Auditory brainstem evoked potentials in insulin-dependent diabetics with and without peripheral neuropathy

Cochlear dysfunction and microvascular complications in patients with type 1 diabetes mellitus

Sensorineural hearing impairment has been associated with DM, and it is probably linked to the same pathophysiological mechanisms as well-established in microvascular diabetes complications. The study of otoacoustic emissions (OAEs) is useful to identify subclinical cochlear dysfunction. Therefore, the aim of this study was to evaluate the association between abnormal OAEs responses, diabetic kidney disease (DKD) and diabetic cardiac autonomic neuropathy (CAN). We performed a cross-sectional study with 37 type 1 DM patients without auditory symptoms, submitted to the study of Distortion Product Otoacoustic Emissions (DPOAEs) and screened for DKD and CAN. The otoacoustic emissions responses were considered abnormal in 27/37 (73%) patients. A correlation was found between abnormal OAEs responses and presence of DKD (r = 0.36, p < 0.05), and 14/16 (88%) patients with a lower amplitude of OAEs in 8 kHz frequency band presented DKD. Abnormal OAEs responses in the 6 kHz frequency band were correlated with the presence (r = 0.41, p = 0.01) and severity of CAN (r = 0.44, p < 0.001). Additionally, 7/9 (78%) patients with abnormal OAE responses in this frequency also presented abnormal CAN scores. Our results suggest that abnormal otoacoustic emissions responses in high frequency bands are associated with diabetes microvascular complications and could be a risk marker for DKD and CAN, presenting low sensitivity and high specificity. Therefore, assuming that hearing impairment is a pre-clinical stage of hearing loss, performing distortion product otoacoustic emissions in T1DM patients with microvascular complications could be useful to identify those who would be benefit with regular audiologic follow up and tighter diabetes control.

Interaction between diabetes mellitus and hypertension on hearing of elderly

INTRODUCTION

Chronic diseases and metabolic changes may act as accelerating factor in the degeneration of the auditory system due to age. However, studies involving an association between hearing loss and diabetes mellitus (DM) and hypertension (HA) in the elderly have shown controversial conclusions. Thus, further studies on this topic are needed in order to elucidate the effect of these chronic diseases on the auditory system.

AIM

To compare the hearing thresholds of elderly patients with DM, HA and DM + HA with a control group (CG).

METHODS

Retrospective study was conducted through survey charts of 80 elderly people with full hearing assessment, between 2008 and 2012. Subjects were divided into four groups: DM, HA, DM + HA and without chronic diseases known (CG). The ANOVA, Tukey and Mauchly tests, with a significance level of 0.05, were used.

RESULTS

There was no statistically significant difference between the ears, which are grouped. Comparisons between the means of hearing thresholds of CG and DM or HA showed no statistically significant differences. However, a statistically significant difference in the comparison between these three groups and DM + HA group for several of the frequencies evaluated was observed.

CONCLUSION

It was found that older adults with DM and hypertension associated showed greater hearing impairment in comparison with the other groups, suggesting a synergistic effect of the two chronic diseases on hearing.

Cardiovascular risk factors as causes for hearing impairment

The purpose of this paper is to provide a contemporary review of the correlation between cardiovascular risk factors (CVRFs) and hearing impairment (HI) . We conducted a comprehensive review of the literature in order to assess the effects of the different CVRFs on HI. We focused on the pathological findings in the inner ear and their correlation with cochlear function in population-based studies. We found that CVRFs adversely affect hearing acuity. HI diagnosis should be accompanied by detecting and treating CVRFs, according to the presented outline, which may augment hearing rehabilitation and improve the general health and the well-being of the patient. © 2014 S. Karger AG, Basel.

Type-2 diabetes mellitus and auditory brainstem response

OBJECTIVE

Diabetes mellitus (DM) causes pathophysiological changes at multiple organ system. With evoked potential techniques, the brain stem auditory response represents a simple procedure to detect both acoustic nerve and central nervous system pathway damage. The objective was to find the evidence of central neuropathy in diabetes patients by analyzing brainstem audiometry electric response obtained by auditory evoked potentials, quantify the characteristic of auditory brain response in long standing diabetes and to study the utility of auditory evoked potential in detecting the type, site, and nature of lesions.

DESIGN

A total of 25 Type-2 DM [13 (52%) males and 12 (48%) females] with duration of diabetes over 5 years and aged over 30 years. The brainstem evoked response audiometry (BERA) was performed by universal smart box manual version 2.0 at 70, 80, and 90 dB. The wave latency pattern and interpeak latencies were estimated. This was compared with 25 healthy controls (17 [68%] males and 8 [32%] females).

