Normal Creatine Kinase in Idiopathic Inflammatory Myopathies: Disease Characteristics and Outcomes
Authors' conclusion
Normal CK levels are common in IIM, especially in DM, and do not exclude active muscle disease. CK functions as a longitudinal biomarker across IIM, with performance varying by disease subset and baseline CK, supporting nuanced clinical interpretation.
Study context
- Population
- Patients with refractory adult idiopathic inflammatory myopathies (IIM) in the Rituximab in Myositis (RIM) trial
- Participants
- 143 patients
- Comparison
- Patients with normal creatine kinase (CK) vs patients with elevated CK
- NORMAL CKn = 53
Methodological detailsmyositis core set measures collected every 4 weeks for 44 weeks, linear mixed models
- Myositis core set measures collected every 4 weeks for 44 weeks
- Linear mixed models
Primary result
As reported in the abstract
Normal CK · baseline
Patients with normal CK
53
37%
Further findings
White
P < 0.01
Female
P = 0.08
| Outcome | NORMAL CK | ELEVATED CK | P value |
|---|---|---|---|
| Age | 52 ± 10 | 49 ± 12 | P = 0.07 |
Myositis subtype
- Normal CK most frequent in dermatomyositis, whereas elevated CK was common in necrotizing myopathy (p< 0.001)
Baseline correlation of CK with physician assessment and muscle disease activity
- Elevated CK: CK correlated with physician assessment
- P = 0.01
- Elevated CK: CK correlated with muscle disease activity
- P = 0.001
- Normal CK: no baseline associations observed, despite active disease
Longitudinal associations of CK with all core set measures (CSMs) (linear mixed models) · 44 weeks
- Significant longitudinal associations with all CSMs, regardless of baseline CK status
- P < 0.001
- Associations more robust in polymyositis and in elevated baseline CK, attenuated in dermatomyositis and antisynthetase syndrome among patients with baseline normal CK
Original publication
Normal Creatine Kinase in Idiopathic Inflammatory Myopathies: Disease Characteristics and Outcomes. Joint Bone Spine. Published 31 October 2026. doi:10.
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