Large Spontaneous Subcutaneous Abscess Formation due to Finegoldia magna in a Diabetic Patient: A Case Report

Begaj et al. [1] described that Finegoldia magna which was previously named as Peptostreptococcus magnus is a member of the Gram-positive anaerobic cocci group (GPAC) and constitutes the flora of the skin, gastrointestinal tract, and birth canal. Murphy and Frick [2] also described that it typically colonizes diabetic foot; therefore, a close relationship of the bacterium with diabetic wounds has been suggested. Murphy and Frick [2] reported that F. magna is one of the most virulent GPACs, accounting for 7.5% of all GPAC-infected patients. Begaj et al. [1] revealed that the bacterium commonly targets the skin, soft tissue, and vagina. Neumann et al. [3] described that F. magna frequently forms biofilm and sometimes causes soft tissue abscesses. When reviewing previous reports [1, 4‒12], both necrotizing fasciitis and subcutaneous abscess are major clinical manifestations of infectious disease due to F. magna in the skin and soft tissue. Skin and soft tissue bacterial infectious disease is clinically evaluated with a laboratory risk indicator for necrotizing fasciitis score to diagnose necrotizing fasciitis among various soft tissue infectious diseases. However, Begaj et al. [1] revealed that it can be used as an adjunct to aid clinical decision making in equivocal cases. The clinical manifestation of subcutaneous abscess in previous reports [4, 5] was a nodule of at least several centimeters in diameter. We report a case of a large mass consisting of a severe subcutaneous abscess caused by F. magna on the back of a diabetic patient.

A 48-year-old woman with diabetes mellitus and anemia associated with uterine fibroids was referred to us with a 1-month history of a mass on her back. At that time, she had pain and swelling on her back. The patient had no family member who suffered from cutaneous disorders including infectious disease. The patient had been a close contact of coronavirus infectious disease in 2019 (COVID-19) during the course of the skin disease, resulting in a delayed consultation for the skin disease. The mass grew larger during the 1-month period. Physical examination at the first visit showed a body temperature of 35.9°C and blood pressure of 115/73 mm Hg. A subcutaneous mass of 36 × 45 cm on the back with tenderness, induration, a foul odor, and erythema around it was present. It was partially covered with necrotic tissue with the appearance of a tortoiseshell-like pattern (Fig. 1). Blood examination revealed: white blood cell count, 13,900/µL; hemoglobin, 4.7 g/dL; C-reactive protein, 21.4 mg/dL; sodium, 138 mmol/L; creatinine, 0.57 mg/dL; glucose, 187 mg/dL; and hemoglobin, A1c 9.1%, resulting in a laboratory risk indicator for necrotizing fasciitis score of 7. Bleeding from uterine fibroids and chronic inflammation from subcutaneous mass led to anemia. Contrast-enhanced computed tomography showed an encapsulated hypodense mass of 28 × 32 cm in the subcutaneous fatty tissue of the back with dark low attenuation areas which was potentially regarded as emphysema. There was no involvement in any other organs. An enhancement effect was evident around the mass (Fig. 2). Based on the above findings, the diagnosis of a subcutaneous abscess was made, the abscess was drained, and the upper skin of the abscess was excised under general anesthesia. During the drainage, longitudinal incision was made in the center of the necrotic tissue on the back, and the subcutaneous abscess was opened. After the manual removal of the purulent fluid, the remaining upper skin of the abscess was excised. Infiltration of inflammation into the muscle layer was not observed, and necrotizing fasciitis was ruled out. Bacterial culture of the pus and tissue collected intraoperatively revealed F. magna and Peptoniphilus harei in the pus and F. magna in the skin tissue by using brucella agar with hemin and vitamin K1. The result of blood culture was negative. We considered this case as a severe skin and soft tissue infectious disease. Therefore, broad-spectrum antimicrobial agents were empirically administered as the initial therapy. Intravenous infusions of meropenem at 3 g/day, clindamycin at 1,800 mg/day, and teicoplanin at 600–1,600 mg/day were empirically performed after the drainage. From the 2nd day, topical application of purified white sugar and povidone-iodine and trafermin after wound washing with saline solution was performed every day. Red granulation tissue appeared from the bottom of the wound ulcer, and necrotic tissue decreased day by day. On the 9th day, drug susceptibility test showed that F. magna had a resistance to ampicillin and gentamicin and a sensitivity to oxacillin, cefazolin, cefdinir, flomoxef, imipenem, erythromycin, clindamycin, minocycline, teicoplanin, and fosfomycin. We changed the empirically administered drugs to intravenous cefmetazole because drug susceptibility test showed that F. magna had a sensitivity to cephems antibiotics and it was an available option for us. On the 28th day, we changed the antibiotic to oral minocycline, a sensitive agent, because the inflammation decreased. The patient underwent segmental skin grafting on the 78th day to reconstitute the skin defect. The graft was taken from posterior region of left thigh. Antibiotics were administered until 83rd day. The patient showed a good postoperative course, and epithelialization was confirmed on the 106th day. After the epithelialization, we observed every 3 months, and there are no signs of infection and detachment of the skin graft (Fig. 3).

