Salmonella-induced Psoas Abscess in a Patient with Multiple Myeloma: A Case Report and Systematic Literature Review

Salmonellosis, caused by the gram-negative bacillus Salmonella, remains a significant infectious disease burden, particularly in low-income countries^[1]. Its clinical spectrum most commonly includes acute gastroenteritis, bacteremia, enteric fever, and asymptomatic carriage. Although focal infections are more typical in immunocompromised individuals, extraintestinal manifestations such as musculoskeletal involvement have also been reported in immunocompetent patients^[2].

A psoas abscess, which is defined as a purulent collection within the iliopsoas muscle of the retroperitoneal space, is most often caused by Staphylococcus aureus^[3]. In contrast, Salmonella-induced psoas abscess is exceptionally rare, with fewer than 40 cases described in the literature^[4-31]. Here, we have presented a unique case of Salmonella psoas abscess in a patient with multiple myeloma in light of a systematic review of published cases.

Case Presentation

A 65-year-old woman with a history of multiple myeloma presented to the emergency department with persistent nausea and vomiting for the past month. On admission, she was in moderate general condition, conscious, oriented, and cooperative. Her vital signs were as follows: temperature 38 °C, blood pressure 110/70 mmHg, pulse 73 bpm, respiratory rate 20 breaths/min, and oxygen saturation 99% on room air. Respiratory examination revealed normal breath sounds, and the abdomen showed no guarding, rebound, or tenderness. Other systemic findings were unremarkable.

Laboratory evaluation demonstrated a white blood cell count of 3.28 × 10³/µL, hemoglobin 7.4 g/dL, platelet count 6 × 10⁹/L, C-reactive protein 216 mg/L, and creatinine 3.5 mg/dL (baseline 2.0 mg/dL). Thoracic computed tomography (CT) revealed a left-sided pleural effusion measuring up to 8 cm in thickness with associated passive atelectasis (Figure 1). Accordingly, she was admitted to the hematology department and transfused with two units of erythrocyte suspension and one unit of platelet concentrate. Blood cultures yielded nontyphoidal Salmonella spp. (identified by MALDI-TOF MS; Bruker Daltonics, Germany; score 2.132), susceptible to fluoroquinolones and cephalosporins (Table 1). For this, intravenous ciprofloxacin (400 mg/day) was initiated.

To investigate the source of infection, abdominal CT was performed, which revealed a 43-mm fluid collection with gas formation in the right psoas muscle (Figure 2). Magnetic resonance (MR) cholangiography further suggested bilateral psoas collections, extending up to 9 cm on coronal T2-weighted images (Figure 3). CT-guided percutaneous drainage of the abscess was accordingly performed, and the culture of the aspirate again grew Salmonella spp. (serovar not identified; MALDI-TOF MS score 2.070). Following the emergence of ciprofloxacin resistance, therapy was switched to ceftriaxone 2 g IV every 12 h (Table 2).

The patient’s history included hospitalization 3 months ago for Salmonella bacteremia after an episode of gastroenteritis, which was treated with a 14-day course of ceftriaxone. At that time, stool cultures were negative, and abdominal imaging showed no abscess formation. During the current admission, her condition progressively deteriorated, requiring transfer to the intensive care unit. Follow-up thoracic CT revealed recurrent pleural effusion (8 cm) and multiple mediastinal lymph nodes. Pleural drainage was performed, though cultures were negative. Ceftriaxone therapy was continued.

Further evaluation for possible spondylodiscitis was planned, but MR imaging (MRI) with contrast could not be performed due to worsening renal function. Positron emission tomography imaging was scheduled; however, the patient’s condition declined further, and she ultimately succumbed to her illness.

Literature Review

A comprehensive literature review was conducted with reference to the PubMed, Scopus, and Web of Science databases, covering studies published from database inception through May 2025. The search strategy employed the keywords “Salmonella” and “psoas abscess” and was restricted to adult patients (age ≥18 years). Only English-language case reports were considered, whereas pediatric cases were excluded.

