This man had first noticed swelling on the back of his hand about nine months earlier. His GP had made a diagnosis of arthritis and prescribed an NSAID to ease the symptoms.
Six months later he was alarmed by the development of two erythematous/bluish nodules in the area of the swelling, which subsequently broke down and ulcerated.
The GP then prescribed a course of flucloxacillin, assuming a bacterial infection. When there was no response and lesions seemed to be spreading up his arm along the line of the lymphatic drainage, together with enlarged lymph glands in the axilla, the patient was referred to the dermatologist.
What is the diagnosis, management and differential diagnoses?
DIAGNOSIS AND MANAGEMENT
A swab was taken from the lesion but, in view of the history, appearance of the lesion and the fact that the patient kept tropical fish, a clinical diagnosis of fish tank granuloma was made.
As in this case, it is common for fish tank granuloma to be initially misdiagnosed and treatment delayed. The diagnosis may be confirmed by a swab for culture and sensitivities. If this is inconclusive, the lesion may be biopsied.
The organism is usually sensitive to rifampicin, tetracycline, co-trimoxazole or clarithromycin. Resolution may take several months and the drug should be continued for four to six weeks after clearance of the lesions. Surgical drainage or debridement is not usually necessary unless the patient experiences persistent pain.
POSSIBLE DIFFERENT DIAGNOSES
- Rheumatoid arthritis
- Squamous cell carcinoma
- Caused by parasites of the genus Leishmania and transmitted by sandfly bites.
- Small papules gradually enlarge to form dark red, firm, indurated nodules.
- Crust forms on surface, which then ulcerates.
- Usually on exposed areas such as the face.
- Usually a clinical diagnosis but may be confirmed if parasite found in biopsy.