The growing awareness of pediatricians and the use of organism-specific real-time polymerase chain reaction (PCR) assays, along with other modern techniques of culturing, have markedly improved the detection rate of Kingella kingae infection. In recent years, it has become a commonly detectable pathogen in cases of bacteremia, osteomyelitis and septic arthritis among young children. Other, less common presentations of K. kingae in term of severity and localization have also been described.1,2 We report an atypical, rare, tumor mimicking presentation of K. kingae, stressing the need for considering the diagnosis, especially in young infants.
An 11-month-old, previously healthy, well-nourished and routinely vaccinated male infant was referred from another hospital for further evaluation of a chest wall mass. Three days earlier, his mother had noticed an abrupt swelling on his right chest without fever or any accompanying symptoms other than coryza in the past several days. He had no history of blunt trauma to the chest, and had no exposure to animals.
On admission to the first hospital, the patient underwent ultrasonographic imaging of the chest wall, which revealed a hypoechogenic parasternal mass with undefined borders, measuring approximately 1 x 3 cm, infiltrating the adjacent subcutaneous fat without involvement of the ribs. Computed tomography scan demonstrated a homogeneous mass at the inferior part of the right anterior chest (2.5 x 4.4 cm), involving subcutaneous fat and muscles surrounding the rib cartilage (see Fig., Supplemental Digital Content 1, http://links.lww.com/INF/C549). Laboratory data showed normal blood count, biochemistry and clotting function. He was then transferred to our hospital for further evaluation.
Physical examination on admission showed a well-appearing infant with no signs of any distress. His vital signs were normal, including body temperature. Chest physical examination revealed a hard, nonfluctuating mass (3 x 3 cm; see Fig., Supplemental Digital Content 2, http://links.lww.com/INF/C550). Laboratory data showed a white blood cell count of 7890 cells/μL with moderate neutropenia of 950 cells/μL and atypical lymphocytes of 25%, hemoglobin 11.7g/dL, platelet count of 362 cells/μL, C-reactive protein of 10 mg/L and sterile blood culture. The infant was hospitalized for further evaluation with the suspicion of a tumor and underwent another ultrasonography (see Fig., Supplemental Digital Content 3, http://links.lww.com/INF/C551) and a fine needle biopsy.
The biopsy was sent to pathology and microbiology laboratories. Pathology results showed an acute or chronic mononuclear inflammation with no signs of malignancy. Considering this result, and taking into account the diagnosis of presumed osteomyelitis, antibiotic therapy with first generation cephalosporins was started while waiting for the culture and PCR results. Serology for Q-fever was negative. Clinical improvement was observed while receiving antibiotic treatment. The results of microbiology were sterile for aerobic and anaerobic cultures, negative Ziehl–Neelsen stain, with a later sterile culture for mycobacterium. The panbacterial 16SrRNA PCR was positive for K. kingae.
The infant was discharged after 1 week with remarkable improvement in the lump dimensions. Based on the microbiologic results and the tomography findings, the infant was diagnosed as having osteomyelitis of the ribs and deep tissue infection, and overall treatment duration was expected to be 6 weeks. On follow-up visits, the chest mass gradually diminished until full recovery.
Kingella kingae is a facultative anaerobic, β-hemolytic, Gram-negative organism. It has become a common etiology of pediatric osteoarticular infections, especially in children younger than 5 years of age, with less common manifestations of bacteremia and endocarditis. The increase in reported cases may be related to better knowledge about the organism, improved culture methods and the use of nucleic acid amplification techniques in clinical microbiologic laboratories.1,3 Most patients with invasive K. kingae infection have moderate fever, but some are afebrile, a fact that can cause a delayed diagnosis. Constitutional symptoms are typically lacking except in patients with endocarditis. Peripheral white blood cell count, C-reactive protein value and erythrocyte sedimentation rate are generally mildly to moderately elevated but can be normal.3 Almost 90% of invasive K. kingae infections occur in children aged <5 years, and 60% in those aged <2 years.4 As in the case of septic arthritis caused by other microorganisms, K. kingae arthritis occurs mainly in the large weight-bearing joints, such as the knee, hip and ankle,3,4 and less frequently in the wrist, shoulder, elbow, metacarpophalangeal, sterno-clavicular and tarsal joints.4 A rarer presentation in children is endocarditis, which is considered the most severe form of K. kingae infections and is accompanied by a very high rate of neurologic complications. Children with K. kingae endocarditis are usually older than those with osteoarticular infections (mean 25 vs. 15 months) and present with higher fevers and acute phase reactant values as described by Dubnov-Raz et al.5
In our report, we describe a K. kingae infection presenting as a tumor-like mass with rare involvement of ribs and soft tissue. Kingella kingae chest wall infection has been previously described with involvement of the lower sternum and manubrium–xyphoid junction in 7 cases in the English literature.6,7Table 1 represents a summary of all cases including our case. In the majority of these cases, patient ages ranged from 10 to 15 months, clinical signs were usually mild, body temperatures were mostly normal and acute phase reactants were moderately elevated. BACTEC blood cultures were not a satisfactory method for diagnosis, and there was a need for specific PCR.6,7
The uniqueness of our report is in describing the first case of osteomyelitis of the ribs in an infant with accompanying soft tissue chest infection. Due to the lack of constitutional symptoms and acute phase reactant, and the aggressive invasion of the mass to adjacent ribs and soft tissue, the chest finding was confused with a malignant lesion.
The extensive differential diagnosis of such a rare sternal mass in children and infants can be divided into a malignant or benign tumor, infectious process or aseptic inflammation called “self-limiting sternal tumor of childhood,” which is characterized by its well-defined sonographic appearance.8
The adequate management of bone and joints infection requires the identification of the causative microorganisms to determine the appropriate antibiotic therapy. However, this may be difficult when antibiotics are administered before sampling or when fastidious microorganisms like K. kingae are involved.9
Despite the progress in culturing methods and the use of BACTEC for blood cultures, kingella isolation from blood or synovial fluid is still challenging with a detection rate of approximately 40%.10 Molecular methods have been developed recently to detect causative pathogens in culture-negative synovial fluids. Broad-range 16S rRNA PCR has succeeded in detecting the organism in 9% of culture-negative synovial fluids incubated for 6 days.9 Discrepancies between culture results and PCR were explained by fastidious pathogens, mostly anaerobic species, in adults and K. kingae in children and nonfastidious pathogens, mostly Staphylococcus aureus, recently exposed to antibiotics.9 Based on the high prevalence of K. kingae infection in negative culture arthritis in children, a new real-time PCR method with a highly specific probe for K. kingae was developed, and this method succeeded in identifying K. kingae in 24 of 53 culture-negative synovial fluids. Real-time PCR amplification of drainage fluid samples showed that the pathogen could be detected for up to 6 days after initiation of antibiotic treatment.10
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