Hypoglycaemia causes degeneration of large myelinated nerve fibres in the vagus nerve of insulin-treated diabetic BB/Wor rats

Exploring the impact of type II diabetes mellitus on voice quality

PURPOSE

This cross-sectional study aimed to investigate the potential of voice analysis as a prescreening tool for type II diabetes mellitus (T2DM) by examining the differences in voice recordings between non-diabetic and T2DM participants.

METHODS

60 participants diagnosed as non-diabetic (n = 30) or T2DM (n = 30) were recruited on the basis of specific inclusion and exclusion criteria in Iran between February 2020 and September 2023. Participants were matched according to their year of birth and then placed into six age categories. Using the WhatsApp application, participants recorded the translated versions of speech elicitation tasks. Seven acoustic features [fundamental frequency, jitter, shimmer, harmonic-to-noise ratio (HNR), cepstral peak prominence (CPP), voice onset time (VOT), and formant (F1-F2)] were extracted from each recording and analyzed using Praat software. Data was analyzed with Kolmogorov-Smirnov, two-way ANOVA, post hoc Tukey, binary logistic regression, and student t tests.

RESULTS

The comparison between groups showed significant differences in fundamental frequency, jitter, shimmer, CPP, and HNR (p < 0.05), while there were no significant differences in formant and VOT (p > 0.05). Binary logistic regression showed that shimmer was the most significant predictor of the disease group. There was also a significant difference between diabetes status and age, in the case of CPP.

CONCLUSIONS

Participants with type II diabetes exhibited significant vocal variations compared to non-diabetic controls.

Effect of Diabetes Mellitus Type 2 on Voice: A Systematic Review and Meta-Analysis

INTRODUCTION

Diabetes mellitus type 2 is a growing health concern that affects several systems in the body, among which is the phonatory apparatus. Voice may be affected in view of the high prevalence of myopathy and neuropathy in diseased subjects. The authors aimed to answer the following question: does type 2 diabetes have an effect on voice?

METHODS

The systematic review included search terms such as "speech, voice, larynx, glucose, diabetes, and hyperglycemia." The search strategy yielded 221 articles, only five of which satisfied the inclusion criteria. Articles were considered for inclusion using the PRISMA method. Analysis included 321 patients with type 2 diabetes mellitus and 171 controls. All studies included were case-control studies except for one study which was an observational cohort. Six parameters were chosen as endpoints for the systematic review and meta-analysis: the presence/absence of voice complaints, fundamental frequency, jitter, shimmer, noise-to-harmonic ratio, and maximum phonation time.

RESULTS

There was no significant difference in the prevalence of voice complaints (i.e., hoarseness) between diabetic patients and control groups. There was also no significant difference in any of the acoustic and aerodynamic measures between patients with type 2 diabetes and controls. These findings can be ascribed to the high resilience of the laryngeal muscles to the adverse effect of systemic diseases.

CONCLUSION

There is no consensus in the literature that the prevalence of voice symptoms in diabetic patients is significantly higher than that reported in healthy subjects.

Continuous glucose monitoring reveals a novel association between duration and severity of hypoglycemia, and small nerve fiber injury in patients with diabetes

Objective

Continuous glucose monitoring (CGM) has revealed that glycemic variability and low time in range are associated with albuminuria and retinopathy. We have investigated the relationship between glucose metrics derived from CGM and a highly sensitive measure of neuropathy using corneal confocal microscopy in participants with type 1 and type 2 diabetes.

Methods

A total of 40 participants with diabetes and 28 healthy controls underwent quantification of corneal nerve fiber density (CNFD), corneal nerve branch density (CNBD), corneal nerve fiber length (CNFL) and inferior whorl length (IWL) and those with diabetes underwent CGM for four consecutive days.

