Unmasking disseminated streptococcal infection: role of FDG PET/CT in diagnosis and assessing response to antibiotic treatment

Excerpt

A 37-year-old man was treated with surgery and chemo-radiation therapy for carcinoma of the left buccal-mucosa. He underwent left marginal mandibulectomy after raising a cheek flap and left neck dissection in October 2020 followed by external beam radiation therapy to face and neck (60 Gy in 30 fractions, 6 MV photon) for 6 weeks using intensity-modulated radiation therapy technique along with 6 cycles of concurrent cisplatin chemotherapy (treatment ending in January 2021). He presented 4 months later (May 2021) with complaints of pus draining from the operated site in the left cheek and fever of 2-week duration. Surgical site infection was considered on the basis of patients symptoms, and clinical examination and laboratory tests like ESR and CRP were not done. However a FDG PET/CT was performed to rule out the possibility of underlying co-existing disease recurrence. Imaging showed low-grade diffuse FDG uptake in the skin and subcutaneous region at operated site (arrowhead in A). There was no focal FDG uptake or enhancing soft tissue to suggest the possibility of local recurrence (arrow in B), and FDG avid lymphadenopathy and marrow lesions were noted at multiple distant sites (Fig. 1A, C, and D arrows). Pus swab from discharging sinus revealed heavy growth of streptococci. On the basis of patient’s history, clinical, microbiological, and imaging findings disease recurrence was ruled out and a diagnosis of disseminated streptococcal infection was made. A course of oral antibiotic therapy (amoxicillin + clavulanate) was prescribed to the patient. Follow-up imaging after 12 weeks of antibiotic therapy showed complete resolution of metabolism at the site of pus discharge in the cheek as well as the disseminated sites of nodal and marrow involvement (Fig. 1E–H). There was no evidence of recurrence of malignant disease. Streptococcus is a gram-positive cocci which can be a common cause of infection after a surgical procedure [1].

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