Actinomycosis by schaalia odontolytica masquerading as a mediastinal mass in an immunosuppressed patient

SESSION TITLE: Chest Infections in Immunocompromised Individuals SESSION TYPE: Rapid Fire Case Reports PRESENTED ON: 10/10/2023 09:40 am - 10:25 am INTRODUCTION: Actinomycosis is a rare endogenous infection characterized by indolent progression, contiguous spreading, abscess formation, and draining sinuses. Here, we present a unique case of acute actinomycosis caused by Schaalia odontolytica manifesting as a mediastinal mass. CASE PRESENTATION: A 65-year-old female with a medical history of diabetes, kidney transplant, and long-term immunosuppression presented with dysphagia and odynophagia for 3 weeks. She had a nonrevealing chest computed tomography (CT) for other reasons several days before the symptom onset; however, a repeat CT scan 1 week later revealed a soft-tissue density upper mediastinal mass measuring 2x5x6 cm, anteriorly displacing the esophagus (Figure 1, 2). An upper endoscopic ultrasound (EUS) showed no intraluminal esophageal lesion or ultrasonographic evidence of mass invasion to the adjacent tissue. An EUS-guided fine needle aspiration yielded purulent material. The fluid analysis revealed a single colony of Schaalia odontolytica on culture but no malignancy cell on cytology.Mediastinal actinomycosis was diagnosed, and empiric intravenous ceftriaxone (2g daily) treatment commenced. Despite the therapy, the patient's swallowing symptoms worsened with a new onset cough, prompting an urgent video-assisted thoracoscopy for abscess incision and drainage. Intraoperatively, resolution of the external esophageal compression was observed from an endoscope. The patient continued receiving ceftriaxone for 7 weeks until a CT scan confirmed abscess resolution, followed by another 3 months of oral amoxicillin (1g twice daily, renally dosed). At a 5-month follow-up, she had returned to her baseline health state with no complaints. DISCUSSION: Thoracic cases constitute 15% of all actinomycoses, (1) but mediastinal involvement is rarely described in the literature and is usually associated with medical devices such as esophageal stents. Unlike the typical indolent course, this patient's large abscess formed within a week. The rapidity of abscess enlargement was attributed to her underlying diabetes and chronic immunosuppression.In over 98% of the cases, the causative organisms are within the Actinomyces genus. Schaalia odontolytica, previously known as Actinomyces odontolyticus, was re-described as the type species of the new Schaalia genus under the family Actinomycetaceae. (2) It shares similar microbiologic and clinical characteristics with A. israelii, the most common cause of actinomycosis.Diagnosis of actinomycosis can be challenging, as cultures are negative in up to half of the cases. Presumptive diagnosis often relies on tissue exams and clinical data such as "Sulfur" granules and imaging findings. Regarding treatment, penicillin G is the drug of choice but may be limited by availability or allergy (as in this case). Other antibiotics, including aminopenicillin with or without a beta-lactamase inhibitor, third-generation cephalosporins, carbapenems, quinolones, and macrolides, have been shown effective. A median antibiotic duration of 5.3 months was reported, and over 1/5 of patients received surgery as part of initial management. (3) CONCLUSIONS: We report a case of actinomycosis with a very unusual location, acuity, and causative bacterium. Mediastinal involvement renders a low threshold for surgical intervention and prolonged antimicrobial therapy. REFERENCE #1: Cardoso CG, Freitas C, Gomes I, et al. Enlightening clinical and therapeutic heterogeneity in thoracic actinomycosis: A review in bronchiectasis and non-bronchiectasis patients. Pulm Pharmacol Ther 2021;71:102078. PMID: 34571094 REFERENCE #2: Nouioui I, Carro L, García-López M, et al. Genome-Based Taxonomic Classification of the Phylum Actinobacteria. Front Microbiol 2018;9:2007. PMID: 30186281 REFERENCE #3: Park JY, Lee T, Lee H, et al. Multivariate analysis of prognostic factors in patients with pulmonary actinomycosis. BMC Infect Dis 2014;14:10. PMID: 24400792 DISCLOSURES: No relevant relationships by Emad Abu Sitta No relevant relationships by Ibrahim Ahmed No relevant relationships by Jiannan Huang No relevant relationships by Dawlat Khan