Results

CNBD was significantly lower in patients with high glycemic variability (GV) compared to low GV (median (range) (25.0 (19.0-37.5) vs 38.6 (29.2-46.9); P = 0.007); in patients who spent >4% compared to <4% time in level 1 hypoglycemia (54-69 mg/dL) (25.0 (22.9-37.5) vs 37.5 (29.2-46.9); P = 0.045) and in patients who spent >1% compared to <1% time in level 2 hypoglycemia (<54 mg/dL) (25.0 (19.8-41.7) vs 35.4 (28.1-44.8); P = 0.04). Duration in level 1 hypoglycemia correlated with CNBD (r = -0.342, P = 0.031). Duration in level 1 (181-250 mg/dL) and level 2 (>250 mg/dL) hyperglycemia did not correlate with CNFD (P > 0.05), CNBD (P > 0.05), CNFL (P > 0.05) or IWL (P > 0.05).

Conclusions

Greater GV and duration in hypoglycemia, rather than hyperglycemia, are associated with nerve fiber loss in diabetes.

Disease related changes in vocal parameters of patients with type 2 diabetes mellitus

BACKGROUND

As the duration of diabetes progresses, various disease related complications might occur in patients. The main goal of this paper is to compare acoustic and aerodynamic measures of patients with type 2 diabetes mellitus (T2DM) with a control group of healthy subjects.

METHODS

A total of 91 subjects, 51 individuals with type 2 diabetes mellitus (DM group) and 40 healthy volunteers (HV group) were participated in the study. Maximum phonation time (MPT) was captured for assessing phonatory mechanics. Acoustic voice parameters, including mean fundamental frequency (mean fo), jitter local (Jlocal), jitter absolute (Jabs), shimmer local (Slocal), shimmer decibel (SdB), and harmonics to noise ratio (HNR) were detected using the Praat software program.

RESULTS

Only for Jabs, statically significant difference was found between the groups. There were no statically significant differences between any voice parameters of HV versus those with the duration of diabetes ≥10 years and the HbA1c level ≥7%. However, statically significant differences for MPT and Slocal were found between patients with neuropathy versus HV. In addition, a comparison between patients with voice complaint versus HV showed significant differences for Slocal and SdB.

CONCLUSIONS

The findings of the present study do not provide strong evidence about the possible effect of DM on the human voice. However, diabetic neuropathy is considered to be a factor affecting the voice parameters in the target population. The physicians should pay attention to the acoustic and aerodynamic voice parameters in patients with diabetes, particularly in those with neuropathy or voice complaints.

Instrumental Acoustic Voice Characteristics in Adults with Type 2 Diabetes

OBJECTIVE

The objective of this study was to investigate if there are differences in acoustic parameters between diabetic patients and normal controls.

METHODS

A prospective cross-sectional study was performed in 83 diabetic patients and 70 healthy controls. Voice parameters including fundamental frequency (F0), jitter, shimmer, amplitude perturbation quotient, noise-to-harmonic ratio, smoothed amplitude perturbation quotient, and relative average perturbation were analyzed using Computerized Speech Lab with the Multi-Dimensional Voice Program.

RESULTS

F0 in female diabetic patients was significantly lower than controls (222.23 ± 27.89 Hz versus 241.08 ± 28.21 Hz, P< 0.01). In female diabetic subgroups with disease duration more than 10 years, poor glycemic control, or neuropathy, the F0 was still significantly lower. Multivariate analysis showed that F0 was significantly associated with diabetes after controlled for age, body mass index, presence of hypertension, and dyslipidemia. (P= 0.022). However, F0 was not able to predict the presence of diabetes as shown by logistic regression analysis (P= 0.243).

CONCLUSIONS

Voice fundamental frequency is lower in females with diabetes. However, voice fundamental frequency cannot adequately predict the presence of diabetes.

Diabetes in the practice of otolaryngology

Diabetes mellitus is the most common endocrine disease, characterized by chronic hyperglycemia. The hyperglycemic milieu leads to endothelial injury in blood vessels of variant size, which results in microangiopathy and macroangiopathy (atherosclerosis). Consequential ischemia of nerves and hyperglycemia by itself lead to nerve degeneration and generalized neuropathy, affecting most often the sensory peripheral nerves and the autonomic nervous system. Auditory, vestibular and olfactory sensorium may be compromised by DM. People with DM have an increased susceptibility to infection, as a result of neutrophil dysfunction and impaired humoral immunity. Therefore DM predisposes to certain infectious diseases, such as fungal sinusitis or malignant otitis externa, which are rare in general population. Recovery from infections or from injuries may be compromised by coexisting DM. In this review we discuss complications of DM in the head and neck region. Otolaryngologists and general practitioners should be alert to specific conditions related to DM and be minded of the relevant complications and consequences.

