A Case of Pyogenic Vertebral Osteomyelitis and Iliopsoas Abscess Caused by Invasive Pneumococcal Disease Serotype 35F: Utility of Diffusion-Weighted Whole-Body Imaging With Background Body Signal Suppression as an Adjunctive Diagnostic Tool.

We present a case of invasive pneumococcal disease (IPD) complicated by both iliopsoas abscess and pyogenic vertebral osteomyelitis caused by serotype 35F Streptococcus pneumoniae in a 64-year-old man with a history of splenectomy who was unvaccinated. The patient experienced difficulty moving, severe back pain, vomiting, and high fever. Advanced imaging techniques, including T2-weighted lumbar MRI and diffusion-weighted whole-body imaging with background body signal suppression (DWIBS), revealed hyperintensities in the left iliopsoas muscle and L4-L5 vertebral bodies, facilitating diagnosis. Blood cultures confirmed the presence of serotype 35F S. pneumoniae, a non-vaccine type associated with an increased risk of invasive disease and mortality. The patient was successfully treated with targeted antibiotics and disc lavage, resulting in symptom resolution. To our knowledge, this is the first reported case of serotype 35F S. pneumoniae causing both iliopsoas abscess and vertebral osteomyelitis, making it a noteworthy contribution to medical literature. Notably, DWIBS proved to be a valuable adjunct diagnostic tool, highlighting its potential for visually accessible, comprehensive screening of inflammation and abscesses throughout the body. We believe that DWIBS is particularly useful when bacteria capable of inducing lesions in multiple organs, such as S. pneumoniae or Staphylococcus aureus, are isolated from blood cultures. Although DWIBS is still emerging in infectious disease diagnostics, this case underscores its promising role in detecting abscesses and inflammatory lesions.