RESULT

In Type-2 DM, BERA study revealed that wave-III representing superior olivary complex at 80 dB had wave latency of (3.99 ± 0.24) ms P < 0.001, at 90 dB (3.92 ± 0.28) ms P < 0.001 compared with control. The latency of wave III was delayed by 0.39, 0.42, and 0.42 ms at 70, 80, and 90 dB, respectively. The absolute latency of wave V representing inferior colliculus at 70 dB (6.05 ± 0.27) ms P < 0.001, at 80 dB (5.98 ± 0.27) P < 0.001, and at 90 dB (6.02 ± 0.30) ms P < 0.002 compared with control. The latency of wave-V was delayed by 0.48, 0.47, and 0.50 ms at 70, 80, and 90 dB, respectively. Interlatencies I-III at 70 dB (2.33 ± 0.22) ms P < 0.001, at 80 dB (2.39 ± 0.26) ms P < 0.001, while at 90 dB (2.47 ± 0.25) ms P < 0.001 when compared with control. Interlatencies I-V at 70 dB (4.45 ± 0.29) ms P < 0.001 at 80 dB (4.39 ± 0.34) ms P < 0.001, and at 90 dB (4.57 ± 0.31) ms P < 0.001 compared with control. Out of 25 Type-2 DM, 13 (52%) had diabetic neuropathy, of which 12 (92%) showed abnormal BERA. In nonneuropathic [12 (48%)] only 6 (50%) showed abnormal BERA.

CONCLUSION

Delay in absolute latencies and interpeak latencies by BERA demonstrates defect at level of brainstem and midbrain in long standing Type-2 diabetes subjects, which is more pronounced in those with neuropathy.

Auditory brainstem evoked responses in insulin-dependent (ID) and non-insulin-dependent (NID) diabetic subjects with normal hearing

Hearing impairment has been reported to be one of the late complications of diabetes mellitus (DM), and the frequency varies. Previous data suggest that auditory brainstem potentials deteriorate long before the hearing impairment appears in patients with DM. Delay in neural conductance along the auditory pathway due to DM was assessed by means of auditory brainstem response (ABR) in 43 patients with normal hearing in a controlled study. Patients were classified according to age, presence of neuropathy. metabolic control, and duration and type of DM. ABR recordings revealed that absolute latencies of waves I, III and V were prolonged significantly in the diabetic group when compared to the control group (p < 0.05). When two diabetic groups (insulin-dependent and non-insulin-dependent) were compared with each other, the difference between the latency of wave I and the inter-peak latencies of I-III, III-V and I-V was not significant (p > 0.05). However, the difference between the latencies of waves III and V in the two diabetic groups was statistically significant. The duration of diabetes, blood glucose level and age were not associated with prolonged ABR latencies (p > 0.05). Prolongation of latency of ABR in patients with DM should alert us to possible damage to the auditory nerve, and close follow-up is needed in these patients.

Relationship of Type 2 diabetes to the prevalence, incidence and progression of age-related hearing loss

AIMS

Type 2 diabetes and associated microvascular abnormalities are postulated to affect hearing. Our study reports on the relationship between Type 2 diabetes and the prevalence, 5-year incidence and progression of hearing impairment in a representative, older, Australian population.

METHODS

The Blue Mountains Hearing Study is a population-based survey of age-related hearing loss conducted in a defined suburban area, west of Sydney. Hearing loss was defined as the pure-tone average of frequencies 0.5, 1.0, 2.0 and 4.0 kHz > 25 decibels hearing level (dB HL) in the better ear (bilateral hearing loss). Type 2 diabetes was defined from reported physician-diagnosed diabetes or fasting blood glucose > or = 7.0 mmol/l.

RESULTS

Age-related hearing loss was present in 50.0% of diabetic participants (n = 210) compared with 38.2% of non-diabetic participants (n = 1648), odds ratio (OR) 1.55 [95% confidence interval (CI) 1.11-2.17], after adjusting for multiple risk factors. A relationship of diabetes duration with hearing loss was also demonstrated. After 5 years, incident hearing loss occurred in 18.7% of participants with, and 18.0% of those without diabetes, adjusted OR 1.01 (CI 0.54-1.91). Progression of existing hearing loss (> 5 dB HL), however, was significantly greater in participants with newly diagnosed diabetes (69.6%) than in those without diabetes (47.8%) over this period, adjusted OR 2.71 (CI 1.07-6.86).

