Rheumatology key message Pyomyositis is a potential differential diagnosis of hip septic arthritis in patients on immunosuppressive treatment. Sir, a 77-year-old female patient with a 29-year history of well-controlled seropositive RA was admitted to our hospital with a 1-day history of acute onset severe right hip pain that was worse on weight bearing. She reported no preceding trauma and her RA was treated with LEF and certolizumab pegol. She had a previous history of septic arthritis of the right hip 12 years ago, was a non-smoker and did not have diabetes. She had presented similarly 8 months prior to this admission with right hip pain, painful weight bearing and restricted movement of the right hip. At this time she was apyrexial but had a CRP of 183.5 mg/l (normal <5 mg/l).The white cell count was normal. Blood cultures were negative. An MRI hip at that time revealed a rim enhancing area lateral to the tendon of the right gluteus maximus muscle with oedema in the surrounding muscle fibres (Fig. 1A). There was also a moderate hip joint effusion with capsular enhancement (Fig. 1A). She received initial antibiotic therapy for possible septic arthritis, but in the absence of any marrow involvement or erosions in the underlying bones of the hip joint in the MRI scan (Fig. 1B and C), this was felt at the time to be reactive in nature, likely as part of an RA flare. The antibiotics were discontinued and the patient was managed with anti-inflammatories and analgesics following which her CRP improved. She remained on LEF and certolizumab pegol therapy. Fig. 1 View largeDownload slide MRI scan images in pyomyositis (A) Coronal T2 MR shows a high signal intensity fluid collection lifting the thin low signal synovial capsule (long black arrow) adjacent to the right greater trochanter. Prominent linear high signal noted in the adjacent musculature (short black arrows). (B) Coronal T1 MR demonstrates corresponding low T1 signal in the above fluid collection (arrow). The underlying femoral marrow shows normal signal intensity (asterisks). (C) Sagittal T1 MR after intravenous contrast demonstrates band-like ill-defined intramuscular enhancement (short arrows). SF collections noted with smooth capsular rim enhancement anteromedial and posterolateral (long arrows) to the greater trochanter. Note normal marrow signal with no intra-osseous enhancement. Fig. 1 View largeDownload slide MRI scan images in pyomyositis (A) Coronal T2 MR shows a high signal intensity fluid collection lifting the thin low signal synovial capsule (long black arrow) adjacent to the right greater trochanter. Prominent linear high signal noted in the adjacent musculature (short black arrows). (B) Coronal T1 MR demonstrates corresponding low T1 signal in the above fluid collection (arrow). The underlying femoral marrow shows normal signal intensity (asterisks). (C) Sagittal T1 MR after intravenous contrast demonstrates band-like ill-defined intramuscular enhancement (short arrows). SF collections noted with smooth capsular rim enhancement anteromedial and posterolateral (long arrows) to the greater trochanter. Note normal marrow signal with no intra-osseous enhancement. On this current admission she was found to be pyrexial (38.4°C), complained of severe right hip pain and had a gross limitation of the right hip movement. The temperature overlying the hip was raised but there was no external erythema or discharge. Blood tests revealed a CRP of 275.8 mg/l (normal <5 mg/l) and white cell count of 15.3 × 109/l (predominantly neutrophils). All other joints were stable. An MRI scan of the hip was requested but not carried out as the radiologists felt that the MRI would not be able to distinguish between infection and inflammation. The patient was commenced on meropenem for a presumed diagnosis of septic arthritis and underwent an urgent surgical joint washout. Surprisingly during surgery, no florid synovitis of the hip was seen and there was no bone surface or joint damage, contrary to that expected in a septic joint on a background of chronic inflammatory arthritis. Rather, she was noted to have extensive erythematous fat and turbid fluid under the fascia lata. Frank pus discharged as soon as the adductors were detached and tracking of pus was seen under the gluteus medius. Blood culture performed at admission grew Gram-negative bacilli, Enterobacter cloacae, but the pus cultures were negative (including for TB) possibly due to