Improved device for measuring scratching activity in patients with pruritus

Pruritus is an inherently subjective perception that cannot be quantified. However, in trials of new therapies for pruritus, it is necessary to base assessments of therapeutic efficacy on objective quantitative criteria. This can be achieved by measuring the behavioural consequence of pruritus, scratching activity, and using an index of scratching activity as an efficacy endpoint. A portable device to monitor scratching activity in patients with pruritus is described. The key feature of this device is a piezo-element attached to a fingernail. Vibrations of the fingernail in the act of scratching induce electrical impulses in the piezo-element. Electrical signals from the device are filtered and measured. The measurements, which are not absolute, have nevertheless been shown to provide an objective index of scratching activity that is independent of arm and hand movements. An advantage of the device is that recordings can be made while the patient is in a normal, non-hospital environment, thereby obviating effects of change of environment (e.g. hospitalisation) on the intensity of pruritus. Application of the device enables data on scratching activity during periods of treatment with a test drug and with a placebo to be compared in individual patients.