Refractory granulomatous lobular mastitis associated with subpectoral abscess and localized Salmonella infection: A case report

Abstract

We report a rare granulomatous lobular mastitis (GLM) associated with Salmonella spp. infection in a 41-year-old woman presenting as a subpectoral abscess. Diagnosis was delayed due to negative routine cultures and atypical presentation. Surgical excision combined with long-term levofloxacin therapy achieved full recovery. Effective treatment requires antimicrobial coverage and elimination of static secretions in the mammary gland to prevent recurrence. Our case presents a unique perspective by illustrating how Salmonella, a facultative intracellular pathogen that targets macrophages and other immune cells, may secondarily infect a GLM lesion, characterized by dense infiltration of immune cells.

Introduction

Granulomatous lobular mastitis (GLM) is a relatively rare, benign inflammatory breast disease first described by Kesseler and Wolloch in 1972.¹ It is characterized by noncaseating granulomas and microabscesses confined to the breast lobule.² The condition presents as a firm mass, which is often indistinguishable from breast cancer, or as multiple or recurrent abscesses. The aetiology remains unclear, but GLM typically occurs in young women, often within 5 years of pregnancy. GLM can be predisposed to hyperprolactinemia, as the breast ducts and lobules are filled with thick content, which causes obstruction associated with static secretions that may either become infected or escape into the perilobular stroma, leading to a T-cell-mediated immune response and the formation of granulomas. Indeed, several infectious agents have been identified in patients with GLM, most notably Corynebacterium spp., particularly C. kroppenstedtii.^3,4

Here, we report a rare case of GLM with a subpectoral abscess in a 41-year-old woman, ultimately diagnosed as a localized Salmonella spp. infection.

Case report

A 41-year-old woman with no significant medical history developed pain radiating from her left breast to the back, breast swelling, and fever one month postpartum. She was diagnosed with mastitis at a local hospital, where ultrasonography revealed a subpectoral abscess. No pathogens were identified from the aspirated fluid. She was treated with a cephalosporin antibiotic for six weeks, resulting in symptom resolution.

Three years later, she experienced recurrent left breast pain. A contrast-enhanced CT performed at a local clinic revealed an intramuscular abscess of the pectoralis major. Despite oral faropenem therapy, her symptoms recurred, and she was referred to our breast surgical department three months later. A drain was inserted into the abscess cavity under fluoroscopic guidance, yielding no pathogenic organisms. Daily saline irrigation was performed for two weeks, with symptomatic improvement.

One month later, the patient developed breast induration and tenderness. A contrast-enhanced chest CT revealed a cystic mass extending from the mammary gland in the lower inner region of the left breast to the subpectoral area (Figure 1). She was referred to our department for further evaluation. On physical examination, induration and tenderness were noted in the lower inner quadrant of the left breast. MRI revealed a high signal intensity on fat-suppressed T2-weighted imaging, suggesting fluid collection extending from beneath the left mammary gland to the subpectoral region.

Figure 1.

A contrast-enhanced chest CT revealed a cystic mass extending from the mammary gland in the lower inner region of the left breast to the subpectoral area.

Three weeks after referral to our department, excision of the indurated lesion in the lower inner quadrant of the left breast and drainage of the subpectoral abscess were performed under general anesthesia (Figure 2). Since the previous drainage site had developed into a cutaneous fistula, gentian violet was injected through the fistula opening. The stained area extended from the mammary gland, penetrating the pectoralis major muscle, and spreading beneath it. The portion of the stained region beneath the pectoralis major that could not be excised en bloc was curetted, and two drains were placed. Postoperative pathological examination demonstrated GLM. Histologically, large epithelioid cell granulomas containing eosinophilic necrotic material were observed between the mammary lobules and the pectoralis major muscle (Figure 3). The granulomas exhibited a stellate configuration extending toward the mammary lobules. Small granulomas were also sporadically found within and between the lobular stroma. Although the preexisting structures were destroyed, the primary site of the lesion was presumed to be the deep mammary tissue. The necrotic material contained a small number of neutrophils and nuclear debris. Numerous foreign body-type multinucleated giant cells were present along the granuloma walls, and a surrounding infiltrate of inflammatory cells, predominantly lymphocytes, was also noted. PAS and Grocott stains showed no evidence of fungal infection. No malignant features were observed, and Ziehl–Neelsen staining was negative for acid-fast bacilli. Initial antibiotic therapy with cefazolin (1 g every 12 h) was started. On postoperative day 4, cultures identified Salmonella spp., and the antibiotic was switched to levofloxacin (500 mg daily). All drains were removed by postoperative day 6. The clinical course remained favorable, and levofloxacin was discontinued on postoperative day 22. However, on postoperative day 25, the patient developed profuse wound exudation, pain along the ribs, localized warmth, and redness of the left breast. Ultrasonography suggested abscess recurrence, and aspiration yielded a small amount of brownish purulent fluid. Suspecting persistent localized infection, levofloxacin was resumed. Contrast-enhanced CT and MRI revealed a small subpectoral abscess and a cutaneous fistula along the drainage tract. By two months postoperatively, breast pain, erythema, swelling, and warmth had resolved. Four months postoperatively, the cutaneous fistula had closed, and the abscess had resolved completely. Approximately one week before the 4-month follow-up, the patient developed vaginal candidiasis, likely due to prolonged antibiotic therapy. As a result, she discontinued levofloxacin on her own, and the medication was not resumed thereafter.

