Laboratory Test Abnormalities are Common in Polymyositis and Dermatomyositis and Differ Among Clinical and Demographic Groups

Abstract

Objective:Given the difficulties regarding the interpretation of common laboratory test results in polymyositis (PM) and dermatomyositis (DM) in clinical practice, we assessed their range of abnormalities, differences among phenotypes and interrelationships in a large referral population.Methods:We retrospectively assessed 20 commonly measured blood laboratory tests in 620 well-defined PM/DM patients at different stages of illness and treatment to determine the frequency, range of abnormalities and correlations among clinical, gender, racial and age phenotypes.Results:Myositis patients at various stages of their disease showed frequent elevations of the serum activities of creatine kinase (51%), alanine aminotransferase (43%), aspartate aminotransferase (51%), lactate dehydrogenase (60%), aldolase (65%) and myoglobin levels (48%) as expected. Other frequent abnormalities, however, included elevated high white blood cell counts (36%), low lymphocyte counts (37%), low hematocrit levels (29%), low albumin levels (22%), high creatine kinase MB isoenzyme fractions (52%), high erythrocyte sedimentation rates (33%) and high IgM and IgG levels (16% and 18%, respectively). Many of these tests significantly differed among the clinical, gender, racial and age groups. Significant correlations were also found among a number of these laboratory tests, particularly in the serum activity levels of creatine kinase, the transaminases, lactate dehydrogenase and aldolase.Conclusion:Laboratory test abnormalities are common in PM/DM. Knowledge of the range of these expected abnormalities in different myositis phenotypes, gender and age groups and their correlations should assist clinicians in better interpretation of these test results, allow for a clearer understanding what level of abnormality warrants further evaluation for liver or other diseases, and may avoid unnecessary laboratory or other testing.

Electrophysiological and Clinical Examination of Polymyositis: A Retrospective Analysis

“…CRD is 1 type of spontaneous potential and occurs in 25% of patients with PM. These results were similar to those previously reported 16 with the exception of CRDs, which occurred less frequently (6.45%) than reported. 17 We found that prolonged insert potential occurred in 15.88% of muscles, and spontaneous potential occurred in 68.8% of muscles.…”

“…16 Fasciculation potential was previously reported in 10% of cases. CRD is 1 type of spontaneous potential and occurs in 25% of patients with PM.…”

Serum Transaminases Are Frequently Elevated at Time of Diagnosis of Idiopathic Inflammatory Myopathy and Normalize With Creatine Kinase

“…5 Transaminases catalyze the transfer of an amino group from an amino acid to a keto acid 2 and are found predominantly in the liver and at smaller concentrations in skeletal muscle, myocardium, kidney, pancreas, lung, spleen, and red blood cells. 6,7 Of note, a retrospective analysis of 61 myositis patients demonstrated a linear relationship between log serum CK and log ALT (r = 0.78, r 2 = 0.59, P G 0.001) 6 and reported that the ALT level can be predicted based on the rise in CK. This Previous studies have shown a positive correlation between levels of CK and ALT.…”

2016 American College of Rheumatology/European League Against Rheumatism Criteria for Minimal, Moderate, and Major Clinical Response in Juvenile Dermatomyositis: An International Myositis Assessment and Clinical Studies Group/Paediatric Rheumatology International Trials Organisation Collaborative Initiative

“…For muscle enzymes, the most abnormal enzyme at baseline is used. The enzyme range was calculated based on 90% range of enzymes from natural history data (5;36), and for creatine kinase is 15 times the upper limit of normal; for aldolase is six times the upper limit of normal, and for lactate dehydrogenase, aspartate aminotransferase, and alanine aminotransferase is three times the upper limit of normal. An Improvement Score is assigned for each core set measure based on the absolute percent change.…”