Most clinicians agree that glucocorticoids (e.g., prednisone, 1 mg/kg, as a single daily dose orally, or intravenously) are a reasonable first therapy for both PM and DM. The response to treatment is monitored by testing of strength and measurement of CK (not by following the erythrocyte sedimentation rate [ESR]). In patients who respond clinically, the serum CK decreases before the weakness subsides; with relapse, the serum CK rises before weakness returns. Once the CK level normalizes and strength improves, typically several weeks or longer, one approach is to reduce the dosage gradually—by no more than 5 mg every 2 weeks—toward 20 mg daily. It is then appropriate to attempt to control the disease with an alternate-day schedule with double this amount (i.e., prednisone, 40 mg every other day) so as to reduce the side effects of the drug. After cautious reduction of prednisone over a period of 6 months to 1 year or longer, the patient can usually be maintained on doses of 7.5 to 20 mg daily, with the aim of eventual discontinuation of the drug. Corticosteroids should not be discontinued prematurely, for the relapse that may follow is often more difficult to treat than the original illness. Some clinicians prefer to add an immunosuppressive agent at this time rather than wait for failure of glucocorticoids or as a means of reducing steroid dependence, as discussed below.
In acute and particularly severe cases, treatment may be facilitated by the use initially of high-dose methylprednisolone (1 g intravenously each day for 3 to 5 days). This form of treatment should be regarded as a temporary measure until oral prednisone or a more fast-acting treatment becomes effective.
Alternatively, or sometimes in tandem with this approach in severe cases, intravenous immunoglobulin (IVIg) or plasma exchanges may be instituted. In patients with DM who respond poorly to corticosteroids and other immunosuppressants or are severely affected early on, the addition of IVIg infusions often proves helpful, although several courses of treatment at monthly intervals may be required to achieve sustained improvement. In several controlled studies of small numbers of patients with DM, practically all showed improvement in muscle strength and in skin changes, and a reduction in CK concentration (see Dalakas 1997; Mastaglia et al). PM has also been reported to respond favorably to treatment with IVIg, but the evidence is less certain. Further controlled studies are required to corroborate these reports and to establish, in both PM and DM, the optimal doses and modes of administration. It is noteworthy from our experience that IVIg has seldom been effective in PM or DM when used alone or as initial therapy. These options are discussed in the review by Dalakas (2015). The proper use of these treatments in crossover cases with connective tissue disease has not been established.