CONCLUSIONS

Type 2 diabetes was associated with prevalent, but not incident hearing loss in this older population. Accelerated hearing loss progression over 5 years was more than doubled in persons newly diagnosed with diabetes. These data explore further reported links between Type 2 diabetes and age-related hearing loss.

Brainstem auditory evoked potentials and middle latency auditory evoked potentials in patients with impaired glucose tolerance

AIMS

The aim was to investigate the effects of impaired glucose tolerance (IGT) on the central nervous system via brainstem auditory evoked potentials (BAEPs) and middle latency auditory evoked potentials (MLAEPs), and on the peripheral nervous system via nerve conduction studies (NCS).

METHODS

Thirty patients with IGT and 20 control subjects underwent NCS, BAEPs and MLAEPs.

RESULTS

Tibial distal motor latencies were significantly prolonged in the IGT group; no differences in other parameters, including BAEPs and MLAEPs, were observed between the IGT and control subjects.

CONCLUSION

Brainstem involvement may not be seen in IGT patients as in DM. The was no obvious electrophysiological finding indicating peripheral nervous system disfunction in our patients.

Auditory Evaluation in Patients with Type 1 Diabetes

Objectives:

We performed a prospective clinical study of the cochleovestibular symptoms and the risk cofactors and characteristics of hearing loss in patients with type 1 diabetes.

Methods:

Group 1 consisted of 40 patients with type 1 diabetes, and group 2 consisted of 20 control subjects without diabetes. All participants answered a questionnaire, and their medical records were reviewed. They also were submitted to otorhinolaryngological examinations and to auditory tests (pure tone audiometry and acoustic immitance and auditory brain stem response [ABR] tests).

Results:

Dyslipidemia, hypertension, retinopathy, and diabetic neuropathy were not frequent in the patients of group 1, but incipient nephropathy was present in 47.5% of them. The most frequent cochleovestibular symptoms were tinnitus and hearing loss. Sensorineural hearing loss was found in 4 patients of group 1 and was predominantly bilateral, symmetric, and affecting the high frequencies, coexisting with normal vocal discrimination. These patients had a longer time from diabetes diagnosis and had poor glycemia control. A delay of ABR interpeak latency I-III was observed in 11.25% of the group 1 ears. All patients of group 2 presented normal audiograms and ABR tests.

Conclusions:

In group 1, the most frequent cochleovestibular symptoms were tinnitus and hearing loss. The sensorineural hearing loss was mild, symmetric, and predominantly high-frequency. A delay of ABR interpeak latencies was detected in the patients of group 1 who had normal audiometric thresholds.

Potencial cognitivo P300 em indivíduos com diabetes mellitus

Diabetes Mellitus pode acarretar complicações nos olhos, rins, nervos cranianos, nervos periféricos, ouvidos, etc. A função cognitiva também parece estar prejudicada em indivíduos portadores de Diabetes Mellitus, visto que as estruturas corticais e subcorticais responsáveis por esta função estão prejudicadas em alguns pacientes dependentes de insulina. O potencial cognitivo P300 tem sido usado como um procedimento objetivo para avaliar a função cognitiva cerebral. OBJETIVO: Analisar a sensibilidade do potencial cognitivo P300 para detectar alterações no córtex auditivo decorrentes do Diabetes Mellitus. FORMA DE ESTUDO: coorte transversal. MATERIAL E MÉTODO: Participaram deste estudo 16 indivíduos diabéticos de ambos os sexos, com idade variando de 7 a 71 anos, e 17 indivíduos não-diabéticos equiparados quanto ao sexo, idade e limiar auditivo. Os procedimentos de avaliação foram: Audiometria Tonal Liminar (ATL) e potencial cognitivo P300. No grupo diabético foi realizada a medida do valor glicêmico antes da realização do P300. RESULTADOS: Os resultados obtidos na ATL não mostraram diferença estatisticamente significante. Foi observado diferença estatisticamente significante entre os grupos, quando analisado a latência do componente P3, medido em Fz. Houve correlação entre a glicemia e a latência e amplitude do P300. CONCLUSÃO: A pesquisa do potencial cognitivo P300 é um importante procedimento para prevenir e diagnosticar precocemente de alterações neurológicas em indivíduos com Diabetes Mellitus.

