CPC06 Cutaneous embolic Rothia mucilaginosa infection in a patient with relapsed acute myeloid leukaemia following allogeneic stem cell transplantation

Abstract

Rothia mucilaginosa is a Gram-positive coccus that forms part of the normal oral and respiratory tract flora. It is an infrequent cause of invasive infection usually reported in severely immunocompromised patients. Cutaneous manifestations are rarely described. A 34-year-old man with a history of acute myeloid leukaemia with trisomy 8 and FLT3 internal tandem duplication mutation underwent allogeneic bone marrow transplantation in early 2023. He relapsed in late 2025 with extramedullary disease involving the left thigh, resulting in a compressive deep-vein thrombosis. During admission, he reported the acute onset of two discrete erythematous lesions over the right pretibial region, present for 24 h. He denied trauma, pain, pruritus or prior similar lesions. At the time of dermatology review, he was pyrexial and receiving broad-spectrum antimicrobials. Examination of the right lower limb revealed two well-demarcated, nontender, circular erythematous lesions measuring 10 × 10 mm over the distal pretibial area and proximal lateral malleolus. Dermoscopy demonstrated scant telangiectasia. Two 4-mm punch biopsies revealed colonies of microorganisms surrounded by granulomatous inflammation with microorganisms in the cytoplasm of macrophages and giant cells, including in a perivascular distribution. Some intravascular organisms were seen in association with fibrin thrombi. Gram staining showed Gram-positive cocci. Rothia mucilaginosa was isolated from both skin biopsy and blood cultures. The lesions were managed as presumed cutaneous embolic deposits with intravenous vancomycin, ceftazidime–avibactam, metronidazole, teicoplanin, and liposomal amphotericin, with clinical improvement. Transthoracic echocardiography demonstrated no evidence of endocarditis. Computed tomography of the thorax was concerning for invasive aspergillosis, with subsequent normal bronchoscopy. This case highlights the importance of maintaining a high index of suspicion for atypical pathogens in profoundly immunocompromised patients. We advocate for prompt biopsy of nonspecific cutaneous lesions in this cohort, as early dermatological assessment can facilitate diagnosis of systemic infection and guide timely management.