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Differential Diagnosis

  • Mycobacterium chelonae infection
  • Mycobacterium marinum infection
  • Cutaneous phaeohyphomycosis infection
  • Foreign body granuloma
New ulcer on one hand


This is Myobacterium marinum infection. M marinum is an atypical mycobacterial skin infection contracted from contaminated fish tanks, swimming pools, lake water and salt water. Minor trauma is a predisposing factor.

Men are affected more commonly than women.

Learnings/What to Look for

  • The typical skin lesion consists of a pustule or nodule and develops 2–3 weeks after exposure
  • Nodules may ulcerate, suppurate, and spread via lymphangitic spread (about 25% of cases)
  • In more severe infections, deeper manifestations such as tenosynovitis, arthritis, bursitis, or osteomyelitis may be seen
  • In immunosuppressed patients, disease can disseminate to the lungs or other systems; bacteremia is rare

Pearls for Urgent Care Management

  • Infection is usually mild and self-limited, with lesions healing over 1 to 2 years if left untreated
  • Treatments found to expedite healing include minocycline, clarithromycin, doxycycline, and trimethoprim-sulfamethoxazole
  • While M marinum is naturally multidrug-resistant, drug resistance varies. As such, combination therapy may be required
  • Cryotherapy, x-ray therapy, electrodesiccation, photodynamic therapy, and local hyperthermic therapy have also been reported to be effective

Acknowledgment: Image and case presented by VisualDx (

A 43-Year-Old Woman with a New Ulcer on One Hand