Fishtank Granuloma

Key Points
Caused by a species of bacteria related to tuberculosis
One form of “atypical mycobacterial” infection
Presents as crusted nodules on the skin
Can manifest in different parts of the body, depending on the causative bacteria

Atypical Mycobacterial infection is caused by an infection by a mycobacterial bacteria related to that which causes Tuberculosis. In the skin, it often consists of crusted nodules or abscesses.

Atypical Mycobacterial infection can develop in anyone with exposure to the bacteria, and those forms that affect the skin are mycobacterium ulcerans, mycobacterium chelonae, and mycobacterium marinium. While the ulcerans and marinium forms of the bacteria have very specific areas of exposure, mycobacterium chelonae is prevalent in many water sources, including tap water.

Mycobacterium marinum is uncommon, and generally appears most often in those with exposure to infected fresh or saltwater. In addition to lesions which most often affect the knees, elbows and extremities, it may, in rare cases, cause swollen and tender joints. Mycobacterium ulcerans is most common in Central and West Africa in wet areas, but has also been reported in Australia. Severe forms of this infection can destroy blood vessels, nerves and even spread to bone, and lesions can spread to up to 15% of the body. Mycobacterium Chelonae, the most widespread form of the infection, can cause lung disease, and infections of the eye, joints, and various other organs, in addition to the formation of non-healing Wounds and subcutaneous nodules or abscesses.

Differential Diagnosis (Other conditions with similar appearance)

Multifocal Kaposi sarcoma

Sporotrichosis or other deep fungal infection

Cat scratch disease
Toxoplasmosis

Tularemia

Diagnosis
Key Points
Diagnosis initially based on skin appearance
Testing will be done to confirm the presence of bacteria and determine which form of the condition is extant and to rule out other, similar-appearing conditions

Initially diagnosed by appearance, health care professionals will test to determine which type of the bacteria causing Atypical Mycobacterial infection is present, and to rule out other conditions which may have similar presentation of symptoms.

Treatment
Treatment often involves a course of antibiotics
Different forms of the condition may require differing treatment

Treatment consists of a course of antibiotics, most commonly Rifampicin, Ethambutol, Isoniazid, Minocycline, Ciprofloxacin, Clarithromycin, Azithromycin, and Cotrimoxazole, and often a combination. Mycobacterium Marinum is often resistant to isoniazid. Mycobacterium chelonae is best treated by clarithromycin in combination with another drug. In some cases surgical excision of the lesions is considered.