Rhodococcus infection on an immunocompromised patient with axial spondyloarthritis: A case report

Abstract

Introduction: Patients with inflammatory arthropathies on anti-TNF therapy are at risk of opportunistic infections, contributing to their overall morbidity and mortality. This case report describes a patient with advanced axial spondyloarthritis who developed a Rhodococcus skin infection with lymphangitic spread from a rose thorn injury to his finger while gardening. He required almost a year of antimicrobial therapy, throughout which he remained off immunosuppression. The case illustrates the importance of timely identification and management of infections, counselling patients on the risks of rare pathogens associated with their behaviours, complications such as thrombotic events, and treatment decisions for patients in prolonged remission. Case description: We describe a case of an 82 year old male patient with axial spondyloarthritis (AxSpA) (advanced, radiographic), associated with Crohn's disease, moderate aortic regurgitation and apical fibrosis on adalimumab since 2008. Other past medical history is significant for multiple non melanoma skin cancers. His disease had been in remission for some years (ASDAS-CRP 1.8) when he contacted the rheumatology nurse helpline complaining of non-healing wounds on his arm. He was reviewed clinically and found to have an ulcerating rash which appeared to have spread from his left hand to his left forearm. He admitted to noticing this rash after sustaining an abrasion to his left hand from a rose thorn while gardening four months prior. Of note, he also owned a tropical fish tank which he occasionally cleaned. He had stopped taking adalimumab of his own accord when he developed the rash. The dermatology team performed an incisional biopsy of an elbow lesion, which revealed active inflammation with focal microabscesses. There was no growth from standard culture and no acid-fast bacilli seen but Rhodococcus species was detected on bacterial DNA from 16s PCR. He was managed under the infectious diseases team who initially treated with linezolid, levofloxacin and doxycycline, before switching to azithromycin 250 mg OD and rifampicin 600 mg OD. He remained on this for eleven months, under regular review by infectious diseases and rheumatology. He had a minor flare of AxSpA involving the cervical spine but did not require any immunosuppression (ASDAS-CRP 1.9). During this time, he developed a common femoral DVT, managed with enoxaparin. He restarted adalimumab subsequently and remained stable. Discussion(s): Rhodococcus is an aerobic Gram-positive bacteria closely associated with mycobacterium and corynebacterium. It most commonly infects plants (R. fasians) and foals (R. equi), but other hosts include pigs, cattle and immunocompromised humans, mainly through exposure to soil, aquatic environments and agriculture, where is causes abscesses and is spread via the lymphatic system. Some strains can lead to bacteraemia and in severe cases to CNS, mediastinal and intra-abdominal involvement, as well as osteomyelitis and spondylodiscitis. Relapse may occur after treatment either at the same site or a distant site. Immunosuppression should be withheld to allow for complete treatment of the pathogen with prolonged courses of antibiotics. This patient's AxSpA and Crohn's remained stable even after cessation of adalimumab, which allowed for straight forward treatment, but it is important to consider possible complications had the patient's disease not been stable throughout this time, as even short courses of steroids could have impeded or prolonged the treatment of the infection. Interestingly, Rhodococcus has been showed to biotransform corticosteroids into more potent forms, and has pharmacological implications. As his disease had been extremely well controlled previously, it was felt that a biologic switch should only be considered if absolutely necessary based on flares, and he restarted adalimumab after completion of Rhodococcus treatment. This was an interesting case as it highlights the risk of opportunistic and rare infections in patients on immunosuppression, and the importance of history taking and prompt clinical assessment in order to identify organisms to achieve timely treatment and avoid complications. It also forces us to reflect on the benefits of continuing treatment for patients who are in prolonged remission and the importance of continually assessing for risks associated with treatment. Key learning points: Although Rhodococcus skin and soft tissue infection is not a common presentation, gardening is a popular hobby amongst our population and so perhaps we should be advising patients to avoid garden pathogens by wearing gloves and being aware of any open wounds. This patient tended to his fish tank, so would have been at risk of mycobacterium marinum as well. We often counsel patients on avoiding exposure to people with common infections, and recommend on the uptake of non-live vaccines, but this case raises a consideration on the extent to which we should be exploring patient's hobbies and interests, identifying risks and providing counselling on preventative measures to avoid associated exposure to certain rarer pathogens, so that patients can make an informed decision about the risks associated with their behaviours. Further, when counselling patients in clinic, it is important to educate on signs and symptoms of potential infection to avoid delays in treatment. This patient admitted to having had the rash for four months prior to calling the rheumatology helpline. Another learning point relates to this patient's deep vein thrombosis which he developed some months into treatment for Rhodococcus. Patients with AxSpA are at higher risk of VTE and in his case his risk was compounded by active skin infection. The haematology team discussed the length of anticoagulant treatment with the patient and a joint decision was made to stop once infection had been treated, given that his disease was in remission. As a further learning point, rifampicin precluded the use of oral anticoagulants, so he was treated with subcutaneous heparin.