Tremor in chronic inflammatory demyelinating polyneuropathy: Proof of unifying network model for dystonia

Proprioceptive Modulation of Pallidal Physiology in Cervical Dystonia

BACKGROUND

There is a growing body of evidence suggesting that botulinum toxin can alter proprioceptive feedback and modulate the muscle-spindle output for the treatment of dystonia. However, the mechanism for this modulation remains unclear.

METHODS

We conducted a study involving 17 patients with cervical dystonia (CD), seven of whom had prominent CD and 10 with generalized dystonia (GD) along with CD. We investigated the effects of neck vibration, a form of proprioceptive modulation, on spontaneous single-neuron responses and local field potentials (LFPs) recorded from the globus pallidum externus (GPe) and internus (GPi).

RESULTS

Our findings demonstrated that neck vibration notably increased the regularity of neck-sensitive GPi neurons in focal CD patients. Additionally, in patients with GD and CD, the vibration enhanced the firing regularity of non-neck-sensitive neurons. These effects on single-unit activity were also mirrored in ensemble responses measured through LFPs. Notably, the LFP modulation was particularly pronounced in areas populated with burst neurons compared to pause or tonic cells.

CONCLUSION

The results from our study emphasize the significance of burst neurons in the pathogenesis of dystonia and in the efficacy of proprioceptive modulation for its treatment. Moreover, we observed that the effects of vibration on focal CD were prominent in the α band LFP, indicating modulation of pallido-cerebellar connectivity. Moreover, the pallidal effects of vibration in GD with CD involved modulation of cerebro-pallidal θ band connectivity. Our analysis provides insight into how vibration-induced changes in pallidal activity are integrated into the downstream motor circuit. © 2023 International Parkinson and Movement Disorder Society.

The effect of tremor on disability assessment in chronic inflammatory demyelinating polyradiculoneuropathy

Tremor in chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) is common, often unresponsive to treatment, and may contribute to disability. We aim to investigate whether tremor is associated with disability as measured in daily practice and clinical trials, independent of other impairments. We included 76 CIDP patients in this cross-sectional study. We assessed tremor with the Tremor Research Group essential tremor rating assessment scale (TETRAS) and the Fahn-Tolosa-Marin clinical rating scale (FTM). Disability was measured with the inflammatory Rasch-built overall disability scale (I-RODS) and the adjusted Inflammatory Neuropathy Cause and Treatment disability scale (INCAT-DS, categorized separately in arm score, or total score). Impairments including strength, sensory impairment, and fatigue were measured using specific impairment scales. We tested whether "the presence of a clinically relevant tremor" (based on TETRAS and FTM) or "tremor severity" (FTM part B sum score) was associated with disability scores (I-RODS, INCAT-DS total score, and INCAT-DS arm score), independent of the impairment scores, using multivariate regression. Both "the presence of a clinically relevant tremor" and "tremor severity" were significantly associated with disability measured by the INCAT-DS (arm score and total score), but not the I-RODS, independent of strength, sensory impairment, and fatigue. The explained variances were low. Clinically relevant tremor can (partly) explain disability in CIDP, as measured with the INCAT-DS, independent of muscle strength, sensory deficits, and fatigue. To assess disease activity in CIDP patients with tremor, both impairment and disability outcomes should be assessed, as disability is caused partly by tremor while the effect of immunotherapy on tremor seems limited.