Quantitative And Fiber-selective Evaluation Of Pain And Sensory Dysfunction In Patients With Parkinson’s Disease

Objective: 1. To evaluate the pain and sensory sensitivity of each class of afferent fibers in PD patients. 2. To observe the relationship of these thresholds with the presence or absence of pain, patients’ use of L-dopa. 3. To determine the effects of dopaminergic therapy on pain and sensory sensitivity.Methods: Patients with a clinical diagnosis of PD were recruited from the Department of Neurology of the Second Affiliated Hospital of Soochow University, China. Age- and sex-matched pain-free healthy controls were also recruited at our institution. PD patients were asked to describe any pain or sensory disturbances they were experiencing at the time of the study and that had already persisted for at least two months. The group of PD patients was divided into PD patients with pain(PDP) and PD patients without pain(PDNP). Medication histories were noted with respect to L-dopa exposure and patients were subdivided into those with exposure to L-dopa(ELD) and those with no exposure to L-dopa(NLD).Current perception threshold(CPT) and pain tolerance thresholds(PTT) at three frequencies, 2000 Hz, 250 Hz, and 5 Hz, to stimulate Aβ fibers, Aδ fibers, and small C-polymodal fibers, respectively, were measured in PD patients and healthy controls(refrain from taking any dopaminergic medications). We also evaluate the pain and sensory sensitivity in some of the patients after immediate levodopa therapy.Results: CPT was higher at all three frequencies and PTT was lower at 2000 Hz and 250 Hz in PD patients with pain versus healthy controls(P < 0.05). CPT was higher at 2000 Hz and 250 Hz and PTT was lower at 2000 Hz and 250 Hz in PD patients without pain versus healthy controls(P < 0.05). PD patients with pain exhibited higher CPT at 5 Hz and 250 Hz than PD patients without pain(P < 0.05). CPT was significantly higher at all frequencies and PTT was significantly lower at 2000 Hz and 250 Hz in PD patients with L-dopa exposure than in healthy controls(P < 0.05). PTT at 5 Hz was significantly higher in PD patients without L-dopa exposure than in healthy controls(P < 0.05). CPT was significantly higher at all frequencies and PTT was significantly lower at all frequencies in PD patients with exposure to L-dopa than those without(P < 0.05). Dopaminergic therapy did not affect CPT or PPT in PD patients(P > 0.05).Conclusions: Abnormal Aδ fiber- and Aβ fiber-dependent sensory inputs may exist in PD. Abnormal sensory inputs via C fibers and Aδ fibers might be associated with the presence of pain in PD. Prolonged L-dopa use may leads to neuropathy. Dopaminergic therapy failed to mitigate these sensory and pain dysfunctions.