Iliopsoas Abscess Related to Pseudomonas aeruginosa: A Case Report

We describe a rare case of an 80-year-old male with an iliopsoas abscess (IPA) associated with Pseudomonas aeruginosa (P. aeruginosa). The patient had a history of diabetes mellitus and was admitted to our hospital due to aspiration pneumonia, where he was treated with ampicillin/sulbactam (ABPC/SBT). After admission, he experienced a recurrence of aspiration pneumonia, and ABPC/SBT was repeatedly used. The fever resolved by day 30 and antibiotic therapy was completed on day 33. Although the patient remained afebrile thereafter, anorexia persisted. On day 57, the patient experienced chills, fever, lower back pain, and bowel incontinence, leading to the resumption of ABPC/SBT at 6 g/day. Blood tests on day 59 showed elevated lactate dehydrogenase (239 IU/L) and C-reactive protein (15.08 mg/dL), along with decreased red blood cell count, hemoglobin, and albumin. An abdominal CT scan on day 60 indicated a low-density area suggestive of an abscess in the right iliopsoas muscle, and blood cultures from day 57 were positive for P. aeruginosa, prompting a switch to meropenem (MEPM) at 3 g/day. On day 61, lumbar MRI indicated hyperintensity at the L2/3 disc and vertebral bodies, suggestive of discitis and vertebral osteomyelitis. The antibiotic regimen was then changed to ciprofloxacin (CPFX) at 800 mg/day on day 62. Despite ongoing treatment, the patient's fever persisted, and percutaneous and surgical drainage were deemed unfeasible due to the abscess's size and location. The patient experienced a recurrence of pneumonia, leading to a switch to cefepime (CFPM) at 2 g/day on day 86, followed by piperacillin/tazobactam (PIPC/TAZ) at 13.5 g/day on day 96. Due to the deterioration of his clinical condition, he was transferred to a chronic care facility for palliative management on day 102 of hospitalization. Reports of IPA related to P. aeruginosa are very limited. In our case, the patient experienced recurrent pneumonia following hospitalization, and P. aeruginosa was isolated from the blood, suggesting that the lungs were the portal of entry, potentially leading to IPA as a result of the bloodstream infection. In cases involving the combination of P. aeruginosa and IPA, various compromised host factors, along with P. aeruginosa itself, may contribute to adverse outcomes. This report may enhance our understanding of the relationship between IPA and P. aeruginosa infections. Further accumulation of case reports and studies is necessary to better understand future treatment strategies and prognosis for IPA related to P. aeruginosa.