WASHINGTON, D.C.–Differentiating between subgroups of myositis is a diagnostic challenge for physicians, but using some guiding principles can be helpful, an expert said during a session titled, “Muscle Biology, Myositis and Myopathies: Classification, Treatment and Outcome in Idiopathic Inflammatory Myopathies,” here at the 2012 ACR/ARHP Annual Meeting, held November 9–14. [Editor’s Note: This session was recorded and is available via ACR SessionSelect.]
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Ingrid Lundberg, MD, PhD, professor in the rheumatology unit in the department of medicine at Karolinska University Hospital in Solna, Sweden, drew from a collection of cases to offer pointers in sifting through symptoms and made suggestions that might help physicians pin down the nature of a patient’s disease as specifically as possible.
She also reviewed the latest on therapies for myositis, but said there is no “wonder drug” yet.
Patients with elevated creatine kinase (CK) and muscle weakness cannot be assumed to have myositis, she cautioned. “There are other medical conditions that have to be ruled out, and that was recognized already in the diagnostic criteria,” Dr. Lundberg said. The most important alternatives to consider are drug-induced myopathy, infection-induced myopathy, metabolic myopathy, endocrine myopathy, and muscular dystrophy, she said. “These can be excluded by clinical investigations as well as muscle biopsies,” she said.
Within myositis, doctors have to distinguish among subgroups that are illustrated in the following cases.
A 77-year-old woman presented with a history of hypothyroidism, hypertension, and Sjögren’s syndrome. At age 72, the woman had noticed a slowly progressing muscle weakness in her legs, but no pain. She had trouble walking, experiencing repeated falls and a fractured ankle.
After five years of problems, she came to the hospital and had difficulty getting up from a chair, trouble swallowing, and had atrophy of her thigh muscles. A manual muscle test—like a joint count but for the muscles—found profound weakness, with a score of 58 out of 80.
A muscle biopsy showed degenerating fibers, inflammatory cells, and rimmed vacuoles, all of which were signs of inclusion body myositis.
The biopsy can be a crucial part of the diagnosis, Dr. Lundberg said. “Muscle biopsy is essential in the diagnostic workup of myopathies, both to exclude other noninflammatory myopathies like muscle dystrophy … but also to identify subgroups like inclusion body myositis,” she said.
She also said that patients who present with weakness in the finger flexors should be considered for inclusion body myositis.