  BACKGROUND: Randomized controlled trials (RCTs) are the gold standard design
of clinical research to assess interventions. However, RCTs cannot always be
applied for practical or ethical reasons. To investigate the current practices
in rare diseases, we review evaluations of therapeutic interventions in
paediatric multiple sclerosis (MS) and Creutzfeldt-Jakob disease (CJD). In
particular, we shed light on the endpoints used, the study designs implemented
and the statistical methodologies applied.
  METHODS: We conducted literature searches to identify relevant primary
studies. Data on study design, objectives, endpoints, patient characteristics,
randomization and masking, type of intervention, control, withdrawals and
statistical methodology were extracted from the selected studies. The risk of
bias and the quality of the studies were assessed.
  RESULTS: Twelve (seven) primary studies on paediatric MS (CJD) were included
in the qualitative synthesis. No double-blind, randomized placebo-controlled
trial for evaluating interventions in paediatric MS has been published yet.
Evidence from one open-label RCT is available. The observational studies are
before-after studies or controlled studies. Three of the seven selected studies
on CJD are RCTs, of which two received the maximum mark on the Oxford Quality
Scale. Four trials are controlled observational studies.
  CONCLUSIONS: Evidence from double-blind RCTs on the efficacy of treatments
appears to be variable between rare diseases. With regard to paediatric
conditions it remains to be seen what impact regulators will have through e.g.,
paediatric investigation plans. Overall, there is space for improvement by
using innovative trial designs and data analysis techniques.
