Objectively measured motor activity in schizophrenia challenges the validity of expert ratings

Motor symptoms are frequent in schizophrenia and relevant to diagnosis. They are usually assessed by clinical observation and ratings based on psychometric scales. However, investigations with quantitative measurements are rare. To understand the relationship between the objective parameters of a quantitative motor activity measurement and the items related to motor symptoms of the Positive and Negative Syndrome Scale (PANSS), 55 schizophrenia patients were studied with 24-h continuous wrist actigraphy. Activity level, movement index, and mean duration of uninterrupted immobility periods were analyzed for wakeful periods. Actigraphic parameters were strongly inter-correlated. High PANSS negative syndrome subscale scores predicted low activity levels. Single PANSS items, such as suspiciousness, hallucinatory behavior, and emotional withdrawal, contributed largely to the variance in activity level and movement index. Age, gender, medication, and duration of illness had no significant impact on the actigraphic parameters. Interestingly, correlations between the specific motor symptoms of the PANSS and the actigraphic parameters were only found as a non-significant trend. We conclude that the objectively measured quantity of movement is related to the clinically assessed negative syndrome in schizophrenia. In contrast, PANSS items related to psychomotor behavior imprecisely reflect real quantitative motor activity.