Bacterial culture in the present case revealed F. magna and P. harei, a Gram-positive anaerobic coccus, in the pus and F. magna in the skin tissue. We thought that F. magna is a causative agent of this infection because (i) only F. magna was detected from viable skin tissue which is supposed to be sterile as well as pus and (ii) five cases suffering from subcutaneous abscess were reported as a F. magna-infectious disease (Table 1).

Begaj et al. [1] described that F. magna is a member of the Gram-positive anaerobic cocci group (GPAC) and constitutes the flora of the skin, gastrointestinal tract, and birth canal. The relationship of F. magna to skin infectious diseases has been indicated. To the best of our knowledge, 12 cases [1, 4‒14] of among F. magna which was previously named as Peptostreptococcus magnus skin and soft tissue infectious diseases with clearly described comorbidities have been reported (Table 1). Diabetes mellitus was the most common condition coexisting with the infectious disease; indeed, diabetes mellitus was present in 8 of 13 patients, including our case. Murphy and Frick [2] reported that F. magna was detected in 23 of 40 patients with diabetic foot ulcer. These results suggest that diabetic patients are more likely to carry F. magna and be more susceptible to skin and soft tissue infectious disease caused by it. Among 7 reports to describe gas production, 5 cases showed gas picture including our case. Therefore, this may be one of the clinical features of F. magna infection.

Including our case, 6 cases [4, 5, 10‒12] of subcutaneous abscess have been reported. Surgical drainage of the abscess was performed in almost all cases, and antibiotic therapy was administered in the majority. All of them were survived as is the case with our patient. Only one death case [7] has been reported, and the patient was suffered from necrotizing fasciitis. It is difficult to discuss the survival rate because the study examined only 13 patients including 1 case with dead outcome.

Culture examination detected P. harei in the pus in the present case. Despite this, we considered that P. harei was not associated with the present infectious disease. The reasons were as follows: (i) the bacterium was not detected in the affected skin tissue by culture examination, and (ii) infectious disease caused by F. magna involved a single causative bacterium in 7 of 13 cases. Based on these factors, the present disease may have been caused by a single infection of F. magna.

The present case showed a significantly large mass consisting of an abscess. It is unusual compared with a subcutaneous abscess in previous reports. The potential reasons are that (i) the bacterium grows relatively slowly as a subcutaneous abscess, (ii) the patient was not able to consult the hospital because she had been a close contact of COVID-19 infection, and (iii) diabetic neuropathy potentially reduced any unpleasant sensation. The present case followed a natural clinical course for a prolonged period. The observation showed that the abscess caused by the bacterium may grow to a marked size.

A broad-spectrum antimicrobial agent is commonly administered as initial therapy for severe skin and soft tissue infectious diseases, and de-escalation should be considered once the causative organism is identified. Although Murphy and Frick [2] reported that F. magna is generally susceptible to penicillin and metronidazole, Shetty et al. [15] described that a small proportion of the strain exhibits penicillin-resistance. The present patient was empirically treated with a combination of meropenem, teicoplanin, and clindamycin at the early days, and the treatment was de-escalated to cefmetazole after confirming drug susceptibility.

The present patient was treated with surgical debridement in addition to antimicrobial therapy. Also, surgical debridement was performed in 12 of 13 cases that we reviewed. Among the 13 reviewed cases, a gas picture was detected in 5 out of 7 cases examined with an imaging device, and necrotizing fasciitis appeared as the infectious disease caused by Finegoldia manga in 5 cases. Considering that (i) both gas-producing skin and soft tissue infectious diseases and necrotizing fasciitis require surgical debridement and (ii) Neumann et al. [3] described that F. magna infection is potentially associated with biofilm formation, surgery is regarded as a standard treatment for severe F. magna infection of soft tissue.

The present case provides valuable insights into the infection caused by F. manga in an immunocompromised patient. Despite it, this study reports only 13 cases of F. Manga infectious diseases and lacks the images of gram staining and the results of minimum inhibitory concentrations against antibiotics, possibly making it difficult to generalize the findings to a larger population. Therefore, further case reports of skin and soft tissue infectious diseases caused by F. manga are needed.

We report a case of F. magna infection appearing as a severe abscess on the back. A close association between F. magna infection and diabetes mellitus was suggested. Skin and soft tissue infectious disease caused by F. magna is rare but severe. Therefore, physicians need to be cautious regarding F. magna infection of poorly controlled diabetic patients. The CARE Checklist has been completed by the authors for this case report, attached as online supplementary material (for all online suppl. material, see https://doi.org/10.1159/000540636).

Ethical approval is not required for this study in accordance with local or national guidelines. Written informed consent was obtained from the patient to publish this report in accordance with the journal’s patient consent policy.

The authors have no conflicts of interest to declare.

The authors received no extramural financial support.

Toshiyuki Sato: conceptualization, data curation, and original draft writing; Mayuka Tomita, Atsuhiro Kohno, Satomi Chujo, Yuma Waki, and Masaaki Kawase: data curation; Yoshimasa Nobeyama: conceptualization, review, and editing; and Akihiko Asahina: supervision.

All the data generated or analyzed during this case report are included in this article and its online supplementary material files. Further inquiries can be directed to the corresponding author.