Background/Purpose: Asymptomatic or mildly symptomatic patients with moderate creatine kinase (CK) elevation are commonly referred to rheumatologists. In patients without a clearly established diagnosis, the significance of the CK elevation and long term outcomes are unclear and there is lack of data to help rheumatologists to counsel these patients. The purpose of this study was to examine the outcomes of patients with moderate CK elevation of unclear etiology and identify possible predictors of CK normalization and symptom resolution.

Methods: Retrospective chart review of asymptomatic or mildly symptomatic patients with moderate (250-1000 U/L) CK elevation who were referred to a rheumatologist for that reason, in a tertiary health system. Patients with known inflammatory myopathy, elevated troponin, cardiovascular disease, epilepsy or rhabdomyolysis were excluded. Patients with an established diagnosis within the first two visits with the rheumatologist were also excluded. Comparisons between groups were tested using two-sample t-tests, Wilcoxon rank sum tests, or Kruskal-Wallis tests, and Pearson’s chi-square or Fishers exact tests, as appropriate.

Results: 62 patients were included of which 67.7% were male, 95.2% Caucasian, with median CK 368 U/L at baseline, median highest CK 602 U/L and median follow up of 7 years (interquartile range 5 to 8 years).  At the end of the observation period, 2 patients (3.2%) were diagnosed with inflammatory myopathy, 36 patients (58.1%) were thought to have elevated CK due to medications (mostly cholesterol lowering medications), 5 patients (8.1%) were classified as “other” (race, exercise) causes and for 19 (30.6%) patients there was no established cause for the elevated CK. There were no differences between the outcome groups regarding demographics, median CK or symptoms at baseline. In 27 patients (43.5%) CK normalized at follow-up. Patients with normalized CK were older (median age 66 vs. to 56 years, p= 0.03) and had lower CK levels (median CK 306 vs. to 403 U/L, p= 0.009) at baseline compared to patients whose CK remained elevated. Of the 56 patients with symptoms at baseline 28 (50%) became symptom-free at follow up; absence of muscle weakness was associated with resolution of the symptoms in follow-up (92.3% vs. 67.9%, p = 0.026). In the 36 patients with CK elevation due to medications, CK normalized in 19 (52.8%) and symptoms subsided in 20 (55.6%) patients at follow-up. In the 19 patients with CK elevation of unknown etiology, CK normalized in 6 (31.6%) and symptoms subsided also in 6 (31.6%) patients at follow-up.

Conclusion: In patients with asymptomatic or mildly symptomatic moderate CK elevation, the main etiology is lipid lowering medicines but in a substantial proportion the etiology remains unclear. In older patients and patients with lower CK at baseline it is more likely that CK normalizes in follow-up; patients without weakness as the main symptom at baseline were more likely to become asymptomatic at follow-up. These are encouraging findings that can help rheumatologists counsel these patients on their long term prognosis.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/long-term-outcomes-of-patients-with-moderate-creatine-kinase-ck-elevation-seen-in-a-rheumatology-clinic/