Mycobacterium Chelonae Infection Diagnosed by PCR in a Patient with Chronic Leg Nodules

Correct Answer. B. Infection arising in the setting of chronic stasis

This patient’s presentation of chronic, intermittently draining purpuric nodules on the right lower extremity in the setting of chronic venous stasis, along with biopsy findings of lipodermatosclerosis, focal microabscesses, and AFB and PCR-positive Mycobacterium organism, is consistent with a diagnosis of cutaneous M chelonae infection.

While rheumatoid vasculitis can present with purpuric or ulcerative lesions in patients with longstanding rheumatoid arthritis, it typically demonstrates fibrinoid necrosis and leukocytoclastic vasculitis on histopathology, which was absent in this case.¹ Lupus vasculitis shows similar histopathologic findings to rheumatoid vasculitis with varying clinical presentations, such as palpable purpura, urticaria plaques, or bullous lesions of the extremities. However, they are rarely nodular and persistent without other signs and symptoms of lupus (malar rash, photosensitivity, oral ulcers, serositis, renal disease).² Erythema nodosum usually presents with bilateral, non-ulcerated, tender nodules on the shins and is characterized by lobular or septal panniculitis with mixed inflammatory infiltrate on histology.³ Cutaneous polyarteritis nodosa is commonly associated with painful erythematous nodules on the lower extremity, livedo reticularis, and ulcerations with histology showing necrotizing vasculitis of small and medium-sized arteries.⁴ Erythema induratum (nodular vasculitis) is an extra-pulmonary manifestation of M. tuberculosis, which presents as persistent tender, erythematous, and indurated nodules on the lower legs with granulomatous septal panniculitis on histology.⁵

Treatment and management. Infectious disease evaluated the patient and initiated clarithromycin 500 mg twice daily (92-100% sensitive) and linezolid 600 mg once daily (50-100% sensitive) for 4-6 months of therapy, as tolerated.

Outcome and follow-up. The patient tolerated the clarithromycin well but reported feeling intoxicated after the first dose of linezolid, prompting discontinuation. At the same visit, she also reported oral soreness without visible mucosal changes. The linezolid was replaced with omadacycline 300 mg daily. However, her adherence to omadacycline has been inconsistent due to gastrointestinal upset. After 5 weeks of omadacycline 300 mg daily, the dose was reduced to 150 mg daily, with a planned course of 4-6 months of therapy. Approximately 6 months after her initial presentation, she reported that the leg nodules were less indurated and tender.

Discussion. M chelonae is a rapid-growing, gram-positive, acid-fast bacillus nontuberculous mycobacterium found in soil, water, and aquatic animals and can cause skin and soft tissue infections, especially in the extremities due to the organism's preference for lower temperatures.⁶ The clinical features vary but include erythematous or violaceous nodules, papules, and pustules that may evolve into ulcers or abscesses or take on a sporotrichoid pattern.⁷ Since the clinical presentation is typically nonspecific but often disseminated, especially in immunocompromised patients, this condition can often go undiagnosed or misdiagnosed for an extended period of time.⁸ In this case, the patient is on chronic corticosteroids for her rheumatoid arthritis, which suppresses her immune system, making her more susceptible to infections. Skin infections with M chelonae have also been reported following procedures such as sclerotherapy, tattooing, acupuncture, and cosmetic injections.⁶ Our patient’s history of prior trauma may have played a role in the development of infection in the right leg alone.⁹

Previously reported histologic findings of cutaneous M chelonae infections include neutrophilic dermal inflammation with mixed lymphocytes and histiocytes or neutrophilic abscesses with granulomatous inflammation. Reactive vasculopathy may be seen.^10,11 However, these histologic findings are nonspecific and not pathognomonic. Tissue gram, auramine, and PAS stains may be negative, as well as a mycobacterial culture (Mycobacteria Growth Indicator Tube). Identifying and diagnosing M chelonae often requires multiple tissue samples and PCR-based molecular diagnostics when cultures are inconclusive, especially in chronic or low-grade infections.^10,11

Although there is no standard treatment for cutaneous M chelonae, literature supports treatment with a prolonged 4 to 6-month course of multidrug antibiotic therapy to avoid relapse.¹² Treatment with standard antituberculosis medications is ineffective, as this organism is often resistant to these medications in addition to ciprofloxacin, cefotaxime, sulfamethoxazole, and doxycycline.^8,12 This organism is often sensitive to macrolides like linezolid, cefoxitin, fluoroquinolones, and tobramycin.^10,12 Clarithromycin is the first-line agent for most superficial infections, although resistance may occur.¹² In more complex or resistant cases, combination therapy with at least 2 antibiotics, commonly a macrolide with cefoxitin, amikacin, or imipenem, is recommended.¹⁰ Omadacycline, a newer tetracycline-class antibiotic, has been evaluated as an effective monotherapy in select cases, achieving clinical cure without recurrence at 1-year follow-up.¹⁰ New data also support the use of bacteriophage therapy as a novel adjunct therapy without inducing bacterial resistance.¹⁰ In this case, clarithromycin was selected as the primary therapy, with omadacycline as adjuvant therapy due to poor tolerance of linezolid.

