[Primary meningococcal B osteomyelitis and arthritis with multifocal pyomyositis in a child: a case report].

Neisseria meningitidis is associated with severe invasive infections such as meningitis and fulminant septicemia. Septic arthritis due to N. meningitidis is rare and bone infections have been reported exceptionally. We report the case of a 7-year-old boy who presented with septic arthritis of the right hip associated with a septic location on the pelvis and pyomyositis of the adjacent muscle. Culture of the joint fluid was sterile but universal 16S polymerase chain reaction (PCR) of this fluid revealed group B N. meningitidis. Our patient had never presented any symptoms of meningitis or septicemia and blood cultures were all sterile. Despite appropriate antibiotic treatment, the course of the disease was unusually long and his status did not improve until surgical lavage of the hip was performed. Moreover, MRI imaging showed bilateral hypersignals of the adjacent muscles and revealed an abscess formation in the left gluteus maximus muscle. Presumptive diagnosis bacterial myositis was confirmed by an elevation of creatine phosphokinase in the sera up to 21-fold the normal value but the culture of the abscess, performed 10 days after initiation of antibiotics, was sterile. Despite an initially unfavorable course, this patient's status improved after surgical drainage and he fully recovered 1 month later. This observation illustrates an unusual presentation of invasive meningococcal infection. The respective roles of infection and an inflammatory phenomenon during the course of the disease are discussed. Moreover, this case emphasizes the value of PCR for bacteriological diagnosis of bone and joint infections.