Polymyositis Treatment & Management
Approach Cons >
Treatment of polymyositis (PM) is empirical because of the rarity of the disease and the paucity of randomized, controlled trials.
Prednisone is the first-line treatment of choice for polymyositis. Typically, the dose is 1 mg/kg/day, either as a single or in divided doses. This high dose is usually continued for 4-8 weeks, until the creatine kinase (CK) level returns to reference ranges. Taper prednisone by 5-10 mg on a monthly basis until the lowest dose that controls the disease is reached.
Monitor response to therapy based on improvement in muscle strength and muscle endurance and decrease in CK levels. Closely monitor patients with polymyositis for disease activity and adverse effects of corticosteroids, such as weight gain, hypertension, diabetes mellitus, osteopenia, and steroid myopathy.
Corticosteroid myopathy can occur during the course of treatment and must be distinguished from reactivation of muscle disease. The CK level is usually within reference ranges in patients with steroid myopathy. No improvement is observed with raised doses of steroids; rather, the condition worsens if the dose is increased.
Immunosuppressive agents are indicated in patients who do not improve with steroids within a reasonable period (ie, 4 wk) or in whom adverse effects from corticosteroids develop. Patients with poor prognostic indicators, such as dysphagia or dysphonia, are likely to require immunosuppressive agents. Under these circumstances, methotrexate is the second-line agent. Azathioprine, cyclophosphamide, chlorambucil, and cyclosporine have been used with varying success as second-line agents for polymyositis.Patients with inclusion body myositis usually respond poorly to corticosteroids and immunosuppressive agents.
Obtain the following baseline tests before initiating immunosuppressive therapy: liver function tests and pulmonary function, chest x-ray, TB and Hepatitis B, C testing
Intravenous immunoglobulin (IVIG) has been used for the short-term treatment of steroid-resistant cases of polymyositis. [24, 25]
The role of newer agents, such as tumor necrosis factor (TNF) inhibitors, remains unclear. Case reports describe successful use of the TNF inhibitor infliximab in refractory cases, but small clinical trials have yielded mixed results, with clinical flares occurring in some patients. [26, 27, 28, 29, 30] In a randomized controlled trial with crossover, 4 of 12 patients with refractory dermatomyositis and polymyositis responded to infliximab at a dose of 5 or 7.5 mg/kg; infliximab was well tolerated. 
A small trial of the TNF inhibitor etanercept provided encouraging results. 
The anti-CD20 monoclonal antibody rituximab may be an approach to therapy for refractory cases. The benefit of rituximab was demonstrated in the Rituximab in Myositis (RIM) study, the largest randomized trial ever completed in myositis. RIM included 200 patients with polymyositis, dermatomyositis, or juvenile dermatomyositis not controlled by corticosteroids and other immunosuppressive agents. 
The study had a placebo phase design in which half the patients received two rituximab infusions at baseline, whereas the other half received rituximab 8 weeks later. At a median of approximately 20 weeks, 83% of study subjects receiving rituximab met the International Myositis Assessment and Clinical Studies Group preliminary definition of improvement. Whether rituximab was received early or late made no significant difference in the time to achieve the definition of improvement. 
The calcineurin inhibitor tacrolimus appears to be effective, safe, and well tolerated in patients with polymyositis that is refractory to other treatments.  In a systematic review, CK levels patients decreased in all patients treated with tacrolimus, the average glucocorticoid dosage was reduced from 33.8 to 11.5 mg/day, and the majoriy of patients showed improvement in muscle strength and physical function status. However, randomized, controlled trials of tacrolimus in poymyositis have yet to be conducted. 
Mycophenolate mofetil has been reported in case reports to be effective. 
ACTH gel has shown some promise in case series with improvement in muscle as well as skin disease. Further randomized trials are required. 
Diet and Activity
Patients with polymyositis may benefit from a high-protein diet. Monitor patients to avoid excessive weight gain due to corticosteroid use.
Encourage patients with polymyositis to start a supervised exercise program early in the disease course.  During the acute stage of polymyositis, patients may benefit from heat therapy, passive range-of-motion exercises, and splints to avoid contractures.
Once acute inflammation is under control, the rehabilitation program should include active range-of-motion exercises and isometric contractions of the muscle groups. With improvement in muscle strength, patients should perform isotonic exercises with light resistance. Encourage patients to do 15-30 minute sessions of aerobic exercise when the disease is inactive.
A neurologist or rheumatologist is the primary consultant. Consultation may also be required with the following specialists: