Background/Purpose: Foot involvement is frequently pointed by patients with chronic inflammatory rheumatic diseases (IRD), such as rheumatoid arthritis (RA), spondyloarthritis (SpA) or psoriatic arthritis (PsA). According to previous studies, IRD patients are at higher risk of developing osteomyelitis (rate ratio 10.63), although incidence rate seems to be low (0,17/100 patients-years)¹. Given the increased infectious risk, especially induced by steroids or immunosuppressive drugs, our aim was to report the occurrence of foot osteomyelitis in the patients suffering from IRD and recruited in our center over the last twenty years.

Methods: We performed a monocentric retrospective observational study that collected MISP (Medicalized Information System Program) data in the Montpellier University Hospital, from August 1996 to May 2016. We included all patients with IRD who presentedaclinical suspicion of osteomyelitis (classic inflammation signs, or fever), with confirmation by definite imaging (Magnetic Resonance Imaging, tomography, or radiographic) findings and at least one positive microbiological culture. We excluded patients with isolated soft tissue infection, no microbiological sampling, or no imaging finding, as well as patients with incomplete data about their IRD history (long-term treatments, immunology, erosive status). Two groups were dissociated: the first with foot osteomyelitis patients (FO), the other with osteomyelitis patients not affecting the foot (NFO). In the patient medical file, we collected demographic, clinical, biological and imaging data. The comparison between each group was performed using the Student test for quantitative variables and using a Chi-2 test for qualitative variables.

Results: Among the 235 MISP search findings, we identified 69 bone infections that met the inclusion criteria, of which 41 (59.4%) involving the foot. In the FO group, RA was highly predominant (92.6%), with an advanced (24.6 +/- 13.1 years of evolution) and severe illness (37 cases, 92.5% patients with erosions). Patients were mainly treated by corticosteroids (65.9%), methotrexate (32.1 %) and biologics (28.6%). Diabetes was the most frequent comorbidity (8 cases, 19.5%). Osteomyelitis mainly involved forefoot (75.6%), especially in the first ray (41.1% of infections). Staphylococcus aureus was the most involved organism (53.7%). We significantly found fewer systemic complications (sepsis or endocarditis) in the FO group compared to the NFO group (2.4% vs. 28.6%, p = 0.002). Furthermore, corticosteroids use was associated to a significant risk in the FO group compared to the NFO group (65.9% vs. 39.3%, p = 0,03). No increasing infectious risk was found for biological drugs users in the FO group (31.7% vs 28.6%., p = 0.78).

Conclusion: Description of FO is scarce in IRD. Our study reported a significant occurrence, especially in patients with severe RA using steroids. A special attention should be done to identify risk factors and possibly correct them.

References

1. Doran et al. Frequency of infection in patients with rheumatoid arthritis compared with controls: a population-based study. Arthritis Rheum. 2002 Sep;46(9):2287–93

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/foot-osteomyelitis-in-inflammatory-rheumatic-diseases-a-retrospective-observational-study/