From the retrieved literature, cases were screened for eligibility based on the availability of summary or full-text data. Extracted variables included demographic characteristics, clinical presentation, underlying risk factors, immune status, culture results, antimicrobial therapy, and clinical outcomes. A total of 33 cases were identified as such, of which 29 adult cases met the inclusion criteria for detailed analysis. An overview of the study selection process and the summarized case characteristics is illustrated in Figure 4.

Salmonella-induced psoas abscess is an exceptionally rare clinical entity. Our review of the English-language literature identified 33 reported cases, of which 29 adult cases with accessible summary or full-text data were analyzed. The mean patient age was 55.4 years, and 72% (n=21) of them were male. The most frequently reported symptoms were fever (65%, n=19), back pain (41%, n=12), and hip pain (38%, n=11). Commonly identified risk factors included diabetes mellitus (17%, n=5), steroid use (7%, n=2), and malignancy (7%, n=2), although 45% (n=13) of patients had no known underlying conditions (Table 3). In our case, the main risk factor was multiple myeloma, which is a hematologic malignancy associated with profound immunosuppression.

Psoas abscesses are typically classified as primary, arising from hematogenous or lymphatic spread, or secondary, resulting from contiguous spread of nearby infections^[32]. In several cases, the distinction is challenging. In our review, concurrent infections such as vertebral osteomyelitis/spondylodiscitis (24%, n=7) and sacroiliitis/septic arthritis (21%, n=6) were identified, whereas 34% (n=10) had no additional infectious focus. Our patient had a prior episode of Salmonella bacteremia following gastroenteritis 3 months earlier, with no evidence of abscess formation at that time. This clinical course suggested hematogenous seeding as the likely mechanism of a primary abscess.

Imaging plays a central role in diagnosis. CT remains the gold standard owing to its high sensitivity and specificity, although MRI and ultrasound may be valuable, especially for early detection or in patients where radiation exposure is a concern^[32]. Microbiological confirmation through blood and abscess cultures is critical for guiding targeted therapy^[33]. In the reviewed cases, abscess cultures were positive in 59% (n=17), blood cultures in 55% (n=16), and both in 21% (n=6) of the patients. In our patient, both blood and abscess cultures grew Salmonella spp., although serotyping was not performed.

Optimal management generally requires a combination of antibiotics and drainage, either percutaneous or surgical. Reported antibiotic regimens include fluoroquinolones, ampicillin, trimethoprim/sulfamethoxazole, and third-generation cephalosporins^{[12, 23]}. In our review, drainage was performed in 79% (n=23) of the cases. Treatment duration varied between 5 weeks and 10 months, with most patients achieving full recovery. In the present case, intravenous ciprofloxacin was initiated based on blood culture results, but resistance was later detected in the abscess culture, necessitating a switch to ceftriaxone. Despite applying appropriate therapy and drainage, the patient’s condition deteriorated, and she ultimately died.

Although most cases in the literature showed favorable outcomes, two fatalities were reported. One involved a previously healthy 56-year-old male with a perinephric abscess and aortic wall involvement, likely complicated by vascular compromise^[6]. The second occurred in a 71-year-old male with gastric cancer; treatment failure was likely influenced by inadequate drainage, a short antibiotic course, and immunosuppression^[24]. In our patient, multiple myeloma-related immunosuppression, the emergence of ciprofloxacin resistance, and progressive clinical decline despite appropriate interventions likely contributed to the fatal outcome. Collectively, these cases emphasize the importance of timely diagnosis, effective drainage, and careful consideration of host factors and antimicrobial resistance in determining prognosis.

This report has certain limitations. First, the Salmonella strain was not serotyped, which restricted comparisons with previously published cases. Second, ciprofloxacin resistance could not be assessed at the molecular level, which limited our understanding of underlying resistance mechanisms in this context.

Salmonella-induced psoas abscess is an uncommon but clinically significant condition, and it has been reported in both immunocompetent and immunocompromised individuals. Although most patients achieve favorable outcomes with timely antibiotics and drainage, prognosis worsens with delayed diagnosis, antimicrobial resistance, or underlying immunosuppression. Clinicians should therefore maintain a high index of suspicion in cases of Salmonella bacteremia presenting with musculoskeletal symptoms to facilitate early recognition and optimal management.