Rheumatology key message Rare infections should be suspected in immunocompromised patients with inflammatory arthritis. Sir, in this report, we describe the first ever reported case of discitis caused by streptobacillus moniliformis [rat bite fever (RBF)] confirmed by extended culture. RBF remains a diagnostic challenge owing to the non-specific nature of its presentation. Fever, rash, joint pain and general malaise are considered the cardinal symptoms. Though a rare condition, the mortality rate is between 7 and 10% if left untreated . It is therefore imperative that RBF remains part of the differential diagnosis for a patient with the above symptoms, specifically if a clear history of rat exposure can be elucidated. In immunocompromised patients the diagnosis can be more challenging, with potential increased morbidity and mortality. A 62-year-old Caucasian female patient presented with acute onset of widespread hot, swollen joints and severe lower back pain. She was known to have seropositive RA (positive anti-CCP), which had been well controlled with MTX and subcutaneous tocilizumab. Previously, she had undergone a posterior L4/L5 lumbar fusion and had a left total knee replacement. She reported a 4-day episode of diarrhoea and vomiting preceding the polyarthritis and back pain. Of importance in the social history was that the patient kept horses, with the stables recently being infested by rats. The patient had recently cleaned the stables, subsequently gaining exposure to live rats and their droppings. She did not recall being bitten by rats. Laboratory results revealed clear signs of marked inflammation, including a raised CRP of 218 mg/l. Renal function tests initially showed a creatinine of 210 μmol/l, supporting the diagnosis of stage 1 acute kidney injury. Liver function tests and a urine dipstick were within the normal range. An urgent MRI scan of the back showed oedema in the anterior part of the L5/S1 disc suggestive of early discitis. Despite extensive changes of previous spinal surgery from T11 to L5, which impacts on the quality of the scan and its interpretation, the disc oedema has improved after a few weeks of treatment with antibiotics (Fig. 1). Fig. 1 View largeDownload slide MRI showed oedema of L5/S1 disc (1), which has improved after 6 weeks of treatment with antibiotics (2) Fig. 1 View largeDownload slide MRI showed oedema of L5/S1 disc (1), which has improved after 6 weeks of treatment with antibiotics (2) Subsequently, a L5/S1 disc needle aspiration was performed, alongside an aspiration and washout of knees, ankles and right wrist in theatre and under sterile conditions. SF was straw-coloured from the right knee and thick purulent from the left ankle. This confirmed a polyfocal septic arthritis with an unidentified Gram-negative organism as the offending pathogen. On further examination, S. moniliformis was isolated from the spinal disc and peripheral joint samples via 16 S ribosomal RNA PCR; this remains the diagnostic investigation most frequently reported in the literature . The patient was commenced initially on benzyl penicillin and clindamycin. This was later changed to a 12-week course of oral antibiotics (amoxicillin and clindamycin), which the patient successfully completed following discharge. All immunosuppressive medications were discontinued, although she restarted MTX around 4 weeks after discharge from hospital. RBF is a rare yet lethal bacterial infection, most commonly caused by the Gram-negative bacillus S. moniliformis. The non-acid-fast rod colonizes the upper respiratory tract of healthy rats ; transmission can occur through a direct rat bite, although is more frequently through exposure to rat saliva or urine and faeces. Following S. moniliformis exposure, the incubation period is usually <7 days, however can be as long as 3 weeks. Initial symptoms are a fever, nausea, vomiting, diarrhoea, myalgia and headache. As RBF progresses, a migratory polyarthralgia and tender maculopapular rash with haemorrhagic vesicles can occur [4, 5]. Numerous complications of RBF have previously been reported: infective endocarditis and septic arthritis have both been well delineated in the literature . Other notable complications include meningitis, myocarditis, pericarditis, hepatitis, nephritis and suppurative polyarthritis [5, 6]. This is the first reported case of confirmed discitis on vertebral washout and culture; however, spondylodiscitis shown on MRI only was reported recently in a case of RBF . The mainstay of treatment for suspected cases of RBF is penicillin, often in association with a lincosamide (i.e. clindamycin). In the case described, a 12-week course of oral antibiotics was issued; however, it is worth noting that shorter treatment regimens have demonstrated success . Prompt joint washout and irrigation of purulent material is recommended for associated septic arthritis. The importance of immediate treatment cannot be underestimated, which was particularly relevant for this patient, with long-standing RA on immunosuppressant treatment. In conclusion, septic polyarthritis and spondylodiscitis remain an important differential diagnosis in immunosuppressed patients, as opposed to a flare of their underlying inflammatory disease. It is crucial to take a detailed social history to explore potential precipitating factors and causative organisms. 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 Centers for Disease Control and Prevention . Fatal rat-bite fever—Florida and Washington . Morb Mortal Wkly Rep 2005 ; 53 : 1198 – 202 . 2 Boot R , Oosterhuis A , Thuis HC. PCR for the detection of Streptobacillus moniliformis . Lab Anim 2002 ; 36 : 200 – 8 . Google Scholar CrossRef Search ADS PubMed 3 Paegle RD , Tewari RP , Bernhard WN , Peters E. Microbial flora of the larynx, trachea and large intestine of the rat after long-term inhalation of 100 per cent oxygen . Anesthesiology 1976 ; 44 : 287 – 90 . Google Scholar CrossRef Search ADS PubMed 4 Madhubashini M , George S , Chandrasekaran S. Streptobacillus moniliformis endocarditis: case report and review of literature . Indian Heart J 2013 ; 65 : 442 – 6 . Google Scholar CrossRef Search ADS PubMed 5 Hagelskjaer L , Sorensen I , Randers E. Streptobacillus moniliformis infection: two cases and a literature review . Scand J Infect Dis 1998 ; 30 : 309 – 11 . Google Scholar CrossRef Search ADS PubMed 6 Thong BY , Barkham TM. Suppurative polyarthritis following a rat bite . Ann Rheum Dis 2003 ; 62 : 805 – 6 . Google Scholar CrossRef Search ADS PubMed 7 Nei T , Sato A , Sonobe K et al. Streptobacillus moniliformis bacteremia in a rheumatoid arthritis patient without a rat bite: a case report . BMC Res Notes 2015 ; 8 : 694 . Google Scholar CrossRef Search ADS PubMed 8 Holroyd KJ , Reiner AP , Dick JD. Streptobacillus moniliformis polyarthritis mimicking rheumatoid arthritis: an urban case of rat bite fever . Am J Med 1988 ; 85 : 711 – 4 . 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: Mar 7, 2018
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