E112 Anti-HMGCR immune mediated necrotising myopathy: a case series of twenty-four patients diagnosed in University Hospitals of Liverpool Group

Background/Aims Anti-HMGCR immune mediated necrotising myopathy (IMNM) is a rare form of idiopathic inflammatory myositis (IIM). In adults, it is often associated with previous statin use and is associated with a unique auto-antibody targeting the 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) enzyme. In contrast to the direct myotoxic effects of statins, which are often reversible on withdrawal of the drug, people with anti-HMGCR IMNM experience ongoing symptoms, despite statin cessation. We present a case series of 24 patients diagnosed with anti-HMGCR IMNM in a single teaching hospital. Methods We identified adult patients diagnosed with anti-HMGCR IMNM, who attended the myositis clinic in Liverpool from January 2019-September 2025. Patients were classified as having anti-HMGCR IMNM based upon the presence of proximal muscle weakness, elevated CK, a positive HMGCR antibody and radiological and/or histological evidence of inflammation. Demographic data, date of diagnosis, co-morbidities, statin-related factors (type of statin, dose, duration) and laboratory results (baseline CK, anti-HMGCR titre, auto-antibody profile) were documented. In terms of clinical profile, presence of extra-muscular symptoms, dysphagia and association with cancer were also captured. Results Twenty-four patients met criteria for anti-HMGCR IMNM; 12 (50%) were male and the mean age at diagnosis was 65 years (range 56 - 74 years). Sixteen (66.6%) patients had diabetes mellitus. All the patients (100%) had previous exposure to atorvastatin. Median duration of statin exposure was 3 years prior to presentation. The statin dose was documented in 87.5%, among whom the median dose of atorvastatin was 20mg once daily. Raynaud’s phenomenon was reported in 9.5% of patients. None had skin rash or any evidence of interstitial lung disease. Two (9.5%) patients had dysphagia. There was no evidence of cancer-associated myositis in this study group. Mean CK reported at initial presentation was 6840 IU/L (range 339 - 20,660). Anti-HMGCR titre was available in 87.5% patients, with a mean value of 135.35 IU/L. Interestingly, the majority of patients (75%) were diagnosed in the last 3 years. Conclusion Anti-HMGCR IMNM is a rare condition that should be considered in patients presenting with proximal muscle weakness and a raised CK. Although the condition is recognised in children and statin-naïve patients, in our cohort, the condition was associated with prior statin use. Patients had been on statins for a median of 3 years prior to presentation. Extra muscular symptoms and malignancy were not detected at presentation. Early recognition and diagnosis of Anti-HMGCR IMNM is important to guide appropriate management decisions.