Objective: To provide the first descriptive analysis of upper limb motor physiology in Niemann-Pick Type C disease (NP-C).
Methods: Fifteen patients with confirmed NP-C underwent motor physiology testing using accelerometry and surface EMG (sEMG). Tremor amplitude and frequency were quantified using accelerometry, and sEMG was examined for abnormal patterns consistent with various movement disorders.
Results: Forty-seven percent of patients had postural tremor in the upper limbs, generally bilateral, with frequencies ranging from 0.3 to 3 Hz, and an average amplitude of 1.20+/-0.98 mm. Eighty-seven percent of patients had bilateral action tremor with frequencies ranging from 2.0 to 3.7 Hz, and an average amplitude of 5.25+/-3.76 mm. sEMG revealed long but variable duration, variable amplitude muscle burst discharges during action in some patients, as well as short high frequency irregularly timed bursts in others.
Conclusions: Accelerometric findings correlated with the clinical findings were most consistent with cerebellar outflow tremors. sEMG revealed a mix of dystonic, myoclonic and choreiform movements.
Significance: These quantitative methods may serve as ancillary measures of disease pathophysiology, markers of change over time, and methods to evaluate efficacy, and side effects, of new treatments as they are developed.