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DR. ANTHONY A. AMATO RESPONDS:
A Polymyositis and dermatomyositis are muscle diseases known as inflammatory myopathies, which are characterized by muscle inflammation and weakness. People with inflammatory myopathy may also experience arthritis, shortness of breath, difficulty swallowing and speaking, and heart arrhythmias. Onset can be in childhood to late in adult life. Data on the prevalence of polymyositis and dermatomyositis are limited, but estimates from the U.S. and Japan range between 50 and 63 cases per million people.
There are no approved medications for any of the inflammatory myopathies. However, we do use immunosuppressive therapy to treat them in practice. Corticosteroids are effective in most patients and are the first-line treatment in polymyositis and dermatomyositis. Second-line agents include methotrexate, azathioprine, mycophenolate, and intravenous gamma-globulin.
When to start a second-line agent—at the start of treatment, or only if the corticosteroids fail to produce adequate improvement—is unclear. In addition, we don't know which treatment strategy works best, and the various options are considered roughly equal. For example, no one has done a study comparing corticosteroids alone versus corticosteroids plus methotrexate, so we don't have evidence supporting one approach over the other. One needs to weigh the various risks and benefits of all these medications. Some doctors like to start with corticosteroids and see if they can taper the dose to reduce side effects; then, if the dose can't be tapered, they will add a second-line agent. Others prefer to start the two medications at the same time, which might afford faster control but also increases the risk of immunosuppression.
Speak with your neurologist about the risks and benefits of these different approaches.