Neuropathic pain in adult Myotonic Dystrophy type 1. Presence of small and large fibre neuropathy?

Background: Myotonic Dystrophy type 1 (DM1) is an inherited neuromuscular disorder affecting multiple organs. There is an increasing awareness of chronic pain in DM1. In this cross-sectional study, we investigated symptoms of neuropathic pain and small and large fiber neuropathy in the adult form of DM1. We also studied if neuropathy was related to the number of CTG repeats, disease duration and other clinical DM1 symptoms, and investigated if skin biopsy tests for small fiber neuropathy differed in the DM1 group compared to reference values from healthy controls.Methods: 20 genetically verified DM1 adult patients were included in the study. Pain descriptions, neurologic examination and objective investigations of the peripheral nerve system by quantitative sensory testing, skin biopsies and neurography were conducted. Statistical analyses of group differences and frequencies were performed.Results: Six patients (30%) out of 20 patients with DM1 described neuropathic pain, and three of these had objective findings on both small and large fiber neuropathy, as well as clinically sensory findings. Together, large and/or small fibre neuropathy is present in 50% of the patients with DM1. The intra epidermal nerve fiber density was significantly lower (p= <0.001, Cohen`s d = 1.2) in the 20 patients with DM1 (mean 8.16, SD: 2.28) compared to a reference group (N = 106, mean 12.43, SD: 4.59). Patients with large fiber neuropathy had significantly lower muscle strength (p = 0.01, Cohen`s d = 1.6, mean difference 0.4, CI: 0.7 - 0.1) than patients without large fiber neuropathy.Conclusion: Symptoms of neuropathic pain was more frequent in patients with DM1 compared to the general population. Intra epidermal nerve fiber density was significantly lower in the DM1 group than in a sample of healthy controls. Neuropathy may be a mechanism of pain in DM1.

Large-Fiber Neuropathy in Parkinson’s Disease: Clinical, Biological, and Electroneurographic Assessment of a Romanian Cohort

(1) Background: Increased attention has lately been given to polyneuropathy in Parkinson’s Disease (PD). Several papers postulated that large-fiber neuropathy (PNP) in PD is related to vitamin B12 deficiency and L-Dopa exposure. (2) Methods: Using a cross-sectional, observational study, we evaluated 73 PD patients without a previously known cause of PNP using clinical scores (UPDRS II and III and Toronto Clinical Scoring System), biological evaluation of vitamin B12 and folic acid, and nerve conduction studies to assess the prevalence and features of PNP. (3) Results: The prevalence of PNP was 49.3% in the study group. In the L-Dopa group, the frequency of PNP was 67.3% as compared to PNP in the non-L-Dopa group, where one subject had PNP (χ2 = 23.41, p < 0.01). PNP was predominantly sensory with mild to moderate axonal loss. Cyanocobalamin correlated with L-Dopa daily dose (r = −0.287, p < 0.05) and L-Dopa duration of administration (r = −0.316, p < 0.05). L-Dopa daily dose correlated with the amplitudes of sensory nerve action potentials of the superficial peroneal and radial nerves (r = −0.312, p < 0.05) (r = −0.336, p < 0.05), respectively. (4) Conclusions: PNP is more frequent in L-Dopa-treated patients than in L-Dopa-naïve patients. The results imply that longer exposure to high doses of L-Dopa may cause vitamin B12 and folate imbalance and PNP, secondarily.