Participants will be randomly assigned to receive either 3 mg/kg body weight of infliximab or a placebo (inactive substance) by infusion through a vein over 2 hours. The infusions will be given at the beginning of the treatment period (week 0) and at weeks 2, 6 and 14. At week 16, strength will be assessed by manual muscle testing. Patients who improved with treatment will continue with the same infusion dose on weeks 18, 22, 30, and 38. Those who do not improve will be assigned by random allocation to receive either 5 mg/kg body weight or 10/mg/kg body weight of infliximab on weeks 18, 22, 30 and 38. Those who did not improve who were previously on the placebo infusion will receive an extra dose of either 5 mg/kg or 10 mg/kg body weight of infliximab on week 16, while those patients who were previously on 3 mg/kg body weight of infliximab who failed to meet the improvement criteria will receive an infusion containing no medication on week 16. Patients will be admitted to the hospital for infusions at weeks 0, 14 and 38; the rest will be given on an outpatient basis. After the 38th week, all infusions will be stopped and patients will be assessed on the 40th week.