Multiple myeloma presenting with an acute bacterial infection.

Increased susceptibility to bacterial infections is a common manifestation of multiple myeloma (MM), arising mainly from a defect in humoral immunity and is associated with major morbidity and mortality. The propensity to infection is increased in the first months after the initial diagnosis and in patients with renal dysfunction. Gram-positive infections, mainly pneumonia from Streptococcus pneumoniae, occur more frequently in patients with untreated disease while Gram-negative infections, mainly of the urinary tract, are more common after chemotherapy. However, an acute bacterial infection is rarely reported as the first manifestation of underlying MM. In this review, we analysed data from 17 such cases reported between 1978 and 2008. Median age was 65.5 years and most patients were females; monoclonal paraprotein was IgG in 92%. In contrast to diagnosed treated or untreated MM, musculoskeletal infections predominated in these early cases (47%) followed by pneumonia (29%). In particular, septic arthritis, mainly of the knee, was the most common infectious complication (35%). Streptococcus pneumoniae was isolated in two-thirds of infections and bacteremia was common (80%). In this early phase, immunodeficiency arised from a decreased synthesis of polyclonal immunoglobulins. White blood cell counts were frequently normal, particularly in musculoskeletal infections. Renal impairment occurred in 67% and correlated with increasing monoclonal paraprotein levels. The outcome was favorable in most cases (79%). MM should be considered in previously asymptomatic middle-aged patients who present with a major acute bacterial infection, without an apparent predisposing factor. In particular, suspicion should be high in cases of septic arthritis and pneumococcaemia.