In this report, we describe a case of brain abscess due to inadequate treatment based on initial blood culture results because emergency surgical treatment of a severe cerebral hemorrhage was given priority. This case emphasizes the importance of first recognizing bacteremia based on culture results, and if bacteremia is determined to be present, of selecting appropriate antimicrobial agents and ensuring an adequate treatment period.

Multiple myeloma (MM) is a hematologic malignancy of plasma cell origin that increases the susceptibility to bacterial infections, in particular, those caused by encapsulated bacteria like pneumococci. Recently, the incidence of invasive pneumococcal disease (IPD) has decreased, as pneumococcal vaccines have become popular. On the other hand, the incidence of IPD caused by non-vaccine serotypes is reported to have increased. Herein, we describe the case of a 69-year-old man with IPD caused by the 23A serotype of pneumococcus, who was subsequently diagnosed as having MM. He had no history of having received the pneumococcal vaccine. He presented with a history of fever and back pain and developed arthralgia in the left hand and right knee. Blood and joint fluid culture were positive for Streptococcus pneumoniae. The cerebrospinal fluid test for pneumococcal antigen was positive, but there was no pleocytosis. Subsequently, clinical examination revealed evidence of pyogenic discitis. The patient was started on intravenous antibiotic therapy, but the back pain worsened, and hypercalcemia and M-protein positivity were noted. Based on a positive result for Bence-Jones protein, we suspected the diagnosis of MM. Pneumococcus serotype 23A is one of the non-vaccine types of pneumococci, and first appeared in Japan after pneumococcal vaccination became common in Japan. Moreover, infections with the serotype 23A pneumococci are reported to be associated with a significantly increased risk for mortality. MM increases the risk of infections with encapsulated bacteria, because of the impaired cell-mediated immunity, insufficient opsonization activity due to impaired function of complement, and humoral-mediated immunodeficiency. The initial manifestation in some cases of MM is IPD. Since our patient had had no symptoms prior to this episode, it is possible that he had subclinical MM and developed IPD. Among patients with IPD, we should pay attention to intercurrent diagnosis of MM, because the combination of IPD and MM is sometimes life-threatening.