Cognitive P300 potential in subjects with diabetes mellitus

Diabetes Mellitus may lead to alterations in the eyes, kidneys, cranial nerves, peripheral nerves, ears etc. The cognitive function also seems to be compromised in subjects presented with Diabetes Mellitus, since the cortical and subcortical structures responsible for this function are hindered in some insulin-dependent patients. The cognitive potential P300 has been used as an objective procedure to assess cerebral cognitive functions.

AIM

To analyze the sensitivity of P300 cognitive potential for the detection of alterations on the auditory cortex secondary to Diabetes Mellitus.

STUDY DESIGN

transversal cohort.

MATERIAL AND METHOD

Sixteen diabetic subjects of both genders aged 7 to 71 years, and seventeen non-diabetic individuals at the same age range participated in this study. The evaluation procedures were pure tone audiometry (PTA) and P300 cognitive potential. Glycemia of the group presented with Diabetes was assessed prior to applying P300.

RESULTS

No statistically significant difference was shown for PTA results. A statically significant difference was observed between groups when analyzing the latency of P300 component measured in Fz. There was a correlation between glycemia and latency and amplitude of P300.

CONCLUSION

The investigation of the cognitive potential of P300 is an important procedure for prevention and early diagnosis of neurological changes in individuals presented with Diabetes Mellitus.

Early Identification of Hearing Impairment in Patients With Type 1 Diabetes Mellitus

OBJECTIVE

The aim of this study was to evaluate the cochlear micromechanics and central auditory function in patients with type I diabetes mellitus and to identify the site of possible dysfunction.

METHODS

Cochlear activity was evaluated by recording distortion product otoacoustic emissions (DPOAEs). DPOAEs were performed using an ILO 92 Otodynamics Analyser. Functional changes in the retrocochlear auditory pathway were evaluated by auditory brainstem responses (ABRs). DPOAEs and ABRs were measured in 42 normally hearing patients with type 1 diabetes mellitus aged 21 to 42 years, and 33 age- and sex-matched nondiabetic control subjects.

RESULTS

Both of the groups (diabetic and control) had normal and undifferentiated results in tonal and impedance audiometry. ABR peripheral transmission time (wave I) and central transmission time (interpeak latencies I-V) were significantly delayed in the diabetic compared with normal subjects, and the mean amplitudes of various DPOAEs were significantly reduced in the diabetic patients compared with the control subjects.

CONCLUSIONS

Combined use of different procedures for monitoring central and peripheral portions of the auditory pathway in diabetic patients showed alterations in cochlear micromechanics and the retrocochlear auditory pathway. Hearing impairment in diabetic patients is usually mild and subclinical, and can be detected early by accurate and objective audiometric methods.

Brain stem evoked responses in patients with diabetes mellitus

Diabetes mellitus is a systeihic disorder which targets multiple organs. The neurological involvement is not only in the form of peripheral neuropathy, but may also lead to central neuropathy. To evaluate the presence of central neuropathy auditory brain stem evoked responses were recorded from 25 normal hearing diabetic subjects aged 28 years to 49 years (Mean age 44.28 years) at 2KHz, 4KHz, & 4KHz, frequencies. The results obtained were compared with those obtained from 10 subjects with normal hearing of matched age and sex. In diabetic subjects, abnormal wave latencies were correlated with blood glucose level, duration of illness and peripheral neuropathy.The absolute latencies and inter peak latencies were significantly impaired (P<.001) in diabetic subjects as compared to control subjects at 2, 4, & 6KHz frequencies. The incidence of delayed wave latencies was 64%, 72%. & 84% at 2KHz, 4KHz, & 6KMz respectively suggesting that if brain stem evoked response audiometry is conducted at higher frequency like 6KBz in diabetic patients, the involvement of central neural axis can be detected earlier. This study is the first to demonstrate that brain stem evoked response audiometry is a useful non-invasive test for earlier detection of damage in central neural axis in patients of diabetes mellitus. There is no relationship between the delayed wave latencies and the blood glucose level, however there exists a significant relationship between the delayed wave latencies and the duration of disease & peripheral neuropathy.

