A 30-year-old male presented with about one year history for a solitary pustular plaque on his finger. He was a .... fancier. There was no lymphadenopathy and he had no response to antibiotics (topical mupirocin and oral cephalexin). The patient had not any significant medical problem. 

What is your diagnosis? 

What do you recommend for treatment?

Diagnosis: Fish Tank Granuloma

Swimming poor garnuloma or fish tank granuloma is caused by Mycobacterium marinum. The natural habitat of this organism is water, particularly enclosures of water that are not often replenished.

Fish tank granuloma usually begins as a violaceous papule at the site of a trauma about 2 to 3 weeks after inoculation. Patients may present with an ulcerated plaque or a psoriasisform lesion usually on the hands. As a rule, lesions are solitary but occasionally a centripetal spread reminiscent of sporotrichosis develops.

As in all mycobacterial diseases, the diagnosis requires a high index of suspicion and a history of fish handling helps in diagnosis.

This patient was also a fish fancier. Fortunately, he had a very good response to cotrimoxazole and doxycycline.

 Omid Zargari, MD