Incidence and prevalence of immune‐mediated necrotizing myopathy in adults in Olmsted County, Minnesota

Abstract

Introduction/Aims: Immune-mediated necrotizing myopathy (IMNM) is considered a rare subtype of the immune-mediated myopathies, but its incidence and prevalence are unknown. In this study we aimed to determine the incidence and prevalence of IMNM among adults in Olmsted County, Minnesota. Methods:We identified adult patients with IMNM, as defined by the 2016 European Neuromuscular Centre diagnostic criteria, among residents of Olmsted County, Minnesota over a 20-year period.Results: Seven patients fulfilled the inclusion criteria. Six patients were tested for IMNM antibodies: four were anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) positive, one was anti-signal recognition particle positive, and one was seronegative. The incidence of IMNM during 2010-2019 was 8.3 per million personyears. The prevalence of IMNM in 2010 was 1.85 per 100 000 people at least 50 years of age. Median age at symptom onset was 64 (range, 52-86) years and median time from symptom onset to diagnosis was 3 (range, <1 to 156) months. Statin use among anti-HMGCR IMNM patients, but not the entire IMNM cohort, was higher than in controls (P = .024). Two IMNM patients developed cancers. The incidence of malignancy in IMNM was not higher than that of the general population. Treatment outcome was favorable in all patients except for one patient with delayed treatment and another with insufficient therapy. Among three deceased patients, one died of cancer and another died of IMNM-related cardiorespiratory complications.Discussion: IMNM is a rare disease. Its prevalence is one tenth that of inclusion-body myositis in Olmsted County, Minnesota. IMNM patients in our cohort were not at higher risk for developing cancer.

COVID-19 associated myopathy

“…If we assume that an infection with SARS-CoV-2 doesn’t decrease or increase the probability of developing a disease or health problem X, than we can expect the incidence (occurrence of new cases per year) of that disease or health problem X to be the same in the population of SARS-CoV-2 infected people than in the population from which the incidence was previously derived from (usually this data stem from pre-COVID times). This means that among the roughly 265 million infected people per year – for the sake of this thought experiment we neglect the fact that people can be reinfected - statistically speaking 2552 people would develop dermatomyositis (DM) in the same year that they were infected with SARS-CoV-2 (assuming an incidence of DM of 9.63/Million [40]), 2200 would develop an immune-mediated necrotizing myopathy (IMMN, assuming an incidence of immune-mediated necrotizing myopathy of 8.3 Million person-years [41]), 250 thousand people would suffer from an ischemic stroke (assuming an incidence of 9451 per million [42]) and some people would be overrun by a car or struck by a lightning in the same year they tested positive for the virus. Considering that part of these diseases will be diagnosed before and part of them will be diagnosed after the infection, still a substantial number of new cases of even rarer diseases each year will be first diagnosed after an infection with SARS-CoV-2 [43].…”

Idiopathic inflammatory myopathies: one year in review 2022

“…The incidence of malignancy in IMNM was not higher than that of the general population. In conclusion, IMNM is a rare disease with a prevalence of one-tenth of that of IBM in Olmsted County, Minnesota (75).…”

Refractory Statin-Induced Immune-Mediated Necrotizing Myositis: Challenges and Perils in Its Management

“…Statin-induced rhabdomyolysis and IMNM are rare entities. Table 1 shows the characteristics of statin-induced myopathies [ 3 , 6 , 8 - 10 ].…”