An investigation into central nervous system involvement in distal symmetrical diabetic neuropathy in type 1 diabetes mellitus.

Diabetes is a leading cause of peripheral neuropathy. It is the main initiating factor for foot ulceration and amputation resulting in considerable morbidity and remarkable consumption of scarce medical resources. Relatively little is known about the pathophysiology underlying DPN. Research into DPN has focused mainly on the peripheral nervous system (PNS) with central nervous system (CNS) involvement relatively overlooked. The studies undertaken have been designed to investigate CNS involvement in DPN. 1. Before embarking on spinal cord studies, I reviewed and modified the techniques employed in the pilot study to improve the precision and accuracy of cord cross sectional area measurements. These modifications were patiented to quality control studies, which are reported in Chapter 2. 2. I performed in-vivo cross-sectional magnetic resonance imaging of the cervical spine and reported evidence of spinal cord shrinkage (atrophy) in Painless DPN (Chapter 3). This study showed spinal cord atrophy to be an early phenomenon, present even in subclinical DPN. As the spinal cord is the caudal portion of the CNS, its involvement made us question whether the brain too may be involved. 3. Using MR spectroscopy I examined thalamic involvement in Painless DPN (Chapter 4). This deep brain nucleus is considered the gateway to all somatosensory information entering the brain, and responsible for modulation of sensory information prior to presentation to the cerebral cortex. I demonstrated thalamic biochemical abnormalities consistent with possible neuronal dysfunction in patients with Painless DPN. 4. The demonstration of thalamic neuronal dysfunction in DPN suggests that CNS involvement is not limited to the spinal cord but other important areas, responsible for somatosensory perception, may also be involved. Although the pathogenesis of thalamic involvement is unknown, it is likely that both vascular and metabolic factors that have been implicated in the pathogenesis of DPN are involved. In Chapter 4, I examined the possible role of metabolic factors in the pathogenesis of thalamic neuronal dysfunction in DPN. Using MR spectroscopy, I demonstrated a significant elevation in thalamic glutamine/glutamate in patients with diabetes. Glutamate is the most abundant excitatory neurotransmitter and implicated in various models of neuronal cell death. Astrocytes, which play an important role in glutamate/glutamine metabolism, were impaired in the thalamus of diabetic patients in this study. The combination of elevated glutamate and impaired thalamic astrocytes may provide a pathophysiological explanation for thalamic dysfunction in DPN. 5. In Chapter 5, an alternative hypothesis for thalamic neuronal dysfunction in DPN was tested. Using dynamic contrast enhanced MR perfusion imaging, I demonstrated that Painful DPN is associated with unique thalamic perfusion abnormalities. Intriguingly, these abnormalities were present in patients with Painful but not Painless DPN. 6. Finally, in Chapter 6, I conducted a randomised, double blind and placebo-control trial (RCT) comparing the efficacy and tolerability of sativex, a cannabis based medicinal extract (CBME), with placebo in the symptomatic treatment of painful DPN. This is the first ever RCT using a CBME in painful DPN. We report no significant difference in the primary outcome measure due to a massive placebo effect and that depression is a potential major confounder in such clinical trials

Microvascular Perfusion Abnormalities of the Thalamus in Painful but Not Painless Diabetic Polyneuropathy: A clue to the pathogenesis of pain in type 1 diabetes

OBJECTIVE The pathogenesis of painful diabetic neuropathy (DN) remains undetermined, with both central and peripheral mechanisms implicated. This study investigates whether thalamic perfusion abnormalities occur in painful DN. RESEARCH DESIGN AND METHODS Eighteen subjects with type 1 diabetes (no DN = 6, painful DN = 5, painless DN = 7) and six healthy volunteers (HV) were recruited. Microvascular perfusion characteristics (relative cerebral blood volume [rCBV], flow [rCBF], and transit time [ttFM]) of the thalamus and caudate nucleus were assessed using magnetic resonance perfusion imaging. The caudate nucleus was chosen to serve as an in vivo control region. RESULTS Subjects with painful DN had significantly greater thalamic rCBV (means [SD]; painful DN, 228.7 [19.5]; no DN, 202.3 [25.8]; painless DN, 216.5 [65.5]; HV, 181.9 [51.7]; P = 0.04) and the longest ttFM(s) (painful DN, 38.4 [3.6]; no DN, 35.3 [13.2]; painless DN, 35.9 [13.7]; HV, 33.7 [14.9]; P = 0.07). There was no significant difference in markers of caudate nucleus perfusion. CONCLUSIONS Painful DN is associated with increased thalamic vascularity. This may provide an important clue to the pathogenesis of pain in DN

