Differential Diagnosis

  • Bacterial abscess
  • Cutaneous anthrax
  • Granuloma annulare
  • Mycobacterium marinum infection
  • Vasculitis


This patient was diagnosed with Mycobacterium marinum infection, an atypical mycobacterial skin infection often contracted from contaminated fish tanks, swimming pools, and, occasionally, ocean or lake water.



  • The typical skin lesion consists of a pustule or nodule and develops on the exposed extremity 2─3 weeks after exposure
  • Constitutional symptoms are rare; fever, if present, is typically low-grade


Pearls for Urgent Care Management and Considerations for Transfer

  • The disease is usually self-limited, and lesions tend to heal over a period of 1─2 years if left untreated
  • Patients with AIDS, organ transplant recipients, and patients on chronic steroids may occasionally develop disseminated infections to the skin, bone marrow, and joints, leading to synovitis and arthritis


Acknowledgment: This case is presented courtesy of VisualDx.

A 27-Year-Old Man with a Lesion on One Hand
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