It’s amazing how far we’ve come—but how far we have to go,” reflected moderator Mary E. Cronin, MD, professor of medicine at the Medical College of Wisconsin in Milwaukee. She was echoing the sentiments of another presenter at the symposium, “Idiopathic Inflammatory Myopathies: Current Concepts,” at the 2009 ACR/ARHP Annual Scientific Meeting in Philadelphia. Paul H. Plotz, MD, chief of the Arthritis and Rheumatism Branch of the National Institute of Arthritis, Musculoskeletal, and Skin Diseases in Bethesda, Md., had just summarized a history of idiopathic inflammatory myopathies (IIM) from 1863 to the present and concluded, “a coherent model of pathogenesis has not yet emerged, a top cytokine has not been identified, and I think we have a long way to go.”
In the meantime, according to top investigators, clinicians can rely on foundational diagnostic criteria, track empirical data from investigations of new agents, and look to cross-disciplinary and international collaborations to further our understanding of this complex and heterogeneous group of diseases.
Evaluation: Back to Basics
Robert L. Wortmann, MD, professor of medicine at Dartmouth-Hitchcock Medical Center in Lebanon, N.H., reviewed diagnostic tools for evaluating patients with muscle weakness. Quite often, a thorough history and physical allows clinicians to differentiate between a nerve problem, a muscular problem, or a neuromuscular junction problem, he stated. The basic rules, he said, “hold very well in the clinic, and I ask you not to just blow them off.” Myopathic problems, he noted, are proximal and symmetric, with the remainder of the neurologic exam normal. In contrast, although neuropathic problems can cause proximal muscle weakness, they also cause distal and asymmetric weakness as well as other neurologic abnormalities.
The timed stand test (in which the patient is asked to stand from a chair without using hands for assistance) is an easy test for quantifying lower extremity proximal weakness and is reproducible over time. In patients with proximal muscle weakness, additional findings of high levels of creatine kinase (CK), fatigue, morning stiffness, and weight loss point to differential diagnosis of an inflammatory myopathy, validating the criteria first devised by Bohan and Peter in 1975.
Laboratory tests, especially the muscle enzymes such as CK, aldolase, and succinyl-CoA:3-ketoacid CoA transferase (SCOT), should be measured. “Be aware,” Dr. Wortmann cautioned, “that at any one time, about a third of the population may have a high CK.” High levels can be due to multiple causes, such as racial differences (normal CK levels for black men are at the upper limit of normal in other racial groups); trauma; exercise; and recreational (alcohol, cocaine) and prescribed (statins, HIV medication) drugs.