Painful Diabetic Neuropathy Is Associated With Greater Autonomic Dysfunction Than Painless Diabetic Neuropathy

Objective: Although a clear link between diabetic peripheral neuropathy (DPN) and autonomic neuropathy is recognized, the relationship of autonomic neuropathy with subtypes of DPN is less clear. This study aimed to investigate the relationship of autonomic neuropathy with painless and painful DPN. Research design and methods: Eighty subjects (20 healthy volunteers, 20 with no DPN, 20 with painful DPN, 20 with painless DPN) underwent detailed neurophysiological investigations (including conventional autonomic function tests [AFTs]) and spectral analysis of short-term heart rate variability (HRV), which assesses sympathovagal modulation of the heart rate. Various frequency-domain (including low frequency [LF], high frequency [HF], and total power [TP]) and time-domain (standard deviation of all normal-to-normal R-R intervals [SDNN] and root mean square of successive differences [RMSSD]) parameters were assessed. Results: HRV analysis revealed significant differences across the groups in LF, HF, TP, SDNN, and RMSSD (ANOVA P < 0.001). Subgroup analysis showed that compared with painless DPN, painful DPN had significantly lower HF (3.59 ± 1.08 [means ± SD] vs. 2.67 ± 1.56), TP (5.73 ± 1.28 vs. 4.79 ± 1.51), and SDNN (2.91 ± 0.65 vs. 1.62 ± 3.5), P < 0.05. No significant differences were seen between painless DPN and painful DPN using an AFT. Conclusions: This study shows that painful DPN is associated with significantly greater autonomic dysfunction than painless DPN. These changes are only detected using spectral analysis of HRV (a simple test based on a 5-min electrocardiogram recording), suggesting that it is a more sensitive tool to detect autonomic dysfunction, which is still under-detected in people with diabetes. The greater autonomic dysfunction seen in painful DPN may reflect more predominant small fiber involvement and adds to the growing evidence of its role in the pathophysiology of painful DPN

Preservation of thalamic neuronal function may be a prerequisite for pain perception in diabetic neuropathy: A magnetic resonance spectroscopy study

IntroductionIn this study, we used proton Magnetic Resonance Spectroscopy (1H-MRS) to determine the neuronal function in the thalamus and primary somatosensory (S1) cortex in different subgroups of DPN, including subclinical- and painful-DPN.MethodOne-hundred and ten people with type 1 diabetes [20 without DPN (no-DPN); 30 with subclinical-DPN; 30 with painful-DPN; and 30 with painless-DPN] and 20 healthy volunteers, all of whom were right-handed men, were recruited and underwent detailed clinical and neurophysiological assessments. Participants underwent Magnetic Resonance Imaging at 1.5 Tesla with two 1H-MRS spectra obtained from 8 ml cubic volume voxels: one placed within left thalamus to encompass the ventro-posterior lateral sub-nucleus and another within the S1 cortex.ResultsIn the thalamus, participants with painless-DPN had a significantly lower NAA:Cr ratio [1.55 + 0.22 (mean ± SD)] compared to all other groups [HV (1.80 ± 0.23), no-DPN (1.85 ± 0.20), sub-clinical DPN (1.79 ± 0.23), painful-DPN (1.75 ± 0.19), ANOVA p &lt; 0.001]. There were no significant group differences in S1 cortical neurometabolites.ConclusionIn this largest cerebral MRS study in DPN, thalamic neuronal dysfunction was found in advanced painless-DPN with preservation of function in subclinical- and painful-DPN. Furthermore, there was a preservation of neuronal function within the S1 cortex in all subgroups of DPN. Therefore, there may be a proximo-distal gradient to central nervous system alterations in painless-DPN, with thalamic neuronal dysfunction occurring only in established DPN. Moreover, these results further highlight the manifestation of cerebral alterations between painful- and painless-DPN whereby preservation of thalamic function may be a prerequisite for neuropathic pain in DPN

Optimal pharmacotherapy pathway in adults with diabetic peripheral neuropathic pain: the OPTION-DM RCT

