Methodology of clinical trials for rare diseases.

Evidence from clinical trials, ideally using randomisation and allocation concealment, is essential for informing clinical decisions regarding the benefits and harms of treatments for patients. Where diseases are rare, such as in paediatric rheumatic diseases, patient recruitment into clinical trials can be a major obstacle, leading to an absence of evidence and patients receiving treatments based on anecdotal evidence. There are numerous trial designs and modifications that can be made to improve efficiency and maximise what little data may be available in a rare disease clinical trial. These are discussed and illustrated with examples from paediatric rheumatology. Regulatory incentives and support from research networks have helped to deliver these trials, but more can be done to continue this important research.