Abstract
Mycobacterium chelonae can be difficult to treat because of inherent resistance to many available antimicrobials. We present a case of a multidrug-resistant M. chelonae skin infection in a 52-year-old woman who presented with a 3- to 4-week history of painful, erythematous nodules on the bilateral lower extremities. She demonstrated dramatic improvement at her 4-week follow-up on omadacycline.
Keywords: Dermatology, infectious disease, Mycobacterium chelonae, rapidly growing Mycobacteria
Mycobacterium chelonae is a nontuberculous rapidly growing Mycobacteria responsible for serious skin and soft tissue infections. Because of its inherent resistance to many of the available antimicrobials, it can be difficult to treat. Newer drugs with documented efficacy, high oral bioavailability, and less adverse effects are now available for use, although clinical experience is lacking. We present a case of a multidrug-resistant M. chelonae skin infection successfully treated with a new tetracycline, omadacycline.
CASE DESCRIPTION
A 52-year-old woman with an extensive history of nonhealing lower-extremity erosions and ulcerations presented to our clinic with a 3- to 4-week history of new painful, erythematous nodules on both legs. She was paraplegic due to a motor vehicle accident in the 1980s and was first seen in the clinic several months earlier with painful lesions on her legs thought to be contact dermatitis secondary to use of over-the-counter topicals and lotions. She was treated with topical steroids and a prednisone taper. She was seen several more times reporting severe, intense burning pain, and a diagnosis of complex regional pain syndrome was favored. She was given another prednisone taper and referred for a lumbar sympathetic nerve block, which improved her pain. Several months later, she presented with multiple bright red 1- to 2-cm nodules on her legs extending from the distal thighs to the ankles (Figure 1a). Some of the nodules drained yellow, purulent fluid. A culture of the fluid was inoculated in Lowenstein-Jensen and Middlebrook 7H9 media and grew M. chelonae, resistant to multiple antibiotics including clarithromycin, the mainstay of treatment. To avoid hospital admission for intravenous antibiotics, and after omadacycline testing resulted in a minimum inhibitory concentration of 0.25 μg/mL, she was placed on a novel tetracycline, omadacycline. She received an initial oral loading dose of 450 mg on days 1 and 2 and continued with 300 mg orally once daily for 4 months with dramatic improvement (Figure 1b). The lesions were still resolved at 1-year follow-up.
Figure 1.
(a) Multiple erythematous 1- to 2-cm nodules with ulcerations on the anterior leg before treatment. (b) The anterior leg at 4-week follow-up.
DISCUSSION
M. chelonae causes a wide array of human infections. In immunosuppressed patients, it frequently causes pulmonary disease or hematogenously disseminated disease. In the immunocompetent host, isolated skin and soft tissue infections are more common. Historically, several outbreaks of M. chelonae infection have been associated with cosmetic surgery, pedicures, or tattoos because of its viability in an aqueous environment. 1 The clinical exam may show recurrent abscesses, nodules with purple discoloration, or chronic draining sinuses. 2 Our patient’s use of steroids as well as multiple over-the-counter emollients that may have been contaminated likely predisposed her to infection.
In the past, a variety of antimicrobials were useful in the treatment against rapidly growing mycobacteria including doxycycline, trimethoprim-sulfamethoxazole, levofloxacin, and clarithromycin. However, there is growing resistance among the most common rapidly growing mycobacteria species (M. abscessus, M. chelonae, M. fortuitum). 3 One drug frequently used to treat these resistant species, intravenous tigecycline, is difficult for patients to tolerate because of its gastrointestinal side effects. A new semisynthetic tetracycline, omadacycline, was designed in both intravenous and oral forms with the goal of avoiding common tetracycline side effects as well as resistance mechanisms, such as efflux pumps and ribosomal protection. 4
Omadacycline has demonstrated efficacy noninferior to linezolid for treating acute bacterial skin and skin structure infections. 5 An in vitro study conducted by Shoen et al showed omadacycline with a favorable 90th percentile minimum inhibitory concentration of 0.25 μg/mL against M. chelonae and concluded the new tetracycline has the potential to improve outcomes for these infections. 4
To our knowledge, no previous case reports described successful treatment with omadacycline for isolated cutaneous involvement. This case demonstrates the efficacy of omadacycline against M. chelonae skin and skin structure infection. Omadacycline at a dose of 300 mg orally each day was given to our patient for 4 months with impressive success.
References
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