Background/Purpose: Patients with significantly elevated creatine kinase (CK) levels are commonly referred to rheumatologists to evaluate for the presence of an idiopathic inflammatory myopathy (IIM). However, no studies have evaluated the frequency with which IIMs are encountered in this clinical scenario. The purpose of this study was to define the causes of elevated CK levels in patients referred for rheumatology consultation with a CK greater than 1,000 IU/L and to examine the clinical characteristics of these patients to determine if any distinguishing factors could be discerned.

Methods: The Vanderbilt Synthetic Derivative, a de-identified copy of over 2 million patient charts, was searched to identify patients with a CK greater than 1,000 IU/L. Other inclusion criteria were age greater than 18 and containing a document with the word rheumatology. Patients were excluded if rheumatology involvement was unrelated to the elevated CK or if there was inadequate follow-up. These criteria identified 192 patients who were assigned a diagnosis using a pre-defined algorithm. Patients determined to have an IIM were classified using the Bohan and Peter criteria for dermatomyositis (DM) and polymyositis (PM), the Griggs criteria for inclusion body myositis (IBM), or by clinical diagnosis for patients with an overlap syndrome, necrotizing myopathy, or DM/PM not meeting the above criteria. To ensure diagnostic consistency and accuracy, 10% of the charts were examined by an independent reviewer. Each chart was reviewed for pertinent demographic data and clinical characteristics.

Results: A total of 105 (55%) patients were diagnosed with an IIM. The majority of the IIM patients met Bohan and Peter criteria for DM (n=24, 13%), PM (n=41, 21%), or were diagnosed clinically with an overlap syndrome (n=28, 15%). The rest of the IIM patients were diagnosed with a necrotizing myopathy (n=2, 1%), IBM (n=1, <1%), or an IIM not meeting criteria (n=9, 5%). The non-IIM causes were drug or toxin exposure (n=16, 8%), infection (n=12, 6%), trauma (n=10, 5%), myocardial injury (n=5, 3%), hypothyroidism (n=4, 2%), muscular dystrophy (n=4, 2%), neuropsychiatric disorder (n=3, 2%), glycogen storage disorder (n=1, <1%), mitochondrial myopathy (n=1, <1%), idiopathic CK elevation (n=11, 6%), and other diagnoses (n=20, 10%). Several characteristics were found to be significantly different between IIM and non-IIM cases. Patients with an IIM were more likely to be younger (average age 48 vs. 53, p=0.04), female (71% vs. 40%, p<0.001), seen in clinic and not as an inpatient (78% vs. 44%, p<0.001), have symptoms longer than 6 months (55% vs. 29%, p<0.001), have an ANA greater than or equal to 1:40 (54% vs. 24%, p<0.001), and have a positive Jo-1 antibody (11% vs. 0%, p=0.001). Patients without an IIM had more cardiac and renal comorbidities (61% vs. 31%, p<0.001 and 16% vs. 3%, p=0.002 respectively). There was no significant difference between the CK levels of patients with IIM vs. non-IIM.

Conclusion: More than half of patients referred for rheumatology consultation with a CK greater than 1,000 IU/L were diagnosed with an IIM. Given the importance of prompt diagnosis and treatment, rapid assessment by the consulting rheumatologist for these patients is recommended.

« Back to 2015 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/causes-of-creatine-kinase-levels-greater-than-1000-iul-in-patients-referred-to-rheumatology/