Rating scales for cervical dystonia: a critical evaluation of tools for outcome assessment of botulinum toxin therapy

Botulinum neurotoxin is the therapy of choice for all forms of cervical dystonia (CD), but treatment regimens still vary considerably. The interpretation of treatment outcome is mainly based on the clinical experience and on the scientific value of the rating scales applied. The aim of this review is to describe the historical development of rating scales for the assessment of CD and to provide an appraisal of their advantages and drawbacks. The Tsui score and the Toronto Western Spasmodic Torticollis Rating Scale (TWSTRS) have been widely employed in numerous clinical studies as specific instruments for CD. The obvious advantage of the Tsui score is its simplicity so that it can be easily implemented in clinical routine. The TWSTRS allows a more sophisticated assessment of functional features of CD, but only the Tsui score includes a rating for tremor. Other benefits of the TWSTRS are the disability and pain subscales, but despite its value in clinical trials, it might be too complex for routine clinical practice. None of the rating scales used at present has been rigorously tested for responsiveness to detect significant changes in clinical status after therapeutic interventions. Moreover, clinical data support a new classification of CD leading to a differentiation between head and neck subtypes. As the current rating scales are not able to cover all these aspects of the disorder, further research is needed to develop a valid and reliable instrument which considers the most current classification of CD.