Acute Hypoglycemia Induces Painful Neuropathy and the Treatment of Coenzyme Q10

Diabetic neuropathic pain is reduced with tight glycemic control. However, strict control increases the risk of hypoglycemic episodes, which are themselves linked to painful neuropathy. This study explored the effects of hypoglycemia-related painful neuropathy. Pretreatment with coenzyme Q10 (CoQ10) was performed to explore the preventive effect of CoQ10 on hypoglycemia-related acute neuropathic pain. Two strains of mice were used and 1 unit/kg of insulin was given to induce hypoglycemia. Mechanical sensitivity of hindpaw withdrawal thresholds was measured using von Frey filaments. Blood glucose levels were clamped at normal levels by joint insulin and glucose injection to test whether insulin itself induced hypersensitivity. Results suggest that the increased mechanical sensitivity after insulin injection is related to decreased blood glucose levels. When blood glucose levels remained at a normal level by the linked administration of insulin and glucose, mice demonstrated no significant change in mechanical sensitivity. Pretreatment with CoQ10 prevented neuropathic pain and the expression of the stress factor c-Fos. These results support the concept that pain in the diabetic scenario can be the result of hypoglycemia and not insulin itself. Additionally, pretreatment with CoQ10 may be a potent preventive method for the development of neuropathic pain.

Histopathological nerve and skeletal muscle changes in rats subjected to persistent insulin-induced hypoglycemia

New insulin analogues with a longer duration of action and a flatter pharmacodynamic profile are developed to improve convenience and safety for diabetic patients. During the nonclinical development of such analogues, safety studies must be conducted in nondiabetic rats, which consequently are rendered chronically hypoglycemic. A rat comparator model using human insulin would be valuable, as it would enable differentiation between effects related to either persistent insulin-induced hypoglycemia (IIH) or a new analogue per se. Such a model could alleviate the need for an in-study-comparator and thereby reduce the number of animals used during development. Thus, the aims of the present study were i) to develop a preclinical animal model of persistent hypoglycemia in rats using human insulin infusion for four weeks and ii) to investigate histopathological changes in sciatic nerves and quadriceps femoris muscle tissue, as little is known about the response to persistent hypoglycemia in these tissues. Histopathologic changes in insulin-infused animals included axonal degeneration and myofibre degeneration. To our knowledge, this is the first study to show that persistent IIH provokes peripheral nerve and skeletal myofiber degeneration within the same animals. This suggests that the model can serve as a nonclinical comparator model during development of long-acting insulin analogues.

Autophagy in the posterior interosseous nerve of patients with type 1 and type 2 diabetes mellitus: an ultrastructural study

AIMS/HYPOTHESIS

We addressed the question of whether the autophagy pathway occurs in human peripheral nerves and whether this pathway is associated with peripheral neuropathy in diabetes mellitus.

METHODS

By using electron microscopy, we evaluated the presence of autophagy-related structures and neuropathy in the posterior interosseous nerve of patients who had undergone carpal tunnel release and had type 1 or type 2 diabetes mellitus, and in patients with no diabetes (controls).

RESULTS

Autophagy-related ultrastructures were observed in the samples taken from all patients of the three groups. The number of autophagy-associated structures was significantly higher (p < 0.05) in the nerves of patients with type 1 than type 2 diabetes. Qualitative and quantitative evaluations of fascicle area, diameter of myelinated and unmyelinated nerve fibres, the density of myelinated and unmyelinated fibres and the g-ratio of myelinated fibres were performed. We found degeneration and regeneration of a few myelinated axons in controls, and a well-developed neuropathy with the loss of large myelinated axons and the presence of many small ones in patients with diabetes. The pathology in type 1 diabetes was more extensive than in type 2 diabetes.

