background Detection and treatment of tardive dyskinesia depends on early and adequate diagnosis. This disabling movement disorder affects approximately 20% of schizophrenic patients who use antipsychotic and can have a devastating impact on a patient's quality of life and the compliance to use neuroleptic medication. Fine lingual movements have been reported to be an early sign of tardive dyskinesia and the tongue is the most frequently involved body region. The Abnormal Involuntary Movement Scale (aims) is most frequently used for assessing tardive dyskinesia. The reliability and sensitivity of this clinical rating scale however is highly dependent upon the experience and bias of the rater. Instrumental measurement of tardive dyskinesia may overcome these limitations.

aim To validate an instrumental technique to quantify tongue instability associated with tongue dyskinesia.

method Instrumental measurement of tongue instability was carried out in 23 psychiatric patients with antipsychotic use (11 with and 12 without tardive dyskinesia) and 7 normal controls. Subjects had to maintain a steady-state position with the tongue during 20 seconds, referenced to a target displayed on a computer screen. Instrumental tongue instability was expressed in percentage of coefficient of variation (% cv). All subjects were also screened for tongue dyskinesia (aims) by two experts in movement disorders (Kappa = 0.73) We then compared the degree of instrumental measured tongue instability with presence of tongue dyskinesia measured by the aims.

results Patients with tongue dyskinesia displayed more instrumentally measured tongue instability than patients and controls without tongue dyskinesia. Patients without tongue dyskinesia also displayed more instrumentally measured tongue instability than controls without tongue dyskinesia.

conclusion Instrumental measurement of tongue dyskinesia is a reliable and sensitive method for assessing obvious as well as subclinical dyskinesia with antipsychotic use. Instrumental measurement could be used for screening of early tongue dyskinesia.