Emphysematous osteomyelitis in hematological malignancies: tales of two cases

Abstract

Emphysematous osteomyelitis (EOM) is defined as the presence of gas forming bacteria within bones. It is seen in patients with morbid conditions like immunosuppression, diabetes, patients on chemotherapy, in cancer patients and in intravenous drug abusers. We present two cases of emphysematous osteomyelitis in patients with hematological malignancies; lymphoma and leukemia. Both the patients had similar clinical presentations with fever, localized swelling, and pain. Both patients underwent sonography (USG) and contrast-enhanced computed tomography (CECT) and imaging diagnosis of EOM was made. Microbiological confirmation of the causative organism was done and patients were started on appropriate antibiotics. Both patients responded very well to the treatment. Imaging findings and treatment outcomes are discussed, highlighting the challenges in managing this rare complication.

Introduction

Emphysema osteomyelitis (EOM) is a condition, characterized by intraosseous gas locules. It is rarely encountered in clinical practice. The first case of EOM was reported by PC Ram in the year of 1981 where he described 3 cases of EOM affecting tibia, fibula, and the pelvic bones in patients who had undergone some surgical procedures in the recent past [1]. The EOM is associated with increased morbidity and mortality, reported as high as ~ 32% [2], so early suspicion and accurate diagnosis is must in each and every case. EOM requires aggressive medical and surgical management. EOM commonly seen in a patient with compromised immune system predominantly in the diabetic group [3] and patients with the malignancy. The most common bones affected in EOM are the vertebrae followed by the pelvic bone and the femur [3]. The most common culprit organisms are the anaerobic bacteria from the Enterobacteriaceae family and the most common route of infection is hematogenous [3].

Hematological malignancies often require intensive chemotherapy and EOM can be seen due to compromised immune systems. In the literature, most of the cases of EOM have been described in diabetic patients or as a postoperative complication. We could not find any case of EOM in patients with hematological malignancy, so here we would describe two cases of EOM in patients with hematological malignancy affecting pelvic bones and the femur.

Case 1 presentation

A 46 year old non-diabetic female patient was diagnosed with stage 4 diffuse large B-cell lymphoma (DLBCL). She was started on R-CHOP chemotherapy regimen. During the course of treatment, she presented with bilateral lower limb pain and weakness that had persisted for 15 days. The weakness was predominantly in the proximal muscle group rather than distal muscles. Additionally, she also experienced high-grade fever. The clinical examination revealed swelling and erythema in the bilateral gluteal regions.

After clinical examination, she was referred for sonographic (USG) evaluation of bilateral gluteal swelling. The USG revealed ill-defined, thick-walled collections in the gluteal muscles bilaterally. There was no significant vascularity in these collections. Post USG, contrast-enhanced CT (CECT) scan of abdomen and pelvis was performed which revealed multiple variables sized irregular low attenuating lesions (collections) with peripheral enhancement and air foci within them in the bilateral iliopsoas and gluteal muscles (Fig. 1). Bilateral pelvic bones showed permeative erosions with numerous irregular small-sized air foci in the medullary cavities, giving “pumice stone” appearance (Fig. 1b, c). These findings were consistent with a diagnosis of emphysematous osteomyelitis. Multiple discrete and conglomerated enhancing enlarged lymph nodes were also seen in the retroperitoneum sandwiching the vessels, consisting with a diagnosis of lymphoma (Fig. 1d).

Fig. 1.

46 year old female patient with stage 4 DLBCL on R-CHOP chemotherapy, CECT abdomen, & pelvis shows bilateral peripherally enhancing irregular-sized iliopsoas collections (a), permeative erosions involving bilateral pelvic bones with air foci in the medullary cavities (b and (c), consistent with emphysematous osteomyelitis. Multiple discrete and conglomerated enlarged lymph nodes in the retroperitoneum sandwiching the vessels suggestive of lymphoma (d)

Post-imaging workup, pus aspirated from the collections for a tissue diagnosis. The pus culture detected Klebsiella pneumoniae. On antimicrobial susceptibility test (AST), this organism showed sensitivity for amikacin and meropenem. The blood culture was sterile.

After confirmed microbiological diagnosis of EOM, the patient was initiated on broad-spectrum antibiotics. The patient had significant clinical improvement with a reduction in fever spikes and the size of the collections. Follow-up CT imaging, post 2 weeks of antibiotic course, showed a marked reduction in the size of the iliopsoas and gluteal collections, although there was an increase in bone erosion. Due to the progressive bone erosion observed, the patient was started on zoledronic acid to address potential bone-related complications. On further follow CT scan, there was significant bony healing seen.

Case 2 presentation

A 44 year old diabetic female patient, known for acute lymphoblastic leukemia (ALL), was on consolidation chemotherapy (vincristine, daunorubicin, pegaspargase, and prednisolone). While she was on chemotherapy, she presented with complaints of swelling and pain in right hip. She was unable to bear her weight also. A sonography was performed as a first imaging modality which revealed a well-defined thick-walled anechoic collection in the gluteal and thigh muscles on the right side. Subsequently, a CECT of abdomen and pelvis was done which revealed a large hypodense collection with peripheral enhancement in the anterior and posterior compartment of the thigh (Fig. 2a). The right femoral cortex was thickened, remodeled with small cloaca, and sequestrum (Fig. 2b). Multiple irregular variable sized small air foci were also seen in the medullary cavity (Fig. 2c, d), giving “pumice stone” appearance, consistent with a diagnosis of EOM.