CONCLUSIONS/INTERPRETATION

The results of this study show that the human peripheral nerves have access to the autophagy machinery, and this pathway may be regulated differently in type 1 and type 2 diabetes; insulin, presence of extensive neuropathy, and/or other factors such as duration of diabetes and HbA1c level may underlie this differential regulation.

Electrophysiological characterization of spinal neurons in different models of diabetes type 1- and type 2-induced neuropathy in rats

Diabetic polyneuropathy (DPN) is a devastating complication of diabetes. The underlying pathogenesis of DPN is still elusive and an effective treatment devoid of side effects presents a challenge. There is evidence that in type-1 and -2 diabetes, metabolic and morphological changes lead to peripheral nerve damage and altered central nociceptive transmission, which may contribute to neuropathic pain symptoms. We characterized the electrophysiological response properties of spinal wide dynamic range (WDR) neurons in three diabetic models. The streptozotocin (STZ) model was used as a drug-induced model of type-1 diabetes, and the BioBreeding/Worcester (BB/Wor) and Zucker diabetic fatty (ZDF) rat models were used for genetic DPN models. Data were compared to the respective control group (BB/Wor diabetic-resistant, Zucker lean (ZL) and saline-injected Wistar rat). Response properties of WDR neurons to mechanical stimulation and spontaneous activity were assessed. We found abnormal response properties of spinal WDR neurons in all diabetic rats but not controls. Profound differences between models were observed. In BB/Wor diabetic rats evoked responses were increased, while in ZDF rats spontaneous activity was increased and in STZ rats mainly after discharges were increased. The abnormal response properties of neurons might indicate differential pathological, diabetes-induced, changes in spinal neuronal transmission. This study shows for the first time that specific electrophysiological response properties are characteristic for certain models of DPN and that these might reflect the diverse and complex symptomatology of DPN in the clinic.

Effect of insulin-induced hypoglycaemia on the peripheral nervous system: focus on adaptive mechanisms, pathogenesis and histopathological changes

Insulin-induced hypoglycaemia (IIH) is a common acute side effect in type 1 and type 2 diabetic patients, especially during intensive insulin therapy. The peripheral nervous system (PNS) depends on glucose as its primary energy source during normoglycaemia and, consequently, it may be particularly susceptible to IIH damage. Possible mechanisms for adaption of the PNS to IIH include increased glucose uptake, utilisation of alternative energy substrates and the use of Schwann cell glycogen as a local glucose reserve. However, these potential adaptive mechanisms become insufficient when the hypoglycaemic state exceeds a certain level of severity and duration, resulting in a sensory-motor neuropathy with associated skeletal muscle atrophy. Large myelinated motor fibres appear to be particularly vulnerable. Thus, although the PNS is not an obligate glucose consumer, as is the brain, it appears to be more prone to IIH than the central nervous system when hypoglycaemia is not severe (blood glucose level ≤ 2 mm), possibly reflecting a preferential protection of the brain during periods of inadequate glucose availability. With a primary focus on evidence from experimental animal studies investigating nondiabetic IIH, the present review discusses the effect of IIH on the PNS with a focus on adaptive mechanisms, pathogenesis and histological changes.

Laryngeal sensory neuropathy in patients with diabetes mellitus

OBJECTIVE

To determine the prevalence of laryngeal sensory neuropathy in patients with type 2 diabetes mellitus.

METHODS

A cross-sectional study was performed, comprising 50 patients diagnosed with type 2 diabetes mellitus and 36 healthy controls. In the diabetic group, glycaemic control level, disease duration and presence of neuropathy were assessed. Participants were diagnosed with laryngeal sensory neuropathy if they had a cough, globus pharyngeus or throat clearing lasting for more than six weeks, in the absence of laryngopharyngeal reflux disease, allergies, asthma, angiotensin-converting enzyme inhibitor intake or psychogenic disorders.

RESULTS

In the diabetic group, the mean age ± standard deviation was 44.66 ± 10.07 years. Sixty per cent of patients were male, 42 per cent had had diabetes for more than five years and 52 per cent had average to poor glycaemic control. The prevalence of laryngeal sensory neuropathy was 42 per cent in the diabetic group, compared with 13.9 per cent in controls; this difference was statistically significant (p = 0.005). There was no association between the prevalence of laryngeal sensory neuropathy and glycaemic control level, disease duration or presence of neuropathy.

