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skin infection with tenosynovitis successfully treated with doxycycline

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Mycobacterium marinum skin infection with tenosynovitis successfully treated with doxycycline
Filipa Osorio MD1, Sofia Magina MD1,2, Teresa Carvalho3, Maria Helena Goncalves3, Filomena Azevedo MD1
Dermatology Online Journal 16 (9): 7

1. Department of Dermatology and Venereology, Hospital de Sao Joao E.P.E., Porto, Portugal.
2. Faculty of Medicine of University of Porto, Portugal
3. Department of Microbiology, Hospital de Sao Joao E.P.E., Porto, Portugal


Skin infection with Mycobacterium marinum can rarely spread to deeper structures, making it more difficult to treat. We report a case of a M. marinum skin infection and hand tenosynovitis that showed a good response to monotherapy with doxycycline in spite of severe hand movement impairment.


Infection with Mycobacterium marinum is uncommon and it usually occurs as a skin disease, but it can rarely spread to deeper structures [1, 2, 3]. There is no consensus about the most appropriate therapeutic regimen, although case series point to the use of two or more drugs, especially when there is deeper structure involvement [4].

Case report

Figure 1
Figure 1. Clinical presentation

An immunocompetent 80-year-old man presented to our department with three confluent erythematous to violaceous nodules on the dorsum of the right hand. He complained of mild local pain and pruritus and purulent discharge, lasting for 15 days. He worked with fish and birds without gloves and he reported a skin injury in the right hand one month before. Flucloxacillin and a betamethasone and fusidic acid cream had been prescribed with no relief. Other than a known history of cardiac valve disease, high blood pressure, and total left knee arthroplasty, he had no other medical problems. He was taking warfarin, telmisartan/hydrochlorothiazide, calcium and alprazolam.

At this point, we performed a skin biopsy and started empirical treatment with itraconazole 100 mg BID.

Figure 2Figure 3
Figures 2 and 3. Histological picture

The biopsy showed an epidermis with acanthosis and papillomatosis. In the dermis there was a lymphohistiocytic and plasma cell infiltrate, with numerous multinucleated giant cells, sometimes forming granulomas without caseation. Periodic-acid Schiff and Ziehl-Neelsen stains did not reveal fungi or mycobacteria. Polymerase chain reaction (PCR) was negative for fungi and mycobacteria in the skin.

Figure 4Figure 5
Figures 4, 5, and 6. After 6 weeks of itraconazole

Figure 6

Six weeks later there was no improvement and the patient presented with two more nodules on the arm and forearm and significant hand edema. There was also a severe decrease in range-of-motion in the right hand. An ultrasound study was compatible with soft tissue infection and tenosynovitis. The patient suspended treatment with itraconazole and started doxycycline 100mg BID.

Meanwhile, after 6 weeks of incubation, Mycobacterium marinum was found on skin culture.

Figure 7Figure 8
Figures 7, 8, and 9. Clinical resolution after 14 weeks of doxycycline

Figure 9

After 10 weeks of treatment with doxycycline, there was complete clearing of cutaneous lesions and restoration of range-of-motion. Therapy was extended until a total of 14 weeks were completed; there were no other complications.


Mycobacterium marinum skin infection frequently occurs because of exposure to contaminated water [1, 5]. Trauma seems to play a role [6]. In most cases the upper limb is affected [2, 5, 7]. The clinical appearance is variable and includes papules, plaques, and nodules, with or without ulceration [6]; a sporotrichoid distribution of papules and nodules may be seen [5, 8]. Less frequently the infection can affect deeper structures [1, 2, 3], most commonly in immunocompromised patients [6]. Our patient was an immunocompetent man with a fish-related hobby and history of trauma, who presented with a M. marinum skin infection and tenosynovitis on the upper limb.

Histological findings vary from a nonspecific inflammatory infiltrate in the first few months to granulomas in older lesions [9]. In this case, although the lesions were only two-weeks-old, granuloma formation was already evident. Fast acid bacilli are frequently negative, as it was in this case [2, 7]. Cultures have been reported positive in 70 to 80 percent of cases [8], but results are typically late because M. marinum is a slow-growing mycobacteria [6]. Here the result was not available until 6 weeks after the biopsy. PCR analysis can give a more rapid diagnosis, but it was negative in our case [10]. Imaging studies should be made if indicated by the history. Because of the range-of-motion impairment, ultrasound was performed and it revealed tenosynovitis.

The most appropriate therapeutic regimen for M. marinum has not been defined in clinical trials but reported cases have been successfully treated with antibiotics (tetracyclines - minocycline, doxycycline; co-trimoxazole; macrolides - clarithromycin, azithromycin; quinolones - ciprofloxacin; aminoglycosides - amikacin), antimycobacterials (rifampicin, rifabutin, ethambutol) and surgery, in single or combination regimens. M. marinum is a multi-drug resistant species. In vitro results do not necessarily correlate with in vivo success. Therefore, routine susceptibility testing is not recommended. Infections localized to skin and subcutaneous tissue have been treated with monotherapy, but a combination regimen with 2 or more drugs has been preferred to treat deeper structure infections because failure has been significant in these cases [4, 5].

The duration of therapy varies markedly in the literature, ranging from one month to one and a half years; it is longer for patients with infection spread to deeper structures [5]. Three months is considered the average duration and it is recommended to continue therapy for 4-6 weeks after clinical resolution of lesions [4].

This case shows a good response to 14 weeks of monotherapy with doxycycline in spite of the tenosynovitis with severe functional impairment. Resolution was observed at week 10 but therapy was given for 4 more weeks.


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