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Journal of Medical Cases

Case Report

Volume 6, Number 8, August 2015, pages 339-341

Isolated Mediastinal Kocuria rosea Infection Mimicking Malignancies

Enlarged lymph nodes in the mediastinum can be due to neoplasia infection or other diseases and the classification of these nodes is crucial to correct management of such a patient [1]. Advances in imaging of mediastinal lymph nodes (MLNs) with 18-fluoredeoxyglucose position emission tomography and computed tomography (18FDG PET/CT) have improved diagnostic accuracy and determination of nodal status. However, due to the low specificity of PET positive MLNs should be biopsied to confirm or rule out metastasis and invasive surgical diagnostic techniques such as mediastinoscopy are the preferred biopsy methods of obtaining MLN tissue.

Kocuria rosea, an aerobic Gram-positive coccus is generally regarded as a non-pathogenic commensal that colonizes the oropharynx, skin, and mucosa. Nonetheless, it is capable of causing opportunistic infection in immunocompromised patients [2].

We report the case of PET positive, necrotizing MLN associated with Kocuria rosea in an otherwise healthy young man. Only a limited number of Kocuria rosea infections are reported in the literature and ours seems to be only the second published case and the first in which diagnosis and treatment have been carried out by mediastinoscopy.

We report the case of a young adult male who presented with mediastinal lymphadenitis in the absence of commonly associated features: no compromised immunity or HIV-infection, no signs or symptoms of infection or mediastinum involvement, and a rapid response to therapy. In addition, the patient reported no symptoms of upper respiratory tract infection, had no palpable lymph nodes or no fever. Additionally, all laboratory results, including blood count, biochemical findings, and C-reactive protein, were within normal range. A PET/CT was performed, and abnormal 18FDG uptake was apparent around the area of tracheal bifurcation. The standardized uptake value (SUV max) was 8.9 (Fig. 1). A mediastinal lymphadenectomy was performed, and histological lymph node analysis confirmed necrotizing lymphadenitis. Microbiological diagnosis of the tissue was performed and culture positive for Kocuria rosea was obtained. Antibiotic sensitivity tests were not performed and 3 days after admission, the patient was discharged from the hospital in good condition.

Click for large image

Figure 1. PET/CT showed a swollen mediastinal lymph node measuring 10 mm in diameter at the tracheal bifurcation.

Kocuria is a member of the Micrococcaceae family, which presently comprises 18 species [3]. Although generally regarded as harmless saprophytes that inhabit or colonize skin and oropharynx mucosa this aerobic, non-encapsulated, non-motile bacteria can cause opportunistic infection in the immunocompromised host [3]. Infections such as endocarditis, arthritis, central nervous system infection, pneumonia, peritonitis, hepatic abscess and nosocomial blood stream infections have all being reported [2-4]. In addition, strains identified as Micrococcus spp. have been reported recently in infections associated with indwelling intravenous lines, continuous ambulatory peritoneal dialysis fluids, ventricular shunts and prothetic valves [2-5]. Our case of Kocuria infection is interesting as its unusual presentation made the diagnosis of Kocuria rosea infection very difficult to consider at all.

18FDG PET/CT scanning has been useful in the evaluation of malignant disorders and has been extensively used in cancer screening. However, 18FDG uptake is not specific to cancerous lesions, but is also present in more benign diseases such as infection and inflammation, particularly granulomatous diseases [6]. However, occasionally, a granulomatous isolated necrotizing lymph node presents focal “hot spots”, which can be easily misinterpreted as malignancy. This report emphasizes that granulomatous necrotizing lymph nodes can present a potential pitfall when interpreting FDG scans.

Kocuria rosea infection is rare; it should be considered when FDG PET shows intense FDG uptake in non-regionally swollen lymph nodes.

Acknowledgement

We acknowledge support by the German Research Foundation and the Open Access Publication Funds of the Gottingen University.

Competing Interests

The authors declare that they have no competing interests.

Abbreviations

18FDG PET/CT: 18-fluoredeoxyglucose position emission tomography and computed tomography; MLN: mediastinal lymph node; SUV: standardized uptake value

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