Objective:

To explore demographic and racioethnic factors contributing to clinical phenotype and treatment response in patients with anti-HMGCR-positive immune-mediated necrotizing myopathy (IMNM).

Background:

IMNM is a rare inflammatory condition typically related to statin exposure. The demographic and racioethnic factors contributing to phenotypic heterogeneity and differential treatment responses in patients with IMNM are not fully understood.

Design/Methods:

This exploratory retrospective study investigated 25 patients with a diagnosis of IMNM seen between 2017 and 2025, including their demographic and disease-specific characteristics. We explored the number of immune therapy escalations (defined as addition of therapy or increase in dose/frequency) and hospitalizations related to IMNM.

Results:

We identified 25 patients with IMNM, with a mean age of 59.9 years±12.8 and of whom 48% were female. The overall mean time to diagnosis was 9.7±11.0 months, ranging from 7.9±12.44 months for White patients (7/25) to 12.1±11.43 months for Hispanic patients (8/25). At presentation, mean creatine kinase levels were higher in Black (11,000±1,414 U/L) and Asian (10,332±4,417 U/L), compared to White patients (6,528±2,730). Mean anti-HMGCR antibody levels were highest in Asian (280±97.3 U) and Hispanic (264.4±125.0 U) patients, compared to White (149±55.1 U) and Black patients (141±42.4 U). Therapy escalations were more frequent in male patients (2.91±2.21 vs. 1.36±1.03), patients under the age of 50 (3.20±2.17 vs. 1.94±1.92), and in Hispanic patients (2.89±1.83 vs. 0.75±0.50 in Asian patients). Hospitalizations related to IMNM were highest among Black patients (100%, 2/2), followed by Hispanic (50%, 5/10) and Asian patients (50%, 2/4), compared to 38% of White patients (3/8). These trends did not reach statistical significance (p > 0.05).

Conclusions:

This explorative study identified trends suggesting that demographic and racioethnic factors may influence phenotype and treatment response in IMNM. A larger study currently in process may elucidate these further.