CONCLUSION

Laryngeal sensory neuropathy is more common in patients with type 2 diabetes mellitus than in controls.

Neurologic damage in hypoglycemia

Hypoglycemia occurs in diabetic patients as a consequence of treatment with hypoglycemic agents, in insulinoma patients as a result of excessive insulin production, and in infants as a result of abnormal regulation of metabolism. Profound hypoglycemia can cause structural and functional disturbances in both the central (CNS) and the peripheral nervous system (PNS). The brain is damaged by a short and severe episode of hypoglycemia, whereas PNS pathology appears after a mild and prolonged episode. In the CNS, damaged mitochondria, elevated intracellular Ca2(+) level, released cytochrome c to the cytosol, extensive production of superoxide, increased caspase-3 activity, release of aspartate and glutamate from presynaptic terminals, and altered biosynthetic machinery can lead to neuronal cell death in the brain. Considering the PNS, chronic hypoglycemia is associated with delayed motor and sensory conduction velocities in peripheral nerves. With respect to pathology, hypoglycemic neuropathy in the PNS is characterized by Wallerian-like axonal degeneration that starts at the nerve terminal and progresses to a more proximal part of the axon, and motor axons to the muscles may be more severely damaged than sensory axons. Since excitatory neurotransmitters primarily involve the neuron in the CNS, this "dying back" pattern of axonal damage in the PNS may involve mechanisms other than excitotoxicity.

Goiter and laryngeal sensory neuropathy

Objective. Examining the prevalence of laryngeal sensory neuropathy (LSN) in goiter patients versus a control group. Study Design. Cross-sectional study. Methods. 33 Goiter patients were enrolled versus 25 age-matched controls. TSH levels, size of thyroid gland, and presence or absence of thyroid nodules were reported. Subjects were asked about the presence or absence of any of the following symptoms: cough, globus pharyngeus, and/or throat clearing that persistented for more than 6 weeks. The presence of one or more of these symptoms for at least six weeks in the absence of LPRD, allergy, asthma, ACE inhibitor intake, and psychogenic disorder was defined as LSN. Results. For goitrous patients mean age (years) was (41.73 ± 9.47) versus (37.44 ± 10.89) for controls. 82% goitrous patients had known nodules and 27% carried a simultaneous diagnosis of hypothyroidism. Among those with documented size (61%), mean total thyroid volume was 26.996 ± 14.852 cm³, with a range from 9.430 to 67.022 cm³. The overall prevalence of LSN among goitrous patients was 42% versus 12% among controls (P = 0.0187). There was no correlation between LSN, size of thyroid gland, and TSH level. Conclusion. The prevalence of LSN in goitrous patients is significantly higher than that in a nongoitrous population.

Prevalence of laryngopharyngeal reflux disease in patients with diabetes mellitus

OBJECTIVE

To study the prevalence of laryngopharyngeal reflux disease (LPRD) in patients with type 2 diabetes mellitus (T2DM) and report the correlation between LPRD and glycemic control, duration of the disease, and presence of neuropathy.

MATERIALS AND METHODS

This is a cross-sectional study of 100 patients with T2DM and 33 controls matched according to age and gender. The reflux symptom index (RSI) was used to assess the presence of LPRD. A score greater than 10 was considered diagnostic of LPRD.

RESULTS

Twenty-two percent of patients with T2DM had RSI above 10 versus 9.1% of controls. The difference was not statistically different (P value of 0.100). The average score of all symptoms of LPRD was higher in the diabetic group compared with the control group. There was a significant increase in the average score of "throat clearing" and "lump sensation in throat," with a borderline significant increase in "annoying cough" in patients with diabetes versus controls (respective P values of 0.03, 0.025, and 0.066). There was no correlation between LPRD and any of the demographic variables except neuropathy.

CONCLUSION

Patients with T2DM are more likely to have LPRD compared with controls. However, the prevalence of LPRD is not significantly higher in diabetic patients compared with controls. When present, LPRD correlates with neuropathy.

LEVEL OF EVIDENCE

2c.

