Actinomycetoma: An Update on Diagnosis and Treatment
Mycetoma is a chronic infection that develops after traumatic inoculation of the skin with either true fungi or aerobic actinomycetes. The resultant infections are known as eumycetoma or actinomycetoma, respectively. Although actinomycetoma is rare in developed countries, migration of patients from endemic areas makes knowledge of this condition crucial for dermatologists worldwide. We present a review of the current concepts in the epidemiology, clinical presentation, diagnosis, and treatment of actinomycetoma.
Practice Points
- Diagnosis of actinomycetoma is based on clinical manifestations including increased swelling and deformity of affected areas, presence of granulation tissue, scars, abscesses, sinus tracts, and a purulent exudate containing microorganisms.
- The feet are the most commonly affected location, followed by the trunk (back and chest), arms, forearms, legs, knees, and thighs.
- Specific diagnosis of actinomycetoma requires clinical examination as well as direct examination of culture and biopsy results.
- Overall, the cure rate for actinomycetoma ranges from 60% to 90%.
Treatment of Actinomycetoma
Precise identification of the etiologic agent is essential to provide effective treatment of actinomycetoma. Without treatment, or in resistant cases, progressive osseous and visceral involvement is inevitable.9 Actinomycetoma without osseous involvement usually responds well to medical treatment.
The treatment of choice for actinomycetoma involving Nocardia brasiliensis is a combination of dapsone 100 to 200 mg once daily and trimethoprim-sulfamethoxazole (TMP-SMX) 80/400 to 160/800 mg once daily for 2 to 3 years.10 Other treatments have included the following: (1) amikacin 15 mg/kg or 500 mg intramuscularly twice daily for 3 weeks plus dapsone 100 to 200 mg once daily plus TMP-SMX 80/400 to 160/800 mg daily for 2 to 3 years (amikacin, however, is expensive and potentially toxic [nephrotoxicity and ototoxicity] and therefore is used only in resistant cases); (2) dapsone 100 to 200 mg once daily or TMP-SMX 80/400 to 160/800 mg daily for 2 to 3 years plus intramuscular kanamycin 15 mg/kg once daily for 2 weeks at the beginning of treatment, alternating with rest periods to reduce the risk for nephrotoxicity and ototoxicity10; (3) dapsone 1.5 mg/kg orally twice daily plus phosphomycin 500 mg once daily; (4) dapsone 1.5 mg/kg orally twice daily plus streptomycin 1 g once daily (14 mg/kg/d) for 1 month, then the same dose every other day for 1 to 2 months monitoring for ototoxicity; and (5) TMP-SMX 80/400 to 160/800 mg once daily for 2 to 3 years or rifampicin (15–20 mg/kg/d) plus streptomycin 1 g once daily (14 mg/kg/d) for 1 month at the beginning of treatment, then the same dose every other day for 2 to 3 months until a total dose of 60 g is administered, monitoring for ototoxicity.11 Audiometric tests and creatinine levels must be performed every 5 weeks during the treatment to monitor toxicity.10
The best results for infections with A pelletieri, A madurae, and S somaliensis have been with streptomycin (1 g once daily in adults; 20 mg/kg once daily in children) until a total dose of 50 g is reached in combination with TMP-SMX or dapsone12 (Figure 5). Alternatives for A madurae infections include streptomycin plus oral clofazimine (100 mg once daily), oral rifampicin (300 mg twice daily), oral tetracycline (1 g once daily), oral isoniazid (300–600 mg once daily), or oral minocycline (100 mg twice daily; also effective for A pelletieri).
More recently, other drugs have been used such as carbapenems (eg, imipenem, meropenem), which have wide-spectrum efficacy and are resistant to β-lactamases. Patients should be hospitalized to receive intravenous therapy with imipenem.2 Carbapenems are effective against gram-positive and gram-negative as well as Nocardia species.13,14 Mycetoma that is resistant, severe, or has visceral involvement can be treated with a combination of amikacin and imipenem.15,16 Meropenem is a similar drug that is available as an oral formulation. Both imipenem and meropenem are recommended in cases with bone involvement.17,18 Alternatives for resistant cases include amoxicillin–clavulanic acid 500/125 mg orally 3 times daily for 3 to 6 months or intravenous cefotaxime 1 g every 8 hours plus intramuscular amikacin 500 mg twice daily plus oral levamisole 300 mg once weekly for 4 weeks.19-23
For resistant cases associated with Nocardia species, clindamycin plus quinolones (eg, ciprofloxacin, moxifloxacin, garenoxacin) at a dose of 25 mg/kg once daily for at least 3 months has been suggested in in vivo studies.23
Overall, the cure rate for actinomycetoma treated with any of the prior therapies ranges from 60% to 90%. Treatment must be modified or stopped if there is clinical or laboratory evidence of drug toxicity.13,24 Surgical treatment of actinomycetoma is contraindicated, as it may cause hematogenous dissemination.
Prognosis
Actinomycetomas of a few months’ duration and without bone involvement respond well to therapy. If no therapy is provided or if there is resistance, the functional and cosmetic prognosis is poor, mainly for the feet. There is a risk for spine involvement with mycetoma on the back and posterior head. Thoracic lesions may penetrate into the lungs. The muscular fascia impedes the penetration of abdominal lesions, but the inguinal canals can offer a path for intra-abdominal dissemination.4 Advanced cases lead to a poor general condition of patients, difficulty in using affected extremities, and in extreme cases even death.
The criteria used to guide the discontinuation of initial therapy for any mycetoma include a decrease in the volume of the lesion, closure of fistulae, 3 consecutive negative monthly cultures, imaging studies showing bone regeneration, lack of echoes and cavities on echography, and absence of grains on examination of fine-needle aspirates.11 After the initial treatment protocol is finished, most experts recommend continuing treatment with dapsone 100 to 300 mg once daily for several years to prevent recurrence.12
Prevention
Mycetoma is a disease associated with poverty. It could be prevented by improving living conditions and by regular use of shoes in rural populations.2
Conclusion
Mycetoma is a chronic infection that develops after traumatic inoculation of the skin with either true fungi or aerobic actinomycetes. The resultant infections are known as eumycetoma or actinomycetoma, respectively. The etiologic agents can be found in the so-called grains. Black grains suggest a fungal infection, minute white grains suggest Nocardia, and red grains are due to A pelletieri. Larger white grains or yellow-white grains may be fungal or actinomycotic in origin.
Specific diagnosis requires direct examination, culture, and biopsy. The treatment of choice for actinomycetoma by N brasiliensis is a combination of dapsone 100 to 200 mg once daily and TMP-SMX 80/400 to 160/800 mg once daily for 2 to 3 years. Other effective treatments include aminoglycosides (eg, amikacine, streptomycin) and quinolones. More recently, some other agents have been used such as carbapenems and natural products of Streptomyces cattleya (imipenem), which have wide-spectrum efficacy and are resistant to β-lactamases.