Background: The mainstay of treatment for diabetic peripheral neuropathic pain is pharmacotherapy, but the current National Institute for Health and Care Excellence guideline is not based on robust evidence, as the treatments and their combinations have not been directly compared. Objectives: To determine the most clinically beneficial, cost-effective and tolerated treatment pathway for diabetic peripheral neuropathic pain. Design: A randomised crossover trial with health economic analysis. Setting: Twenty-one secondary care centres in the UK. Participants: Adults with diabetic peripheral neuropathic pain with a 7-day average self-rated pain score of ≥ 4 points (Numeric Rating Scale 0–10). Interventions: Participants were randomised to three commonly used treatment pathways: (1) amitriptyline supplemented with pregabalin, (2) duloxetine supplemented with pregabalin and (3) pregabalin supplemented with amitriptyline. Participants and research teams were blinded to treatment allocation, using overencapsulated capsules and matching placebos. Site pharmacists were unblinded. Outcomes: The primary outcome was the difference in 7-day average 24-hour Numeric Rating Scale score between pathways, measured during the final week of each pathway. Secondary end points included 7-day average daily Numeric Rating Scale pain score at week 6 between monotherapies, quality of life (Short Form questionnaire-36 items), Hospital Anxiety and Depression Scale score, the proportion of patients achieving 30% and 50% pain reduction, Brief Pain Inventory – Modified Short Form items scores, Insomnia Severity Index score, Neuropathic Pain Symptom Inventory score, tolerability (scale 0–10), Patient Global Impression of Change score at week 16 and patients’ preferred treatment pathway at week 50. Adverse events and serious adverse events were recorded. A withintrial cost–utility analysis was carried out to compare treatment pathways using incremental costs per quality-adjusted life-years from an NHS and social care perspective. Results: A total of 140 participants were randomised from 13 UK centres, 130 of whom were included in the analyses. Pain score at week 16 was similar between the arms, with a mean difference of –0.1 points (98.3% confidence interval –0.5 to 0.3 points) for duloxetine supplemented with pregabalin compared with amitriptyline supplemented with pregabalin, a mean difference of –0.1 points (98.3% confidence interval –0.5 to 0.3 points) for pregabalin supplemented with amitriptyline compared with amitriptyline supplemented with pregabalin and a mean difference of 0.0 points (98.3% confidence interval –0.4 to 0.4 points) for pregabalin supplemented with amitriptyline compared with duloxetine supplemented with pregabalin. Results for tolerability, discontinuation and quality of life were similar. The adverse events were predictable for each drug. Combination therapy (weeks 6–16) was associated with a further reduction in Numeric Rating Scale pain score (mean 1.0 points, 98.3% confidence interval 0.6 to 1.3 points) compared with those who remained on monotherapy (mean 0.2 points, 98.3% confidence interval –0.1 to 0.5 points). The pregabalin supplemented with amitriptyline pathway had the fewest monotherapy discontinuations due to treatment-emergent adverse events and was most commonly preferred (most commonly preferred by participants: amitriptyline supplemented with pregabalin, 24%; duloxetine supplemented with pregabalin, 33%; pregabalin supplemented with amitriptyline, 43%; p = 0.26). No single pathway was superior in cost-effectiveness. The incremental gains in quality-adjusted life-years were small for each pathway comparison [amitriptyline supplemented with pregabalin compared with duloxetine supplemented with pregabalin –0.002 (95% confidence interval –0.011 to 0.007) quality-adjusted life-years, amitriptyline supplemented with pregabalin compared with pregabalin supplemented with amitriptyline –0.006 (95% confidence interval –0.002 to 0.014) qualityadjusted life-years and duloxetine supplemented with pregabalin compared with pregabalin supplemented with amitriptyline 0.007 (95% confidence interval 0.0002 to 0.015) quality-adjusted life-years] and incremental costs over 16 weeks were similar [amitriptyline supplemented with pregabalin compared with duloxetine supplemented with pregabalin −£113 (95% confidence interval −£381 to £90), ABSTRACT NIHR Journals Library www.journalslibrary.nihr.ac.uk viii amitriptyline supplemented with pregabalin compared with pregabalin supplemented with amitriptyline £155 (95% confidence interval −£37 to £625) and duloxetine supplemented with pregabalin compared with pregabalin supplemented with amitriptyline £141 (95% confidence interval −£13 to £398)]. Limitations: Although there was no placebo arm, there is strong evidence for the use of each study medication from randomised placebo-controlled trials. The addition of a placebo arm would have increased the duration of this already long and demanding trial and it was not felt to be ethically justifiable. Future work: Future research should explore (1) variations in diabetic peripheral neuropathic pain management at the practice level, (2) how OPTION-DM (Optimal Pathway for TreatIng neurOpathic paiN in Diabetes Mellitus) trial findings can be best implemented, (3) why some patients respond to a particular drug and others do not and (4) what options there are for further treatments for those patients on combination treatment with inadequate pain relief. Conclusions: The three treatment pathways appear to give comparable patient outcomes at similar costs, suggesting that the optimal treatment may depend on patients’ preference in terms of side effects. Trial registration: The trial is registered as ISRCTN17545443 and EudraCT 2016-003146-89. Funding: This project was funded by the National Institute for Health and Care Research (NIHR) Health Technology Assessment programme, and will be published in full in Health Technology Assessment; Vol. 26, No. 39. See the NIHR Journals Library website for further project information

SUDOSCAN: A Simple, Rapid, and Objective Method with Potential for Screening for Diabetic Peripheral Neuropathy.

