Abnormal sensory thresholds of dystonic patients are not affected by deep brain stimulation

Abstract

Background Unlike motor symptoms, the effects of deep brain stimulation (DBS) on non‐motor symptoms associated with dystonia remain unknown. Methods The objective of this study was to assess the effects of DBS on evoked experimental pain and cutaneous sensory thresholds in a crossover, double‐blind on/off study and compare these results with those of healthy volunteers (HV). Results Sixteen patients with idiopathic dystonia (39.9 ± 13 years old, n = 14 generalized) with DBS of the globus pallidus internus underwent a battery of quantitative sensory testing and assessment using a pain top‐down modulation system (conditioned pain modulation, CPM). Results for the more and less dystonic body regions were compared in on and off stimulation. The patients' results were compared to age‐ and sex‐matched HV. Descending pain modulation CPM responses in dystonic patients (on‐DBS, 11.8 ± 40.7; off‐DBS, 1.8 ± 22.1) was abnormally low (defective) compared to HV (−15.6 ± 23.5, respectively p = .006 and p = .042). Cold pain threshold and cold hyperalgesia were 54.8% and 95.7% higher in dystonic patients compared to HV. On‐DBS CPM correlated with higher Burke‐Fahn‐Marsden disability score (r = 0.598; p = .014). While sensory and pain thresholds were not affected by DBS on/off condition, pain modulation was abnormal in dystonic patients and tended to be aggravated by DBS. Conclusion The analgesic effects after DBS do not seem to depend on short‐duration changes in cutaneous sensory thresholds in dystonic patients and may be related to changes in the central processing of nociceptive inputs.

Development and Validation of the Dystonia‐Pain Classification System: A Multicenter Study

“…And based on our data, patients with longer and shorter disease durations presented similar scores in the assessments. This also supports the long‐acknowledged lack of correlation between motor symptom severity and pain intensity in movement disorders such as PD and dystonia 4,5,42,56,65 . One important aspect is that the aforementioned potential bias refers to pain classification in step 2.…”

“…Here too, pain intensity did not correlate with severity of motor symptoms. This further supports the view that motor symptoms and NMS such as pain are likely to not only depend on different mechanisms but also respond differently to treatment and have different prognoses 42,56 …”

“…This also supports the long-acknowledged lack of correlation between motor symptom severity and pain intensity in movement disorders such as PD and dystonia. 4,5,42,56,65 One important aspect is that the aforementioned potential bias refers to pain classification in step 2. The determination of pain chronicity (step 1) was based on a classic 3-month cutoff, which has been extensively validated and is recommended to classify pain as chronic.…”

“…10,50,51 The basal ganglia are responsible for the integration of motor, emotional, autonomic, and cognitive processes, probably including mood and pain. 52 Indeed, PwD have both peripheral [53][54][55][56] and central 10,57,58 sensory abnormalities, with defective processing of nociceptive stimuli integration. 59 Despite these common mechanisms behind pain and motor symptoms in dystonia, there is no linear relationship between motor symptoms and NMS in terms of response to treatment.…”

“…This further supports the view that motor symptoms and NMS such as pain are likely to not only depend on different mechanisms but also respond differently to treatment and have different prognoses. 42,56 The Dystonia-PCS created a scaffold for further classification of pain attempts, such as efforts to provide mechanism-based classifications of pain in PwD such as the use of neuropathic or nociceptive mechanistic descriptors. 15 Although this additional step is commonly attempted in clinical practice when caring for PwD and pain, sufficient information on the mechanisms of subtypes of CP in dystonia is not currently available to include them in the Dystonia-PCS.…”