Polymyositis (PM) is a highly treatable disease. Some people recover completely, while others experience greatly diminished symptoms for long periods of time. Several years of treatment to suppress the immune system may be necessary to achieve these results.
Those who don’t recover completely may need to continue on at least a low dose of medication to control the autoimmune attack of PM throughout their lives.
Drugs that suppress the immune system are the mainstay of therapy for PM. The chart  below describes the drugs and treatments commonly used in PM, how they work and their side effects.
The first drug used in the treatment of PM is usually a corticosteroid, such as prednisone. The treatment may involve high-dose oral prednisone on a daily, every other day, or other schedule; or intermittent, short courses of intravenous corticosteroids. Sometimes, prednisone is stopped and then has to be restarted several times during the course of the disease. Prednisone is usually very effective at bringing inflammation under control, restoring for the most part the person’s strength, as well as swallowing, breathing and heart functions.
But prednisone can have many side effects, including unwanted weight gain, redistribution of fat to the face and abdomen and away from the limbs, thinning of the skin, bone loss, cataracts and psychological problems. For this reason, if long-term treatment is necessary, most doctors (and patients) want to lower the dose of prednisone as quickly as possible. This can be accomplished by adding one or more other medications to suppress the damage being caused by the immune system.
These medications include azathioprine, methotrexate, cyclosporine, cyclophosphamide — all “traditional” immunosuppressants that have been used for many years; and some newer drugs, such as mycophenolate mofetil and tacrolimus.
Although most people tolerate these medications without difficulty, they carry their own risks, such as flulike symptoms, a lowered white blood cell count (which can predispose the patient to infection) and liver toxicity. Many are associated with an increased risk of cancer.
Some with PM have responded well to intravenous infusion of antibodies culled from donors. This treatment — known as intravenous immunoglobulins, or IVIg, may seem strange in a disease that’s probably caused by an immune response in the first place, but the extra antibodies seem to “confuse” the immune system and at least temporarily alleviate the attack on muscle.
Gently progressive physical therapy, such as that taken in a swimming pool, can be very helpful in maintaining strength. Range-of-motion exercise (putting a joint through its normal movement range), particularly of the shoulders, is helpful in keeping the joints supple.
Some people may need a cane, walker or even a wheelchair during acute flare-ups of PM.
Many people eventually recover much or all of their muscle strength and function, although they may relapse and lose function if they stop taking medications.
Plasmapheresis, a “blood-cleansing” process to remove antibodies, was at one time used in PM but is rarely used today. Immunosuppressant drugs and/or IVIg treatments are now considered more effective.
|Medication or treatment||How it works||Comments|
corticosteroids prednisone tablets (Deltasone);
intravenous methylprednisolone sodium succinate
|Dampens inflammation and immune response by interfering with processing of antigens and with early triggering of T cell and B cell production and later proliferation of B cells and T cells. These cells are produced by the immune system in autoimmune diseases such as PM and DM.||Can be taken orally as prednisone and related compounds; also available for intravenous use. Many side effects with long-term, high-dose therapy, such as weight gain and redistribution of fat to face, abdomen and upper back; thinning of skin; susceptibility to infection; bone loss; muscle damage; cataracts; elevated pressures in eyes (glaucoma); psychological disturbances; high blood pressure; high blood sugar; growth slowing in children.|
|Interferes with proliferation of B cells and T cells.||Can suppress production of several types of blood cells, so cell counts must be monitored; increases risk of cancer.|
|methotrexate (Rheumatrex, Folex, Mexate)||Interferes with proliferation of B cells and T cells.||Can cause liver damage; used in higher doses to treat cancer.|
|Keeps T cells from stimulating production of more T cells and B cells (“upstream” of azathioprine and methotrexate action).||Doesn’t affect production of cells other than T cells and B cells; can cause kidney damage, infection, high blood pressure, tremor and excessive hair growth.|
|Interferes with proliferation and activity of B cells and T cells||Also used in cancer; toxic to many kinds of cells, including those of the blood and bladder; can cause sterility in both sexes.|
|Interferes with proliferation of B cells and T cells.||Can cause diarrhea, vomiting, infection (particularly with cytomegalovirus); increases risk of cancer, especially lymphomas; causes depletion of certain blood cells.|
|tacrolimus (Prograf, old name FK506)||Keeps T cells from stimulating production of more T cells and B cells (“upstream” of azathioprine and methotrexate action).||Can damage kidneys; can cause headaches, tremors and sleep difficulties; diarrhea, nausea and vomiting; high blood pressure, high blood sugar and high blood levels of potassium; increases risk of infection and lymphomas. Drug breakdown interfered with by grapefruit juice; potential for kidney damage increased by some anti-inflammatory drugs.|
|Mechanism not understood; used in arthritis, lupus, malaria; can be used to reduce steroid dosage in myositis, particularly in children.||Can treat muscle symptoms and dermatomyositis rash; can cause damage to eyes’ retinas or corneas; regular eye exams needed.|
infusion of mixed
(Gammar, Gammagard, Sandoglobulin others)
|Has complex actions on immune system, such as providing antibodies against patient’s own antibodies; interfering with immune system reaction to antibody-marked cells; interfering with blood-transported chemicals released by immune system; interfering with activation and maturation of T cells and B cells.||Doesn’t affect production of cells other than T cells and B cells; can cause kidney damage, infection, high blood pressure, tremor and excessive hair growth.|
|plasmapheresis||Removes antibodies and proteins made by the immune system from the blood and returns “cleansed” blood to patient.||Very rarely used in myositis since 1992 study showed it was no more effective than placebo; some think it’s useful when combined with immunosuppressant drugs.|