antibiotics administered prior to surgery. The intra-operative findings were felt to be in keeping with pyomyositis causing a reactive joint effusion rather than a primary septic arthritis of the hip causing pus to track down the muscle planes. The patient was treated with intravenous antibiotics and made a good clinical recovery. Due to the anatomical match of the current intra-operative findings with the MRI scan performed during the previous admission, it was felt that the presentation 8 months previously was most likely low grade pyomyositis that was partially treated but had now relapsed. Pyomyositis is a rare infection of skeletal muscle and immunosuppression is thought to increase the risk . It has a predilection for large muscles and the majority of reported cases involve muscles around the hip . Staphylococcus aureus is by far the most common causative organism reported and Gram-negative organisms, as in this case, are rare and most frequently found in those who are immunocompromised [1, 2]. Enterobacter cloacae is a common environmental organism and also a commensal in the human gastrointestinal tract. It is gaining increasing recognition as a cause of healthcare-associated infections and may cause a wide range of infections including bacteraemia, osteomyelitis, skin and soft tissue infection, and septic arthritis and has high rates of antibiotic resistance . It has been associated with pyomyositis although only a few cases have been described thus far [2, 4]. Pyomyositis has been reported previously in patients receiving a range of biologic agents, including infliximab , anakinra  and tocilizumab , and also conventional DMARDs, including LEF . This is, to our knowledge, the first report of isolated pyomyositis in association with certolizumab pegol therapy. It is probable that concomitant LEF treatment compounded the risk. Though rare, pyomyositis is an important, yet easily overlooked differential diagnosis for septic arthritis, particularly in the hip where clinical signs may be limited. MRI is the imaging modality of choice and treatment is focused on drainage of the pus and appropriate antimicrobial chemotherapy. Funding: No specific funding was received from any bodies in the public, commercial or not-for-profit sectors to carry out the work described in this manuscript. Disclosure statement: The authors have declared no conflicts of interest. References 1 Bickels J , Ben-Sira L , Kessler A , Wientroub S. Primary pyomyositis . J Bone Joint Surg Am 2002 ; 84 : 2277 – 86 . Google Scholar CrossRef Search ADS PubMed 2 Gousseff M , Lanternier F , Ferroni A et al. Enterobacter cloacae pyomyositis complicating chronic granulomatous disease and review of gram-negative bacilli pyomyositis . Eur J Clin Microbiol Infect Dis 2013 ; 32 : 729 – 34 . Google Scholar CrossRef Search ADS PubMed 3 Davin-Regli A , Pagès J-M. Enterobacter aerogenes and Enterobacter cloacae; versatile bacterial pathogens confronting antibiotic treatment . Front Microbiol 2015 ; 6 : 392 . Google Scholar CrossRef Search ADS PubMed 4 Falasca GF , Reginato AJ. The spectrum of myositis and rhabdomyolysis associated with bacterial infection . J Rheumatol 1994 ; 21 : 1932 – 7 . Google Scholar PubMed 5 Kane D , Balint PV , Wood F , Sturrock RD. Early diagnosis of pyomyositis using clinic-based ultrasonography in a patient receiving infliximab therapy for Behçet’s disease . Rheumatology 2003 ; 42 : 1564 – 5 . Google Scholar CrossRef Search ADS PubMed 6 Migkos MP , Somarakis GA , Markatseli TE et al. Tuberculous pyomyositis in a rheumatoid arthritis patient treated with anakinra . Clin Exp Rheumatol 2015 ; 33 : 734 – 6 . Google Scholar PubMed 7 Raine C , Hamdulay SS , Khanna M , Boyer L , Kinderlerer A. An unusual complication of tocilizumab therapy: mRI appearances of thenar eminence pyomyositis . Joint Bone Spine 2013 ; 80 : 222 . Google Scholar CrossRef Search ADS PubMed 8 Grover R , Dhir V , Aneja R et al. Severe infections following leflunomide therapy for Rheumatoid Arthritis . Rheumatology 2006 ; 45 : 918 – 20 . Google Scholar CrossRef Search ADS PubMed © The Author(s) 2018. Published by Oxford University Press on behalf of the British Society for Rheumatology. All rights reserved. For permissions, please email: firstname.lastname@example.org This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices)
Rheumatology – Oxford University Press
Published: Apr 6, 2018
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