules are common, especially on the hands
      • many times presents with a single nodule that may ultimately spread to the lymph nodes
      • indistinguishable from tuberculous mycobacterial infection
  • Histology
    • granulomas may or may not demonstrate acid-fast bacilli on AFB stain
  • Cultures and sensitivities are key to diagnosis
    • Lowenstein-Jensen culture agar
      • M. marinum incubated specifically at 30 to 32° C 
      • M. avium intracellulare incubated at room temperature
  • Nonoperative
    • oral antibiotics
      • indications
        • if diagnosed at early stage 
      • medications
        • ethambutol, tetraycline, trimethoprim-sulfamethoxazole, clarithromycin, azithromycin
        • add rifampin if osteomyelitis present
  • Operative
    • surgical debridement + oral antibiotics in combination for 3 to 6 months
      • indications
        • later stage disease
      • use a combination of above medications

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