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.

Co-localization of pain and reduced intra-epidermal nerve fiber density in individuals with HIV-associated sensory neuropathy

IntroductionThere is poor correlation between decreases in intra-epidermal nerve fiber density (IENFD) and the presence of pain in HIV-associated sensory neuropathy (HIV-SN) and other painful distal symmetrical polyneuropathies.ObjectiveWe investigated whether in individuals with HIV-SN, having pain at the ankle skin biopsy site was associated with lower IENFD compared to when there was no pain at the ankle biopsy site.MethodsWe recruited 15 individuals with symptomatic HIV-SN. Nine had pain at the site where the ankle biopsy was taken, while six did not. Skin punch biopsies for IENFD quantification were taken from the ankle and the thigh. Contrasts between the two groups were made using the overlap of confidence interval (CI) method.ResultsIENFD was substantially lower in the group that had pain at the site of the ankle biopsy compared to the other group [6.6 (CI: 5.3 to 7.2) vs. 3.3 (CI: 10.0 to 15.0) fibers/mm]. However, there was no group differences at the thigh biopsy site [15.6 (CI: 15.0 to 15.9) vs 16.2 (CI: 14.5 to 17.8) fibers/mm]. When taking the ratio of ankle IENFD:thigh IENFD, the point estimate for the pain at the ankle group [0.43 (CI: 0.36 to 0.48)] was about half that of the other group [0.81 (CI: 0.68 to 0.87)].ConclusionThus, co-localization of pain to the ankle is associated with meaningful decreases in ankle IENFD.SummaryHaving pain at the ankle biopsy site is associated with lower intra-epidermal nerve fiber density compared to not having pain at the ankle biopsy site.

Case 62: Small Fiber Neuropathy with Symptomatic Improvement on Immune Globulins

Autonomic testing revealed length-dependent small fiber neuropathy affecting sensory fibers. Repeated titer of acetylcholine ganglionic antibody was negative, but repeated epidermal nerve fiber density testing showed progressive deterioration. Symptoms improved with intravenous immune globulin therapy.

Contact Heat Evoked Potentials

Somatic small-diameter fibers in the Aδ‎ and C classes are difficult to assess objectively. Beyond skin punch biopsy for epidermal nerve fiber density, which examines only a small percentage of the cutaneous nerve fibers, nociceptive evoked potentials provide a number of techniques to study these heat- and pain-mediating neural pathways. Of the available approaches, contact heat evoked potentials (CHEPS) present a number of advantages. Using robust and highly quantified discrete bursts of heat by a thermofoil electrode, safeguarded by layers of redundant internal algorithms to insure stimuli remain within strict tolerances, CHEPS evokes scalp responses typically in the 5–50 μ‎V amplitude range in normal adult subjects from Cz–TE into the eighth decade, which can be readily resolved averaging 10–14 stimuli. Having been used in individuals with a variety of peripheral and central disorders affecting spinothalamic pathways, CHEPS is a promising technique in clinical neurophysiology.