Figure 2.

An anterior view of the lower inner quadrant of the left breast during the surgery. A portion of the nipple is visible in the upper right corner. a) Indurated lesion and abscess wall immediately before excision. b) After excision of the indurated lesion and abscess wall. The cut edge of the pectoralis major and underlying structures, such as the perichondrium of the costal cartilage, are exposed.

Figure 3.

The histopathology slide showed chronic inflammation with large epithelioid cell granulomas (arrowheads) located between the mammary lobules (asterisks) and the pectoralis major muscle (arrows), containing eosinophilic necrotic material.

Discussion

This case presented recurrent episodes of mastitis and abscess formation over an extended period, during which no causative pathogen could be identified. These features complicated both diagnosis and treatment. Ultimately, the patient was diagnosed with GLM associated with Salmonella spp. infection. Complete resolution was achieved through surgical excision of the GLM, drainage, and long-term administration of levofloxacin.

Recent literature suggests a correlation between GLM and C. kroppenstedtii, a lipophilic organism that favors fatty tissue such as the breast. Salmonella spp. was identified in this case as an exceptionally rare cause of GLM. GLM associated with Salmonella was first reported by Alsaket et al. in 2023 and remains extremely uncommon.⁴ Salmonella was not readily detected in the present case, and repeated culture tests were required. This may be attributed to the possibility that the strain belonged to a serotype such as S. Dublin (bovine adapted) or Salmonella choleraesuis (porcine adapted), which are known to be highly host-adapted and auxotrophs.⁵ However, in this case, the Salmonella spp. was detected without specialized culture media. Therefore, it may be more reasonable to consider that the T-cell-mediated immune response and subsequent granuloma formation induced by static secretions in the mammary gland preceded the secondary Salmonella infection. Taylor et al.³ proposed that excisional surgery may be effective in many cases of GLM, and for the same reason, it is effective in patients with duct ectasia. Static secretions are a significant problem in both groups. The persistence of static secretions as a potential substrate for infection may be why antibiotics are frequently ineffective.

Salmonella spp. are pathogenic Gram-negative, rod-shaped, motile bacteria belonging to the Enterobacteriaceae.⁶ Salmonella invades microfold cells and is taken up by dendritic cells from the intestinal lumen. Salmonella-induced cell death and subsequent phagocytosis could facilitate access to other cell types.⁷ Target cells include macrophages, monocytes, neutrophils, B cells, and T cells. Salmonella can disseminate to internal organs because it is a facultative intracellular pathogen that usually resides in a modified phagolysosome known as the Salmonella-containing vacuole that does not fuse with lysosomes during host infection.⁸ Fluoroquinolones are effective against Salmonella because they exhibit bactericidal activity against intracellular pathogens.⁵

Although the Salmonella infection in our case was most likely secondary, the immunopathological context of GLM may have facilitated this rare site of dissemination. GLM is increasingly understood as an autoimmune-related disease,⁹ characterized by chronic granulomatous inflammation and infiltration by immune cells, particularly macrophages. Salmonella spp. preferentially infect phagocytic cells, making inflamed, immune-rich environments, such as GLM lesions, potential targets for infections. Salmonella typically disseminates to the internal organs of the mononuclear phagocyte system, such as the mesenteric lymph nodes, liver, and spleen, where immune surveillance is concentrated.⁶ Spread to other organs—including the breast—is rare. Thus, this case highlights a plausible mechanism of immune cell–mediated secondary infection in GLM and illustrates the importance of maintaining vigilance for infectious complications during treatment.

Considering that three years elapsed between the resolution of the initial episode of GLM and its recurrence, long-term follow-up is essential. Furthermore, even if recurrence occurs in the future, it remains uncertain whether Salmonella infection will be involved again.

Conclusion

This case highlights the diagnostic and therapeutic challenges of GLM associated with rare pathogens such as Salmonella spp. Surgical excision combined with prolonged antibiotic therapy can achieve complete resolution. Our report offers a unique perspective by illustrating how Salmonella, a facultative intracellular pathogen that targets macrophages and other immune cells, may secondarily infect GLM lesions characterized by dense infiltration of immune cells.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.