Measurement of ataxic symptoms with a graphic tablet: standard values in controls and validity in Multiple Sclerosis patients

Aim of our study was to find a specific measure for the intensity of upper limb tremor and other ataxic symptoms in Multiple Sclerosis (MS) patients, and to establish standard values and test quality parameters. Three hundred and forty-two consecutive patients with different symptoms in the upper limbs (upper motor neuron symptoms, cerebellar upper limb ataxia, and/or sensory deficits in the upper limbs) and 140 healthy controls took part in the study. All patients and controls had to trace over a 25 cm high figure ‘8’ on a graphic tablet, to tap with the stylus on the tablet and to perform the nine-hole-peg test (9HPT). Patients were additionally examined using clinical standard scales to classify motor dysfunctions of the upper limbs. One hundred and eighty-nine patients and 27 controls were tested twice to investigate the test reliability. Kinematic analysis of the tablet data was performed by kernel estimators, oscillatory activity by spectral analysis. Total power in the 2–10 Hz band was very specific for ataxia versus other motor symptoms. Tapping and 9HPT could well distinguish patients from controls, and patients with predominant motor neuron or cerebellar symptoms from patients with predominant sensory dysfunctions. Mean drawing error did not differ between motor and sensory dysfunctions. The test–retest reliability was similarly high for both spectral analysis and 9HPT.