BI35 A 12-month history of a progressive rash on a background of significant long-term immunosuppression

This abstract discusses an unusual rash caused by an atypical infection in a susceptible individual. A 52-year-old patient was referred in 2022 with a 12-month history of a progressive rash on the right leg with tender, inflamed and erythematous lesions. The patient had a background of severe relapsing polychondritis that was diagnosed in 2016. The disease was being managed with prednisolone 30 mg once daily, after previous failure of other immunosuppressive agents including methotrexate, azathioprine and 6 cycles of IV cyclophosphamide. Additionally, the patient was also on co-trimoxazole for Pneumocystis jirovecii pneumonia prophylaxis. On examination, erythematous and violaceous plaques and nodules were noted at the right leg with the lesions clustering and coalescing at the right medial thigh. A few of the lesions appeared infiltrated with pale material. Several warts were noted on the dorsal aspect of the hands, indicating significant immunosuppression. Differential diagnoses considered included the following: a vasculitic process, deposition disorders or an infective process. An urgent biopsy revealed palisaded granulomatous and neutrophilic dermatosis, indicative of an infectious aetiology. The patient was referred to the infectious diseases team. Acid alcohol-fast bacteria culture and whole-genome sequencing revealed a diagnosis of Mycobacteroides chelonae, a nontuberculous mycobacterium. The patient was commenced on 6 months’ treatment with combined doxycycline 100 mg twice daily and clarithromycin 500 mg twice daily. The patient responded well to treatment, with resolution of nodules on treatment completion. This case highlights the need for an increased index of suspicion in patients with a history of significant immunosuppression. Our patient had undergone QuantiFERON Gold (negative) in 2020 prior to IV cyclophosphamide. There is some evidence to suggest that QuantiFERON Gold may have the capacity to identify patients with nontuberculous mycobacteria (Kobashi Y, Mouri K, Yagi S et al. Clinical evaluation of the QuantiFERON-TB Gold test in patients with non-tuberculous mycobacterial disease. Int J Tuberc Lung Dis 2009; 13: 1422–6). There is robust guidance on TB infection screening prior to initiating immunosuppression (interferon-γ release assay and chest radiograph) [National Institute for Health and Care Excellence. Scenario: monitoring of DMARDs. Available at https://cks.nice.org.uk/topics/dmards/management/monitoring-of-dmards/ (last access