Action Tremor May Have Central Origin in Motor Neuron Disease

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Approximately 10% of the population had action tremor.
Approximately 10% of the population had action tremor.

An action tremor of a central origin as a result of a cerebellar dysfunction is highly prevalent in patients with motor neuron disease (MND), perhaps more so than tremors of peripheral origin, according to a study published in the European Journal of Neurology.

Researchers from London enrolled a total of 120 consecutive patients with MND who received care at an MND outpatient clinic for up to 12 months. Investigators collected demographic and clinical data, such as age at onset, disease duration, tremor duration, and affected body side. In addition, grip strength was assessed, and the MRC scale was used to evaluate each patient's muscle strength in the flexor carpi radialis and extensor carpi radialis muscles bilaterally.

Tremor was also assessed at rest, during posture, and during light action. Bilateral tremor recording was performed with surface electromyography and triaxial accelerometer, both with and without a variable weight load. A total of 5 patients also performed eye-blink classic conditioning to evaluate potential cerebellar involvement.

Approximately 10% of the population had action tremor. Distal postural tremor of low amplitude and constant frequency, which was bilateral and featured small asymmetry, was observed in all patients. No difference was observed between right and left side MND in terms of average grip strength (P =.475).

Patients with MND presented with fewer conditioned responses compared with healthy volunteers during eye-blink classic conditioning in each block (block 3 [P =.014], block 4 [P =.007], block 5 [P =.004], and block 6 [P =.004]). In addition, a significant positive association was found between tremor duration and kinetic tremor presence (P =.032).

Limitations of the analysis include the inability to compare patients with vs without tremor, as well as the inclusion of patients attending a single center, which may reduce the generalizability of the findings across patients with MND attending other outpatient clinics.

Findings from this small study support "the novel idea of MND as a multisystem neurodegenerative disease and suggests that action tremor is part of the condition."

Reference

Latorre A, Rocchi L, Stamelou M, et al. Tremor in motor neuron disease may be central rather than peripheral in origin [published online June 28, 2018]. Eur J Neurol. doi: 10.1111/ene.13743

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