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Subcutaneous nodules with sporotrichoid spread

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Subcutaneous nodules with sporotrichoid spread
Mark N Schwendiman1, Ryan P Johnson MD MPH2, J Scott Henning DO2
Dermatology Online Journal 15 (5): 11

1. Des Moines University College of Osteopathic Medicine and Surgery, Des Moines, Iowa
2. San Antonio Military Medical Center, Dermatology Department, Lackland AFB, Texas.


Background: Mycobacterium marinum is an atypical mycobacterium found worldwide and associated with swimming pools and aquariums. Infections typically present with subcutaneous nodules and lymphangitis. Case report: A 61-year-old female presented with a two-month history of subcutaneous nodules. The patient had a significant recent history that included rose gardening and cleaning her aquarium at home. Biopsy for histology and tissue culture proved the presence of infection with Mycobacterium marinum and the patient was treated with minocycline. The nodules eventually healed and no new lesions appeared after initiation of treatment. Conclusion: Mycobacterium marinum is one of many entities that must be considered in a patient with ascending nodules along the lymphatic drainage of an extremity.


Mycobacterium marinum is an atypical mycobacterium found in both freshwater and saltwater. M. marinum is classified in Runyon group 1 and is a photochromogen, capable of producing pigment when cultured and exposed to light. Aquarium workers, swimmers, anglers, or marine enthusiasts are at highest risk for inoculation. Although still rare, improper chlorination and emergence of chlorine-resistant organisms have produced an increase in pool-associated exposures [1]. Initial infection occurs following inoculation of previously injured or wounded skin. An extensive review of the literature by Farr and Jernigan revealed that the median incubation period is 21 days, with a range from 5-270 days [1]. Patients present with papules, nodules, or ulcers at the site of trauma. Patients might also complain of localized pain and induration. Fever and generalized lymphadenopathy from systemic involvement is typically limited to the immunocompromised. If not properly treated, the mycobacteria can ascend along the path of draining lymphatic flow, described as sporotrichotic spread. More complicated infections can cause tenosynovitis progressing to septic arthritis or osteomyelitis [2].

Clinical synopsis

A 61-year-old female presented to the dermatology clinic at Wilford Hall Medical Center as a consult from the Infectious Disease service for subcutaneous nodules that had begun two months prior. The nodules started on the tip of the patient's right index finger and had spread proximally up her right forearm. The patient thought that the first nodule may have been caused by a splinter, admitting to feeling a foreign body sensation despite any known history of trauma. The patient had previously tended to her rose garden at home and cleaned her aquarium within the month. Her primary care physician had attempted treatment with both ciprofloxacin and amoxicillin.

Figure 1Figure 2

Physical examination revealed multiple, discrete, 3 mm to 1 cm erythematous nodules located on the right dorsal hand, wrist, and forearm (Figs. 1 & 2). The nodules were neither tender nor fluctuant.

Laboratory stains of the biopsy revealed acid-fast bacilli. Culture results confirmed Mycobacterium marinum.

Figure 3Figure 4

Histopathology: punch biopsy revealed mid-dermal abscess and superficial and deep granulomatous inflammation (Figs. 3 & 4). Fite stain revealed one positive organism.

Before culture and stain results were available, Mycobacterium marinum was the presumed cause. The patient empirically began treatment with minocycline 100mg twice daily. However, after only two doses of the medication she requested a change in medication because of symptoms of vertigo. Doxycycline 100 mg twice daily was then started; the original lesions remained stable with no new nodules appearing. She tolerated the medication well but her active lesions never completely cleared. She also admitted to missing doses. After four months of doxycycline without resolution, another four-month course of clarithromycin 500 mg twice daily and ethambutol 1200 mg daily was initiated. This produced clearing of the remaining nodules after two months; she was then given an additional two months of this same regimen. She did have some residual erythematous scars that persisted after therapy but never had any signs of tenosynovitis or osteomyelitis.


