Pyomyositis presenting as myonecrosis secondary to methicillin-resistant Staphylococcus aureus bacteremia in chronic lymphocytic leukemia

AABSTRACT

The incidence of pyomyositis in immunocompromised patients with HIV, diabetes, myelodysplastic syndromes, and acute lymphocytic leukemia is well documented. However, there are only a few reports of pyomyositis and myonecrosis in patients with chronic lymphocytic leukemia (CLL). We present a rare case of pyomyositis presenting as myonecrosis secondary to methicillin-resistant Staphylococcus aureus bacteremia in a 72-year-old patient with CLL. Pyomyositis, although rare, warrants increased provider awareness and management, especially among CLL patients who pose diagnostic and treatment challenges.

Pyomyositis is a skeletal muscle infection commonly associated with abscess formation and causes include mechanical trauma and hematogenous spread of infection.¹ In the United States, the incidence of pyomyositis increased threefold between 2002 and 2014.¹ Human immunodeficiency virus, diabetes mellitus, myelodysplastic syndromes, and acute lymphocytic leukemia are risk factors for the development of infection.^1,2 However, reports of pyomyositis associated with chronic lymphocytic leukemia (CLL) are limited.^3,4 To the best of our knowledge, our case is one of the first to demonstrate non–abscess-associated pyomyositis presenting as myonecrosis in a patient with CLL.

CASE REPORT

A 72-year-old man with refractory CLL on obinutuzumab presented with altered mentation, dyspnea, and right shoulder pain. Signs and symptoms were positive for tachycardia and right upper extremity (RUE) tenderness. Pertinent negatives included normal body temperature, stable blood pressures, and a normal range of motion of the upper extremities. Initial laboratory tests were significant for hemoglobin 9.2 g/dL (reference range 13.2–16.6 g/dL), platelet count 87 × 10⁹ cells/L (reference range 135–317), white blood cell count 0.6 × 10⁹ cells/L (reference range 3.4–9.6), and absolute neutrophil count 0.16 × 10⁹ cells/L (reference range 1.56–6.45). Computed tomography angiogram of the chest showed bibasilar nodular and ground glass opacities suggestive of community-acquired pneumonia with risk factors for multidrug-resistant organisms. Broad-spectrum intravenous antibiotics were initially started but then narrowed to vancomycin upon positive methicillin-resistant Staphylococcus aureus (MRSA) blood cultures.

Throughout the hospitalization, disseminated bacteremia with multiorgan involvement was suspected and treated accordingly. The patient’s RUE pain worsened as he developed progressive edema and weakness. There were no sensory deficits. Magnetic resonance imaging (MRI) of the right shoulder demonstrated loss of normal muscle fiber architecture and generalized edema of multiple muscles as well as large areas of nonenhancement consistent with myonecrosis (Figure 1). The patient also had an elevated aldolase at 11.5 U/L (reference range <7.7 U/L) and creatine kinase at 475 U/L (reference range 39–308 U/L). Computed tomography–guided core needle biopsy of the right posterior deltoid muscle revealed focal necrotizing inflammation in the muscle. Culture of the biopsy sample was positive for MRSA, which confirmed the diagnosis of MRSA pyomyositis (Figure 2).

Figure 1.

Axial T1-weighted post-contrast magnetic resonance image of the right shoulder at the level of the humeral head (HH) and glenoid process of the scapula (GP) demonstrates lack of enhancement (dark gray signal delineated by arrows) of the posterior deltoid muscle and the superficial portions of the infraspinatus muscle, consistent with nonviable muscle tissue.

Figure 2.

Computed tomography–guided right posterior deltoid muscle fine needle muscle biopsy. Focal necrotizing inflammation containing aggregates of bacterial cocci (arrows). Culture of the sample yielded methicillin-resistant Staphylococcus aureus.

Thereafter, we suspected the source of the RUE pain, pneumonia, and bacteremia was from a right anterior chest port for chemotherapy. The port was removed by the interventional radiology service. After 72 hours of negative subsequent blood cultures, a peripherally inserted central catheter line was placed for outpatient treatment with 6 weeks of intravenous vancomycin plus 1 week of ceftaroline. The patient was discharged on this antibiotic regimen. At the end of the patient's hospitalization, his RUE weakness and dyspnea significantly improved. However, he expired 8 months after his initial admission due to multiple readmissions for neutropenic fever and sepsis.

DISCUSSION

Pyomyositis is a microbial infection of the striated muscle and can be a complication of hematologic malignancy.^1,2,5–8 Pyomyositis has an estimated mortality rate between 0.89% and 23%⁹; therefore, a timely diagnostic workup and treatment are important for preventing death. For suspected pyomyositis, current Infectious Diseases Society of America practice guidelines recommend 1) MRI to establish the diagnosis, 2) blood or abscess cultures with collection drainage, 3) empiric intravenous vancomycin plus enteric gram-negative bacilli coverage for the immunocompromised, and 4) 2 to 3 weeks of intravenous antibiotics.¹⁰ The MRI in our patient demonstrated edema and enhancement within the muscle tissue consistent with active inflammation in viable muscle tissue as well as large areas of intramuscular nonenhancement consistent with areas of nonviable muscle tissue or myonecrosis. Previous reports of CLL and non-CLL–associated cases describe MRI findings of intramuscular fluid collections with peripheral contrast enhancement and a “feather-like infiltration,” respectively.^11,12

In prior case reports, CLL patients with pyomyositis presented with weight loss and abscess formation in late-stage disease.^9,12,13 Our patient did not have abscess formation likely due to chemotherapy-induced myelosuppression.¹⁴ The presence of infectious myonecrosis or necrotizing myositis in our patient implies a more aggressive and severe infection. Emergent surgery should be considered but can be deferred if mortality risk is high.^14–19 Our patient was not deemed to be a surgical candidate due to his CLL, inpatient neutropenic fever, and sepsis. Fortunately, he had a favorable clinical response to antibiotics through improved muscular function. Our patient also had an elevated serum creatine kinase and aldolase, which indicates more aggressive muscle damage and was vital in identifying pyomyositis.^20,21 For treatment, we prescribed a longer 6-week duration of vancomycin due to multiorgan involvement and CLL immunocompromise. CLL is categorized by neoplastic B cells that inhibit normal immune cells, change cytokine function, and cause hypogammaglobulinemia.²² The immune dysregulation associated with CLL along with concomitant chemotherapy treatments has been shown to increase rates of infection fourfold through impaired ability to mount an immune response.^3,14,22,23 Lastly, port catheter removal was essential in removing the suspected nidus of infection.²⁴

Overall, pyomyositis presenting as myonecrosis is an important but rare differential consideration in CLL patients who present with bacteremia and localized muscle pain. Laboratory analysis for elevated muscle enzymes and a MRI of the affected area are essential in the evaluation of these patients.