Consumption of a High-Galactose Diet Induces Diabetic-Like Changes in the Inner Ear

Diabetes mellitus is a disease that affects multiple organ systems. In our laboratory it has been shown that there is a significant loss of outer hair cells in genetically diabetic rats. Galactosemia can also produce diabetic-like changes. This study was performed to demonstrate whether these changes also occur in the cochlea. Three groups of Sprague-Dawley rats were used and fed either a control diet, a 50% galactose diet, or a 50% galactose diet with the addition of an aldose reductase inhibitor. After 6 months the animals were killed, and the cochleas were removed, fixed, and stained. Diabetes-induced damage was assessed by counting the hair cells and calculating the neuroganglion cell density. The histopathologic changes induced by galactose were manifested as outer hair cell loss and a decrease in neuroganglion cell density. Control animals had the least amount of hair cell loss and the greatest neuroganglion cell density of all three groups. Galactose-only animals demonstrated the most pronounced changes in both hair cell loss and neuroganglion cell degeneration; however, only changes of neuroganglion cell density in the basal turn were significant. The addition of an aldose reductase inhibitor provided inconclusive results in both hair cell determination and neuroganglion cell density; however, generally the inhibitor partially prevented the damage produced by galactose. These results suggest that a high-galactose diet can induce diabetic-like changes in the cochlea.

Changes in auditory P300 event-related potentials and brainstem evoked potentials in diabetes mellitus

To investigate the influence of diabetes mellitus on higher cognitive functions electrophysiologically, we studied auditory P300 event-related potentials (P300) in 40 NIDDM patients, taking into account wave I-V latencies (I-V) in auditory brainstem evoked potentials, clinical parameters and head MRI findings. Compared with 20 controls, diabetics had significantly longer P300 and I-V latencies. P300 latencies in diabetics correlated with neither I-V, HbA1, blood glucose levels, nor disease duration. Of the 13 diabetics investigated neuroradiologically, four had lacunar infarcts with prolonged electrophysiological values. The remaining nine had normal MRI scans, but their physiological parameters were still significantly longer than those of controls. These findings suggest that NIDDM can independently alter higher cognitive and the central auditory pathway functions. Our data also suggest that these alterations occur regardless of the recent metabolic derangement and disease duration. Cerebrovascular ischemia, if present, also appears to contribute in part to cognitive alterations.

Improvement of metabolic control does not normalize auditory brainstem latencies in subjects with insulin-dependent diabetes mellitus

INTRODUCTION

In our previous study (Am J Otolaryngol 14:413-418, 1993), we reported that prolonged auditory brainstem response latencies are associated with microvascular complications and the duration of diabetes in patients with insulin-dependent diabetes mellitus (IDDM). To investigate whether short-term improvement in metabolic control also affects ABR-responses, we compared ABR-latencies in subjects with IDDM before and after intensified insulin and diet therapy.

MATERIALS AND METHODS

Auditory brainstem latencies were measured in 13 subjects with IDDM (mean age: 25 years) before and after intensified insulin and diet therapy. The acoustic stimulus was a half sine wave with a duration of 0.250 millisecond and a frequency of 2,000 Hz. The stimulus was presented monaurally with fixed polarity through shielded headphones TDH-39 at repetition rate of 10 Hz and at 90 dB hearing level. All subjects had normal hearing ability. Glycated hemoglobin A1C (GHbA1C), blood glucose immediately before ABR-measurements, and mean blood glucose during 24 hours before auditory studies were measured before and after intensified therapy.

RESULTS

During intensified insulin therapy, GHbA1C improved significantly (P < .05) in study subjects. However, no changes were observed in ABR-latencies. We also studied those 10 patients whose blood glucose improved during intensified insulin therapy. Although blood glucose was significantly lower (P < .01) after intensified insulin therapy compared with that at baseline, no changes were observed between ABR-latencies at baseline and follow-up.

CONCLUSION

ABR-latencies were not affected by improvement in metabolic control in patients with IDDM. Our finding suggests that delayed ABR-latencies found in patients with IDDM are not caused by poor metabolic control of diabetes but rather by other mechanisms, for example, microvascular complications.

Brainstem auditory evoked potentials during hypoglycaemia in insulin-dependent diabetic children

Brainstem auditory evoked potentials (BAEP) were studied in 10 type 1 diabetic children during normoglycaemia (5.5 +/- 0.4 mmol/l), hypoglycaemia and in the post-hypoglycaemic state. In addition, BAEP during normoglycaemia in diabetic children were compared with those of an age-, weight- and sex-matched group of healthy control children. No significant differences were observed between all latencies of the diabetic children compared with those of the healthy children during normoglycaemia. During induction of hypoglycaemia a minor (p < 0.05) prolongation of the inter-peak latency I-V at a blood glucose concentration of 4.1 +/- 0.5 mmol/l was observed. This prolongation was not aggravated at glucose nadir (1.7 +/- 0.3 mmol/l). In conclusion, and in contrast with previous findings in non-diabetic children and in adults with type 1 diabetes, no changes in BAEP were demonstrated during short-term severe hypoglycaemia in diabetic children and only minor transient changes were seen during the initial phase of a standardized induction of hypoglycaemia.