Mycobacterium marinum is unique from other mycobacteria for a variety of reasons. Notably the organism, a non-motile acid-fast bacilli, grows at 30-32°C (86-89.6°F). Perhaps the strict temperature requirement is the reason why the infection is almost always seen on the limbs where temperature is slightly lower than the core of the body. Mycobacterium marinum grows best on Lowenstein-Jensen media and the microbiology lab should be informed if M. marinum is suspected because the lab will typically culture at 37°C, which is inadequate for many atypical mycobacteria.

Mycobacteria are notorious for not growing in culture even under the most ideal conditions. One study showed that cultures grown at 30°C to 33°C may take at least two to four weeks and only 70 percent to 80 percent are positive [3]. A different review of M. marinum infections revealed that only 31 percent of biopsy specimens showed the presence of acid-fast bacilli [4]. Therefore, if the history and physical examination suggest M. marinum infection, empiric treatment should be strongly considered even in the absence of biopsy or culture confirmation.

Our case is unique because the patient's history suggested she could have had an exposure to pathogens located in either the soil or in water, due to her extensive gardening and home aquarium care. Particular pathogens in these environments might give rise to either "rose gardener's disease" or a "fish tank granuloma." These diseases are caused by Sporothrix schenckii and Mycobacterium marinum respectively. The organisms are among the common causes of sporotrichoid spreading nodules in the United States.

The differential diagnosis of subcutaneous nodules with sporotrichoid spread is extensive and is noted in Table 1. In addition to M. marinum and other atypical mycobacteria, Sporothrix schenckii and Nocardia species deserve special consideration due to their similar presentation.

Sporothrix schenckii is a dimorphic fungus which is the causative agent of sporotrichosis. This organism should be suspected as a cause in a patient who has a history of gardening, farming, or nursery work. Sporotrichosis also presents with sporotrichoid-spreading subcutaneous nodules. Being a fungus, Sporothrix schenckii is easily discerned from M. marinum on culture or histology. Sporotrichosis is best treated with itraconazole or saturated solution of potassium iodide (SSKI), rather than antibiotics used for M. marinum [5].

Nocardia, a filamentous gram-positive bacteria, stains with acid-fast just as M. marinum does. Nocardia, like S. schenckii, is also frequently found in the soil. Nocardia asteroides primarily affects the lungs and can disseminate systemically. However, Nocardia brasiliensis is often associated with sporotrichoid-spreading subcutaneous nodules. Sulfonamides, such as trimethoprim-sulfamethoxazole, are the antibiotics of choice for the treatment of cutaneous nocardiosis.

Relatively few studies have been conducted to determine the first line treatment for Mycobacterium marinum infections, most likely because of its rarity. Aubry et al. noted that in the past, M. marinum has been treated with tetracyclines, sulfamethoxazole and trimethoprim, rifampin plus ethambutol, clarithromycin, levofloxacin, and amikacin. Eighty-seven percent of the patients in their study were cured after therapy that included clarithromycin, rifampin, or tetracyclines. There were also treatment failures with the same antibiotics. Consequently, the most favorable treatment outcome could not be related to any specific antibiotic they reviewed [7].

Even with few documented cases, the general consensus from the dermatology literature suggests that minocycline, 100 mg twice daily, is particularly effective. Minocycline is also effective in cases complicated by delayed diagnosis and systemic immunosuppression [8]. The vertigo symptoms experienced by our patient are not unusual and may have resolved if the patient had been willing to continue. Extended release forms of minocycline may be less likely to produce this symptom. Clarithromycin 500mg twice daily has also been used effectively. Ethambutol hydrochloride 15-20 mg/kg/day plus rifampin 10 mg/kg/day has proved to be more effective than any single antibiotic regimen [3, 9]. In our paitent, we felt that optimal M. marinum treatment should include the two effective drugs for 1-2 months after resolution of lesions, typically 3-4 months in total. Of course, deeper infections may require more prolonged treatment and even surgical debridement [3].


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9. Edelstein H. Mycobacterium marinum skin infections. Report of 31 cases and review of the literature. Arch Intern Med. 1994 Jun 27;154(12):1359-64. [PubMed]

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