Vocal characteristics in patients with type 2 diabetes mellitus

The objective of this study is to report the vocal characteristics of patients with type 2 diabetes mellitus in relation to disease duration, glycemic control, and neuropathy. This is a prospective study. The setting is institutional setting. A total of 82 patients were recruited for this study, and a healthy control group matched according to age and gender was recruited. Subjects underwent acoustic analysis and perceptual evaluation using the GRABS classification where G stands for grading, R for roughness, A for asthenia, B for breathiness, and S for straining using a scale of 0–3 where o stands for normal and three for severe deviation from normal. There was no significant difference in any of the acoustic variables between diabetic patients and control. There was no significant difference in the mean score of any of the perceptual evaluation parameters between diabetic patients and control, despite the fact that the mean scores were all higher in the diseased group except for roughness. When looking at subgroups, we see that diabetic patients with poor glycemic control and with neuropathy had significantly higher mean score for the G overall grade of the voice compared to controls with P values of 0.005 and 0.009, respectively. What is also worth noting is that diabetic patients with poor glycemic control had more straining compared to controls, P value 0.043. Patients with type 2 diabetes mellitus and poor glycemic control or neuropathy have a significant difference in the grade of their voice compared to controls.

Differential neuropathies in hyperglycemic and hypoglycemic diabetic rats

We investigated the effects of hyperglycemia and hypoglycemia on development of peripheral neuropathy in somatic motor and sensory nerves in type 1 diabetic BB/Wor rats. The animals were maintained in a hyper- or hypoglycemic state by treatment with insulin for 3 months. Nondiabetic siblings served as controls. Qualitative analysis of the gastrocnemius and sural nerves by light and electron microscopy revealed signs of Wallerian-type axonal degeneration and regeneration of large myelinated fibers in the hypoglycemic but not the hyperglycemic animals. Degeneration was more common in the gastrocnemius nerve than in the sural nerve. In hypoglycemic rats, myelinated fibers in both the gastrocnemius and sural nerves had significantly shorter internodes and smaller diameters. The decreased fiber diameter was related (r = -0.9) to the duration of severe hypoglycemia (</=2.5 mmol/L). Myelinated fiber occupancy was also decreased without any significant changes in fiber counts in both the gastrocnemius and sural nerves. In hyperglycemic rats, myelinated fibers in the sural nerve but not the gastrocnemius nerve had smaller diameters compared with controls. We conclude that hypoglycemia has a more severe impact on somatic motor nerves than on somatic sensory nerves, whereas hyperglycemia affects only somatic sensory nerves.

Phenotypic characterization of gastric sensory neurons in mice

Recent studies suggest that the capsaicin receptor [transient receptor potential vanilloid (TRPV)1] may play a role in visceral mechanosensation. To address the potential role of TRPV1 in vagal sensory neurons, we developed a new in vitro technique allowing us to determine TRPV1 expression directly in physiologically characterized gastric sensory neurons. Stomach, esophagus, and intact vagus nerve up to the central terminations were carefully dissected and placed in a perfusion chamber. Intracellular recordings were made from the soma of nodose neurons during mechanical stimulation of the stomach. Physiologically characterized neurons were labeled iontophoretically with neurobiotin and processed for immunohistochemical experiments. As shown by action potential responses triggered by stimulation of the upper thoracic vagus with a suction electrode, essentially all abdominal vagal afferents in mice conduct in the C-fiber range. Mechanosensitive gastric afferents encode stimulus intensities over a wide range without apparent saturation when punctate stimuli are used. Nine of 37 mechanosensitive vagal afferents expressed TRPV1 immunoreactivity, with 8 of the TRPV1-positive cells responding to stretch. A small number of mechanosensitive gastric vagal afferents express neurofilament heavy chains and did not respond to stretch. By maintaining the structural and functional integrity of vagal afferents up to the nodose ganglion, physiological and immunohistochemical properties of mechanosensory gastric sensory neurons can be studied in vitro. Using this novel technique, we identified TRPV1 immunoreactivity in only one-fourth of gastric mechanosensitive neurons, arguing against a major role of this ion channel in sensation of mechanical stimuli under physiological conditions.