Fig. 2.

A 44 year old diabetic female patient on consolidation chemotherapy for ALL, CECT for pelvis shows, well-defined peripherally enhancing thick-walled collection in the anterior and posterior compartment of the thigh (a, c). The right femoral cortex was thickened, remodeled with small cloaca (b), sequestrum (c) with air foci in the medullary cavity (d), consistent with emphysematous osteomyelitis

To microbiologically confirm the diagnosis, USG-guided pus was aspirated from the collections which detected Gram-negative rods (E. coli). The blood culture was sterile. On AST, the organism was sensitive to Tigecycline, Amikacin, and Colistin. She was started on broad-spectrum antibiotics based on culture sensitivity. After 12–13 days of antibiotics course, she became afebrile with the resolution of right hip pain. Her antibiotic course was discontinued and she was continued on consolidation chemotherapy with appropriate supportive therapy.

Discussion

EOM is a type of subacute osteomyelitis which is caused by gas forming bacteria and it will appear as intraosseous gas. This condition is associated with high mortality [2], commonly seen in patients with suppressed immune systems like patients with diabetes and patients with malignancy. Other important risk factors are intravenous drug abuse [4], sickle cell anemia [5], pyelonephritis [6, 7], and long-term steroid use. However, cases of spontaneous EOM [8], in patients with septic arthritis [9] and as a postoperative complication [10, 11] have been described in the literature. The most common location of EOM is the vertebrae followed by pelvic bones and the femur [3]. However, cases of EOM involving the clavicle [12], calcaneum [13], upper limb bones, and multifocal EOM [5, 14] are well documented in the literature.

Most commonly causative organism is Escherichia coli (E. coli) which is an anaerobic bacterium belonging to the Enterobacteriaceae family. Other culprit organisms are Klebsiella pneumoniae, Enterobacter aerogenes, Clostridium species, and anaerobes, such as Anaerococcus, Peptostreptococcus, and Fusobacterium [4]. Both monomicrobial and polymicrobial infections have been reported. Infection with rare facultative anaerobes; M. Morganii also has been described as a cause of pubic bone EOM [15]. The most common route of spread is hematogenous; however, it can be caused by direct inoculation of the organism from the external side as seen in open wound or post-surgical cases [1], or due to spread from the adjacent infections as seen in cases of septic arthritis [9] and in patient with infected abdominal aortic aneurysm [10].

Imaging plays an important role to diagnose EOM. USG can be done in patients who are presented with localized swelling and it also helps in doing USG-guided aspiration from the collection for microbiological confirmation. The plain radiograph can identify areas of air foci within the soft tissue, but it is not sensitive to intraosseous gas.

CT is the investigation of the choice for EOM. On CT, EOM is diagnosed as the presence of air foci within the medullary cavity. Apart from intraosseous gas, CT can assess soft-tissue air, any collection in the adjacent soft tissue, any cortical breach, or bony remodeling.

However, EOM is not the only differential for intraosseous air. Intraosseous air can be seen in a variety of conditions like degenerative disease of the spine, post-trauma, open fracture/penetrating wounds, post-surgery, and in malignant conditions like osteonecrosis [2]. The “pumice stone sign” has been described as a distinct imaging sign for EOM [16]. On CT, it is described as clusters of greater than 3 distinct foci of intramedullary gas with irregularly irregular sizes ranging between 2 and 5 mm with resemblance to surface appearance of pumice stone. This sign was seen in 96% of cases of emphysematous osteomyelitis [16].

Management of EOM includes broad-spectrum antibiotics with drainage of collection/abscess if needed. The drainage can be done using USG guidance if superficial collection or using CT guidance if it is in deep location. Surgical debridement and amputation may be required in some cases if needed.

We described two cases of EOM in patients with hematological malignancy; one of them was diabetic too. Both of the patients presented with localized swelling and pain and imaging confirmed the diagnosis of EOM in both. Both the patients responded well to broad-spectrum antibiotics and were continued on chemotherapy for underlying malignancy.

Conclusion

EOM can be seen in any patient with suppressed immune system, mainly in diabetes and in malignancy. It is associated with high mortality. It can be diagnosed confidently on imaging (CT) which also helps in management and response assessment. The “pumice stone sign” has been described for EOM, to differentiate it from other causes of intraosseous gas.

Author contributions

M. S. wrote the manuscript. All other authors reviewed and revised the manuscript and approved it for submission.

Funding

None.

Data availability

All data and materials are available from the corresponding author, upon reasonable request.

Declarations

Conflict of interest

All authors declare that they have no competing interests.

Ethical approval

Ethical approval was not obtained for this as this is a case report.