The utility of temporal discrimination threshold testing in different adult-onset primary torsion dystonia phenotypes

Bradley, D and Mulrooney, N and Whelan, R and Reilly, R and Hutchinson, S and Molloy, F and Hutchinson, M
Movement Disorders, 25: S231–S232, 2010

AOPTD is autosomal dominant with significantly reduced penetrance. Sensory abnormalities are a marker of basal ganglia dysfunction in these patients and may be used as an endophenotype. The temporal discrimination threshold (TDT) is the shortest time interval at which two stimuli are detected to be asynchronous. The comparative utility of TDT testing in different types of AOPTD is of interest in planning genetic studies. We aimed to examine the frequency of abnormal temporal discrimination thresholds (TDTs) in various adult-onset primary torsion dystonia (AOPTD) phenotypes. TDTs were examined in 38 cervical dystonia (CD), 13 writer’s cramp (WC), 12 spasmodic dysphonia (SD), 10 blepharospasm (BEB) and 4 musician’s dystonia patients as well as 51 healthy control participants. Measurements were taken using visual (two LED lights), tactile (nonpainful electrical stimulation) and mixed (one LED, one electrical) tasks. The mean TDT in controls <50 years was 24.45 ms and >50 years was 30.87 ms. The upper limit of normal was defined as control mean +2.5 SD. Abnormal TDTs were seen in 37/38 (97%) of CD, 11/13 (85%) of WC, 10/12 (83% of SD), 9/10 (90%) of BEB patients and 2/4 musicians. None of the control subjects had abnormal TDTs. The frequencies of abnormalities in CD, WC, SD and BEB patients are comparable. Musicians may represent a different or heterogeneous pathological group.