Measuring disease in dermatology: studies of objective and subjective methods

Abstract

Itch lies second only to disturbance of body image as a reported symptom in dermatology. This study started by concentrating on improving the measurement of itch. Itch has a paired physical response, scratch. The pairing can be exploited: preliminary work by this unit had validated the use of wrist-worn movement-measuring machines called ‘accelerometers’ to measure itch-related movement (scratch and rub). The first part of this research developed use of these machines. Simple accelerometers (‘Actiwatch Plus’) were used to observe the pattern of variation of itch over clusters of nights and in different conditions. The accelerometer scores were able to identify controls’ scores from those with itchy disease. Considerable variation (56%) was discovered in objective score between subject and considerable variation was noted (46%) even within subject. More complex accelerometers, (‘DigiTrac’) which could potentially specifically identify itch-related movement on the basis of frequency of action derived from Fast Fourier Transform (FFT), were validated against the ‘gold standard’ measurement of itch-related movement, directly observed movement (via infra red video recording). It was necessary to characterise the ‘frequency of action’ of itch on video and, as an aside, the characteristics of human itch-related movement were compared to other mammals’ itch-related movement ‘frequency of action’. The ‘frequency of action’ and video data was used to enrich the DigiTrac readouts to improve specificity of itch-related movement detection. During the accelerometer studies, an unexpected finding came to light: objective score of itch was not related to subjective score. To try to explain the lack of relationship, a 42 day longitudinal study of atopic dermatitis patients’ subjective and objective scores was undertaken. The results demonstrated autocorrelation for subjective scores, but not for the objective scores but still did not fully explain the lack of relationship. In an effort to explain the disconnect between subjective and objective scores a second tranche of experiments and the second part of this research interrogated whether the methods with which we measure disease as a whole in dermatology are robust. One study investigated whether the way patients are asked about subjective symptoms in general was resistant to the effects of focusing and framing bias. The results were reassuring as they suggested that the commonly used and recommended symptom scoring systems were robust in the face of bias. In order to assess whether perspective or perception of disease explained the disconnect, a study was designed in collaboration with the Edinburgh College of Art. A series of computer-generated images of different psoriasis severities were created and used to assess how doctors and patients assessed disease-extent. This study showed that, whilst each group had a naturally divergent opinion of extent of disease, by scoring disease using the models it was possible to unify the perspective and perception of extent. Finally, an exploratory study to reduce recall bias to a minimum, in case this had caused the disconnect between objective and subjective, was undertaken. This employed a novel questionnaire, the Day Reconstruction Method.