Clinical methods of detecting diabetic peripheral neuropathy (DPN) are not objective and reproducible. We therefore evaluated if SUDOSCAN, a new method developed to provide a quick, non-invasive and quantitative assessment of sudomotor function can reliably screen for DPN. 70 subjects (45 with type 1 diabetes and 25 healthy volunteers [HV]) underwent detailed assessments including clinical, neurophysiological and 5 standard cardiovascular reflex tests (CARTs). Using the American Academy of Neurology criteria subjects were classified into DPN and No-DPN groups. Based on CARTs subjects were also divided into CAN, subclinical-CAN and no-CAN. Sudomotor function was assessed with measurement of hand and foot Electrochemical Skin Conductance (ESC) and calculation of the CAN risk score. Foot ESC (μS) was significantly lower in subjects with DPN [n = 24; 53.5(25.1)] compared to the No-DPN [77.0(7.9)] and HV [77.1(14.3)] groups (ANCOVA p<0.001). Sensitivity and specificity of foot ESC for classifying DPN were 87.5% and 76.2%, respectively. The area under the ROC curve (AUC) was 0.85. Subjects with CAN had significantly lower foot [55.0(28.2)] and hand [53.5(19.6)] ESC compared to No-CAN [foot ESC, 72.1(12.2); hand ESC 64.9(14.4)] and HV groups (ANCOVA p<0.001 and 0.001, respectively). ROC analysis of CAN risk score to correctly classify CAN revealed a sensitivity of 65.0% and specificity of 80.0%. AUC was 0.75. Both foot and hand ESC demonstrated strong correlation with individual parameters and composite scores of nerve conduction and CAN. SUDOSCAN, a non-invasive and quick test, could be used as an objective screening test for DPN in busy diabetic clinics, insuring adherence to current recommendation of annual assessments for all diabetic patients that remains unfulfilled

Multicentre, double-blind, crossover trial to identify the Optimal Pathway for TreatIng neurOpathic paiN in Diabetes Mellitus (OPTION-DM): study protocol for a randomised controlled trial

BACKGROUND: The number of people with diabetes is growing rapidly. Diabetes can cause nerve damage leading to severe pain in the feet, legs and hands, which is known as diabetic peripheral neuropathic pain (DPNP). In the UK, the National Institute for Health and Care Excellence (NICE) recommends amitriptyline, duloxetine, pregabalin or gabapentin as initial treatment for DPNP. If this is not effective, adding one of the other drugs in combination with the first is recommended. NICE points out that these recommendations are not based on robust evidence. The OPTION-DM randomised controlled trial has been designed to address this evidence deficit, with the aims of determining the most clinically beneficial, cost-effective and tolerated treatment pathway for patients with DPNP. METHODS/DESIGN: A multicentre, double-blind, centre-stratified, multi-period crossover study with equal allocation to sequences (1:1:1:1:1:1) of treatment pathways. Three hundred and ninety-two participants will be recruited from secondary care DPNP centres in the UK. There are three treatment pathways: amitriptyline supplemented with pregabalin, pregabalin supplemented with amitriptyline and duloxetine supplemented with pregabalin. All participants will receive all three pathways and randomisation will determine the order in which they are received. The primary outcome is the difference between 7-day average 24-h pain scores on an 11-point NRS scale measured during the final follow-up week of the treatment pathway. Secondary outcomes for efficacy, cost-effectiveness, safety, patient-perceived tolerability and subgroup analysis will be measured at week 6 and week 16 of each pathway. DISCUSSION: The study includes direct comparisons of the mainstay treatment for DPNP. This novel study is designed to examine treatment pathways and capture clinically relevant outcomes which will make the results generalisable to current clinical practice. The study will also provide information on health economic outcomes and will include a subgroup study to provide information on whether patient phenotypes predict response to treatment. TRIAL REGISTRATION: ISRCTN17545443 . Registered on 12 September 2016