Abstract
Background:
Anti–3-hydroxy-3-methylglutaryl-CoA-reductase (HMGCR) antibodies are associated with immune-mediated necrotising myopathy (IMNM), a rare disease typically requiring multi-modal immunosuppression.1,2 PathWest Laboratory Medicine (PathWest) has been the sole provider in Western Australia (WA) of an anti-HMGCR ELISA assay since 2015. Positive predictive value (PPV) of this assay for a WA cohort (2015–2019) was calculated as 88%.3 This was the benchmark for performance set for audit of a WA cohort encompassing 2020–2023.
Methods:
Identified anti-HMGCR requests to PathWest between January 2020–December 2023, and identified positive results (reference: < 11 relative units). Exclusion criteria: aged under 18 years; non-WA resident; requested outside a tertiary public hospital. Electronic records reviewed to confirm HMGCR-IMNM diagnosis by an immunologist, rheumatologist or neurologist. Calculated PPV.
Results:
The number of anti-HMGCR requests from WA between 2020–2023 was 1,120. Twenty-five (2%) were positive. Of these, three were considered false positives resulting in a PPV of 88%. The PPV was previously calculated as 88% from a WA cohort of patients between 2015–2019 with application of the same exclusion criteria. This audit demonstrates the assay remains robust in its performance and meets the benchmark PPV of 88% provided by analysis of our index cohort.
References:
1. Allenbach Y, Benveniste O, Stenzel W, et al. Immune-mediated necrotizing myopathy: clinical features and pathogenesis. Nat Rev Rheumatol 2020; 16: 689–701.
2. Mammen AL, Chung T, Christopher-Stine L, et al. Autoantibodies against 3-hydroxy-3-methylglutaryl-coenzyme A reductase in patients with statin-associated autoimmune myopathy. Arthritis Rheum 2011; 63: 713–21.
3. Tan E, Knight J, Khonasti S, et al. Clinical associations of patients with anti-3-hydroxy-3-methylglutaryl CoA reductase antibody-associated immune-mediated necrotising myopathy. Intern Med J 2023; 53: 1846–53.