Causes of creatine kinase levels greater than 1000 IU/L in patients referred to rheumatology.

Patients with severely elevated creatine kinase (CK) concentrations 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 Vanderbilt Synthetic Derivative, a de-identified copy of over 2 million patient records, was searched to identify adult patients with a CK greater than 1000 IU/L who had been evaluated by a rheumatologist. Each patient was assigned a diagnosis using a pre-determined algorithm. The records were then reviewed for pertinent demographic data and clinical characteristics. A total of 192 patients were included for analysis. Of these patients, 105 (55 %) were diagnosed with an IIM. The non-IIM causes were drug/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 %), metabolic myopathy (n = 2, 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. In particular, patients with an IIM were more likely to be female, have a positive ANA, have interstitial lung disease, and have proximal, symmetric weakness. This study found that approximately half of patients referred to our division of rheumatology with a CK greater than 1000 IU/L were diagnosed with an IIM. Given the importance of prompt diagnosis and treatment of these disorders, rapid assessment by the consulting rheumatologist for these patients is recommended.