Therapeutical trial in patients with idiopathic polymyositis and dermatomyositis is proposed. The study will investigate the safety and efficacy of combined methotrexate + glucocorticoids treatment compared with glucocorticoids alone.

This will be a randomised, open-label, assessor-blind, international multicenter trial, performed in several European centres interested in research on inflammatory myopathies.

A total number of 50 patients with polymyositis/dermatomyositis will be randomised into two groups (1: Methotrexate + glucocorticoids and 2: Glucocorticoids only). Patients will be equally distributed between the two groups providing 25 patients per treatment arm. The randomisation will be based on random numbers generated by a computer program. After being enrolled in the study, the patients will receive 12 months of therapy followed by a 12-month follow-up period.

The primary endpoint is the total dose of glucocorticoids (calculated in mg/kg weight), which will be administered for 12 months between baseline and the end of treatment.

There are several of secondary objectives, which will be pursued during and after the trial. Disease activity and damage will be prospectively assessed by the newly developed tools for myositis disease activity (MYOACT and MITAX) and for myositis damage (MYODAM and MDI. Other secondary objectives comprise: global assessment of activity and damage by patients and by physician, muscle endurance, muscle strength by manual muscle testing, enzyme levels, glucocorticoid related side effects, functional ability measured by HAQ, quality of life by SF-36, and number of patients with treatment failures. The other aims will also include (i) search for reliable prognostic parameters in the further prognosis of patients with inflammatory myopathies and (ii) studies on the pathogenic aspects of inflammatory myopathies. The investigations of serum, lymphocytes, muscle tissue and MRI will be organized. DNA and RNA will be stored for future genetic studies.

Patients with definite or probable polymyositis or dermatomyositis diagnosed according to diagnostic criteria will be enrolled. They will have disease activity that according to physician's own judgement requires high dose immunosuppressive treatment (based on clinical assessment of weakness, elevation of muscle enzymes and, if available, on magnetic resonance imaging findings). Patients should be previously untreated with the exception of glucocorticoid treatment up to 8 weeks.

Patients with other than primary idiopathic polymyositis or dermatomyositis, such as drug-induced myositis, myositis in association with other connective tissue disease, inclusion body myositis, malignancy related myositis, and juvenile dermatomyositis will be excluded.

All patients will start with prednisone 1 mg/kg/day and the dose will be tapered if patients meet definition of improvement, which has been proposed by IMACS group. Methotrexate/placebo will be administered orally, once weekly, with a starting dose 10 mg. This will be increased gradually to 25 mg/week if tolerated by week 5. Patients will be first assessed after 2 weeks and than monthly for a period of 48 weeks. There will be a follow-up after a further 1 year in order to find out the impact of the early treatment on the long-term disease outcome.

All efficacy analyses will be performed using intention-to-treat population (ITT). In addition, the primary and secondary variables will be analysed using the per-protocol population, which will contain all patients in the ITT population, who also reached Week 48 of treatment without any major protocol violations. The safety population, which will contain any patient who received at least one dose of study drug, will be used for all safety analyses.