Parvimonas micra causing native hip joint septic arthritis

Abstract

Parvimonas micra is a bacterium normal to oral and gastrointestinal flora that has been implicated in cases of discitis, osteomyelitis, and prosthetic joint infections, often involving dental procedures or periodontal disease. It is an extremely rare cause of infection outside of these circumstances. We describe a case of septic arthritis of the native hip joint due to P. micra.

Parvimonas micra (previously Peptostreptococcus micros) is an anaerobic, fastidious, gram-positive coccus known to be normal oral and gastrointestinal flora.¹ While it has often been reported as the cause of periodontal and gingival infections, infections outside of the oral cavity have rarely been reported and include the spine, knee, and iliopsoas.^2–4 However, due to its atypical presentation and difficulty culturing, this organism may be an underreported cause of infection.⁵ We present a case of septic arthritis of the native hip joint caused by P. micra in a patient with subacute unilateral hip pain.

CASE REPORT

A 65-year-old man with known coronary artery disease, chronic obstructive pulmonary disease, and non-Hodgkin’s lymphoma (in remission for 16 years, not on any immunosuppressants at the time of presentation) presented to the emergency department with subacute left hip pain. Approximately 4 months earlier, he fell off his bed and developed acute hip pain. Upon initial presentation to the emergency department, x-ray (Figure 1a) and computed tomography images revealed no fractures, and he was treated with physical therapy. He underwent two corticosteroid injections of the left hip bursa approximately 2 months prior to presentation, with only 7 days of relief after each injection. He then developed nausea and flushing in association with worsened hip pain, prompting him to present to our facility.

Figure 1.

Patient imaging. (a) X-ray at the time of presentation and (b) sagittal computed tomography on hospital day 1 reveal significant superior joint space narrowing to the left hip joint with joint space loss, femoral head flattening, and periarticular sclerosis. (c) Axial and (d) coronal magnetic resonance imaging on hospital day 1 demonstrate marrow edema, complex joint effusion, and intramuscular complex fluid collections.

The patient denied any other subjective symptoms of systemic illness. He denied back or knee pain but reported occasional pain radiating from the hip to the knee. Notably, he denied any recent illness, pneumonia, abscesses, prior tooth or dental procedures, infections, other painful joints, or open wounds. He had no prior history of surgery to the affected extremity. Physical exam disclosed a well-appearing gentleman in no acute distress. Cardiac, pulmonary, and abdominal examinations were unremarkable. The skin over the hip and buttock areas was intact. Passive and active range of motion were decreased and painful. Initial laboratory values included an elevated white blood cell count of 11,400 (75% neutrophils) and elevated inflammatory markers, including an erythrocyte sedimentation rate value of 89 mm/h and a C-reactive protein value of 28.29 mg/dL. Imaging showed severe loss of joint space with complex fluid collections concerning for septic arthritis and pyomyositis abscesses (Figure 1b–1d).

Diagnostic arthrocentesis was performed followed by urgent arthrotomy, irrigation, and debridement of the hip joint with abscess drainage the following morning. Culture results obtained on a blood agar plate of the synovial fluid from the arthrocentesis and the surgical specimens both grew P. micra. This organism grew on two separate days from two separate locations and was thus confirmed. Cultures from the abscesses demonstrated no growth. The patient was empirically started on vancomycin and piperacillin tazobactam. C-reactive protein levels were trended during the hospital stay (Figure 2). The patient was then switched to ampicillin/sulbactam and doxycycline following susceptibility results and remained on this treatment regimen for 6 weeks through discharge to a long-term rehabilitation facility.

Figure 2.

C-reactive protein trend during the patient’s hospital stay. Each data point corresponds to daily values from admission. The reference range is between the dotted lines.

DISCUSSION

P. micra has been described in a few case reports as the source of infection, but it is extremely rare for it to cause an infection of a native hip joint, especially in a patient without a history of recent dental procedures or infections. Initial reports described a patient with septic arthritis of the knee. Interestingly, while our patient was in remission from hematologic malignancy, the patient described by Riesbeck et al was diagnosed with multiple myeloma during his admission for septic arthritis, although the extent of this association remains unclear.⁶ Moreover, the patient described in the report by Sultan et al⁷ also received steroid injections just prior to presentation of the septic joint, though intra-articular.

Our case demonstrates that septic arthritis due to P. micra should be considered in a patient with subacute hip pain. While native joint infections are extremely rare, such cases might be underreported due to historical difficulty in culturing this organism.⁵ For best results in collecting and identifying anaerobic organisms, the specimen should be obtained from the leading wound edge or from a deep fluid collection after proper local debridement. The specimen should be sent in an anaerobic environment and is commonly cultured on the anaerobic medium thioglycolate broth.⁸ Two of the previously reported risk factors were present in our patient, notably a history of hematologic malignancy and corticosteroid injection. Other risk factors based on current literature include crystal-induced arthritis, dental infection, concurrent pseudogout, and previous dental infections.^5,7,9,10 Further studies, though, are needed to explore the nature of the relationship of such factors and septic arthritis due to this pathogen. Finally, the iliacus and psoas abscesses should not be overlooked, as pyomyositis can present with insidious onset, and uncontrolled pyomyositis can progress with significant morbidity, including septic arthritis.¹¹ A high clinical suspicion for an infectious process with atypical pathogens is necessary when hip pain without evidence of trauma or radiographic abnormalities fails to resolve with conservative measures.