A Case of Invasive Pneumococcal Disease (Serotype 23A) with Septic Arthritis and Pyogenic Discitis Who was Diagnosed Subsequently as Having Multiple Myeloma

<p>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.</p>