This case is unique since it illustrates how cutaneous M chelonae infection may persist, undiagnosed, for years, particularly when the presentation is atypical or overlaps with other similarly presenting skin conditions. Physicians must keep atypical mycobacterial infections in the differential for patients with persistent cutaneous lesions with known risk factors (immunosuppression, chronic venous stasis, prior trauma). This case also highlights the utility of PCR as a valuable diagnostic technique when histopathologic features on a biopsy are non-specific, and cultures are negative.

AUTHORS:
Elen Deng, BS¹, Mary Helene², Bansri M Patel, MD³, Jeffrey Miller, MD³, Thomas N Helm, MD³

AFFILIATIONS:
¹Penn State College of Medicine, Hershey, PA 17033
²University of South Alabama, Mobile, AL 36688
³Penn State Health, Department of Dermatology, Hershey, PA 17033

CITATION:
Deng E, Helene M, Patel BM, Miller J, Helm TN.  Mycobacterium Chelonae infection diagnosed by PCR in a patient with chronic leg nodules. Consultant. Published online December 29, 2025. doi: 10.25270/con.2025.12.000004
Received August 5, 2025. Accepted October 2, 2025.

DISCLOSURES:
The authors report no relevant financial relationships.

ACKNOWLEDGEMENTS:
None.

CORRESPONDENCE:
Elen Deng, BS, Penn State College of Medicine, 1850 E Park Ave. State College, PA 16803, (email: edeng@pennstatehealth.psu.edu)

References

1. Bartels CM, Bridges AJ. Rheumatoid vasculitis: vanishing menace or target for new treatments? Curr Rheumatol Rep. 2010;12(6):414-419. doi:10.1007/s11926-010-0130-1
2. Leone P, Prete M, Malerba E, et al. Lupus vasculitis: an overview. Biomedicines. 2021;9(11):1626. doi:10.3390/biomedicines9111626
3. Pérez-Garza DM, Chavez-Alvarez S, Ocampo-Candiani J, Gomez-Flores M. Erythema nodosum: a practical approach and diagnostic algorithm. Am J Clin Dermatol. 2021;22(3):367-378. doi:10.1007/s40257-021-00592-w
4. Subbanna PK, Singh NV, Swaminathan RP. Cutaneous polyarteritis nodosa: a rare isolated cutaneous vasculitis. Indian Dermatol Online J. 2012;3(1):21-24. doi:10.4103/2229-5178.93488
5. Yang K, Li T, Zhu X, Zou Y, Liu D. Erythema induratum of Bazin as an indicative manifestation of cavitary tuberculosis in an adolescent: a case report. BMC Infect Dis. 2021;21(1):747. doi:10.1186/s12879-021-06454-4
6. Akram SM, Rathish B, Saleh D. Mycobacterium chelonae infection. In: StatPearls [Internet]. Treasure Island, FL: StatPearls Publishing; updated August 8, 2023. Accessed December 29, 2025. https://www.ncbi.nlm.nih.gov/books/NBK430806/
7. Uslu U, Böhm O, Heppt F, Sticherling M. Skin and soft tissue infections caused by Mycobacterium chelonae: more common than expected? Acta Derm Venereol. 2019;99(10):889-893. doi:10.2340/00015555-3230
8. Masoumi M, Sakhaee F, Ghazanfari Jajin M, Siadat SD, Fateh A. Cutaneous infection with Mycobacterium chelonae in a patient with multiple sclerosis. IDCases. 2024;38:e02077. doi:10.1016/j.idcr.2024.e02077
9. Chung WK, Kim MS, Kim CH, Lee MW, Choi JH, Moon KC, Koh JK. Cutaneous Mycobacterium chelonae infection presenting as symmetrical plaques on both shins in an immunocompetent patient. Acta Derm Venereol. 2009;89(6):663-664. doi:10.2340/00015555-0693
10. Wang XY, Zhang Y, Liu Y, et al. Treatment of nontuberculous mycobacteria skin infections. Front Pharmacol. 2023;14:1242156. doi:10.3389/fphar.2023.1242156
11. Krock C, Gaer O, André E, et al. Skin infections caused by Mycobacterium chelonae: underestimated, especially in immunocompromised patients. JEADV Clin Pract. 2024;4:262-268. doi:10.1002/jvc2.575
12. Gaudêncio M, Teixeira F, Vieira R, et al. Mycobacterium chelonae cutaneous infection: a challenge for an internist. Eur J Case Rep Intern Med. 2021;8(11):003013. doi:10.12890/2021_003013

©2025 HMP Global. All Rights Reserved.
Any views and opinions expressed are those of the author(s) and/or participants and do not necessarily reflect the views, policy, or position of Consultant360 or HMP Global, their employees, and affiliates.