Study population and eligibility criteria

A total of 116 subjects will be enrolled. Subjects should fulfil the following criteria:

A diagnosis of connective tissue disease (CTD), based on internationally accepted criteria, in one of the following categories [22–25]:

○ Systemic sclerosis

○ Idiopathic interstitial myopathy (including polymyositis/dermatomyositis)

○ Mixed connective tissue disease (MCTD)

Severe and/or progressive interstitial lung disease (ILD) associated with the underlying CTD

Chest high-resolution computed tomography (HRCT) performed within 12 months of randomisation

Intention of the caring physician to treat the ILD with intravenously administered cyclophosphamide (with treatment indications including: deteriorating symptoms attributable to ILD, deteriorating lung function tests, worsening gas exchange or extent of ILD at first presentation) and where there is a reasonable expectation that immunosuppressive treatment will stabilise or improve CTD-ILD. In individuals with scleroderma it is anticipated that patients will fulfil the criteria for extensive disease defined by Goh et al. [21]

Able to provide written informed consent

Subjects should not enter the study if any of the exclusion criteria listed in Additional file 1 are fulfilled.