Introduction Idiopathic inflammatory myopathies (IIM) are rare autoimmune disorders. Their clinical heterogeneity often leads to diagnostic delays, which have been associated with worse outcomes. In individuals with darker skin phototypes, cutaneous signs may be less apparent, further complicating recognition. We aimed to evaluate the association of diagnostic delay with disease activity and cumulative damage in patients with IIM. Method We conducted a cross-sectional, comparative study at a tertiary care hospital in Mexico from November 2024 to July 2025. Patients aged 18 years or older diagnosed with IIM were included and classified according to established criteria and a treating rheumatologist’s assessment. Data collected included demographics, comorbidities, skin phototype, and serology. Disease activity was measured using the myositis disease activity assessment tool which includes the Myositis Disease Activity Assessment Visual Analog Scale (MYOACT) and the Myositis Intention-to-Treat Activity Index (MITAX) and cumulative damage using the Myositis Damage Index (MDI). Patients were stratified by diagnostic delay, ≤ 5 months, and > 5 months. Statistical analysis included correlation tests and group comparisons. Results 53 patients were included, mean age of 45.3 years; 84.6% women. Dermatomyositis was the most frequent subtype (62.2%). Patients with diagnostic delay > 5 months were significantly younger (p = 0.02) and showed higher disease activity (MYOACT p < 0.001; MITAX p = 0.005) and damage (MDI extent p = 0.03). Fitzpatrick phototypes IV–V were more prevalent among patients with longer diagnostic delays (80.7% p = 0.002 vs. 51.8% p = 0.002). Conclusion Longer diagnostic delays in IIM were associated with increased disease activity, functional impairment, and disproportionate impact on younger patients and those with darker skin tones. These findings highlight the need for earlier recognition and equitable diagnostic practices in diverse populations. <Table Float="No" ID="Taba"> <tgroup cols="2"> <colspec align="justify" colname="c1" colnum="1" /> <colspec align="justify" colname="c2" colnum="2" /> <tbody> <row> <entry nameend="c2" namest="c1"> Key Points •A diagnostic delay ≥ 5 months is associated with greater accumulated damage and disease activity. • A darker skin phototype and a younger age predispose to a longer diagnostic delay. • Delayed diagnosis was associated with worse physical function. </entry> </row> </tbody> </tgroup> </Table>

Association of diagnostic delay with disease activity and cumulative damage in Hispanic patients with idiopathic inflammatory myopathies: a cross-sectional study

期刊论文
发表日期：

2026年3月10日

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Valeria Cantu-Martinez,
Miguel A. Villarreal-Alarcon,
Rebeca L. Polina-Lugo,
Emmanuel Dominguez-Chapa,
Ana C. Bardan-Inchaustegui,
Dionicio A. Galarza-Delgado,
Jesus Alberto Cardenas-de la Garza,
Rosa I. Arvizu-Rivera

摘要

Introduction

Idiopathic inflammatory myopathies (IIM) are rare autoimmune disorders. Their clinical heterogeneity often leads to diagnostic delays, which have been associated with worse outcomes. In individuals with darker skin phototypes, cutaneous signs may be less apparent, further complicating recognition. We aimed to evaluate the association of diagnostic delay with disease activity and cumulative damage in patients with IIM.

Method

We conducted a cross-sectional, comparative study at a tertiary care hospital in Mexico from November 2024 to July 2025. Patients aged 18 years or older diagnosed with IIM were included and classified according to established criteria and a treating rheumatologist’s assessment. Data collected included demographics, comorbidities, skin phototype, and serology. Disease activity was measured using the myositis disease activity assessment tool which includes the Myositis Disease Activity Assessment Visual Analog Scale (MYOACT) and the Myositis Intention-to-Treat Activity Index (MITAX) and cumulative damage using the Myositis Damage Index (MDI). Patients were stratified by diagnostic delay, ≤ 5 months, and > 5 months. Statistical analysis included correlation tests and group comparisons.

Results

53 patients were included, mean age of 45.3 years; 84.6% women. Dermatomyositis was the most frequent subtype (62.2%). Patients with diagnostic delay > 5 months were significantly younger (p = 0.02) and showed higher disease activity (MYOACT p < 0.001; MITAX p = 0.005) and damage (MDI extent p = 0.03). Fitzpatrick phototypes IV–V were more prevalent among patients with longer diagnostic delays (80.7% p = 0.002 vs. 51.8% p = 0.002).

Conclusion

Longer diagnostic delays in IIM were associated with increased disease activity, functional impairment, and disproportionate impact on younger patients and those with darker skin tones. These findings highlight the need for earlier recognition and equitable diagnostic practices in diverse populations.

Key Points

•A diagnostic delay ≥ 5 months is associated with greater accumulated damage and disease activity.

• A darker skin phototype and a younger age predispose to a longer diagnostic delay.

• Delayed diagnosis was associated with worse physical function.