Hearing thresholds in insulin-dependent diabetic patients

Hearing thresholds were studied in 53 patients with insulin-dependent diabetes mellitus (IDDM) and 42 randomly selected non-diabetic control subjects, aged between 20 and 40 years. The hearing level tended to be worse in diabetic patients than in control subjects, but the differences were statistically significant only at frequencies of 6,000 and 8,000 Hz. Microvascular complications (retinopathy and nephropathy), and the duration of diabetes were associated with the elevated hearing thresholds. In contrast, poor metabolic control (high fasting blood glucose and glycated haemoglobin A1c) was not associated with increased hearing thresholds. The changes caused by diabetic neuropathy appeared simultaneously with microvascular complications and a long duration of the diabetes, and thus a causative role of diabetic neuropathy in the pathogenesis of elevated hearing thresholds remained unsolved. It was concluded that elevated sensorineural hearing thresholds at the frequencies of 6,000 and 8,000 Hz in patients with IDDM are probably caused by the long duration of diabetes and the microvascular complications associated with it.

Auditory brainstem latencies in type I (insulin-dependent) diabetic patients

INTRODUCTION

This study was undertaken to compare auditory brainstem response latencies in insulin-dependent diabetics, and to compare these findings with metabolic control, microangiopathy, neuropathy, and the duration of diabetes.

METHODS

Auditory brainstem latencies were studied in 53 type I diabetic patients and 42 randomly selected nondiabetic control subjects, aged between 20 and 40 years. Three different stimulus repetition rates (10, 30, and 50 Hz) were used. All subjects had normal hearing ability.

RESULTS

Wave V latencies were longer in diabetic patients when compared with those of control subjects at all repetition rates. At repetition rates of 10 and 50 Hz, diabetic patients had a prolonged I-V interwave latency, and at a repetition rate of 50 Hz, diabetics had a longer III-V interwave latency than control subjects. These findings indicate a central disturbance in the auditory pathway. Microvascular complications (retinopathy, nephropathy) and the duration of diabetes were associated with the prolongation of auditory brainstem latencies. In contrast, poor metabolic control (high fasting blood glucose and glycated hemoglobin A1c) at the time of the present study was only marginally associated with prolonged auditory brainstem latencies. The changes in auditory brainstem latencies associated with diabetic neuropathy (measured with five cardiac autonomic nervous function tests) appeared simultaneously with microvascular complications and in patients with diabetes of long duration, and thus a causative role of diabetic neuropathy in the pathogenesis of prolonged auditory brainstem latencies remains unsolved.

CONCLUSION

Delayed auditory brainstem latencies in type I diabetic patients are probably caused by the long duration of diabetes and the microvascular complications associated with it.

Tympanometry in patients with insulin-dependent diabetes mellitus

Tympanograms were studied in 53 patients with insulin-dependent diabetes mellitus (IDDM) and 42 randomly selected non-diabetic control subjects, aged between 20 and 40 years, using the Madsen Model ZO 73 Impedance Bridge. Subjects with abnormal tympanic membrane, conductive hearing loss and known reason for hearing impairment (e.g. noise damage) were excluded from the study. The mean tympanogram amplitudes in diabetic patients were significantly lower in both ears than those of control subjects. The duration of diabetes and microvascular complications (nephropathy and retinopathy) were associated with decreased amplitudes. These findings indicate that decreased tympanogram amplitudes in patients with IDDM are probably caused by diabetes of long duration and the microvascular complications associated with it.

Tibial nerve somatosensory evoked potentials at various stages of peripheral neuropathy in insulin dependent diabetic patients

To determine whether central nervous conduction deficits are related to the degree of peripheral neuropathy somatosensory evoked potentials (SEP) were measured after tibial nerve stimulation in 51 healthy subjects aged 39.3 (SE 2.0, (range 21-71) years and 100 insulin dependent diabetic patients aged 37.3 (1.5, 18-73) years. Five criteria were used for staging of peripheral neuropathy: nerve conduction; thermal discrimination threshold; vibration perception threshold; tendon reflexes; and neuropathic symptoms. Thirty seven patients had fewer than two abnormalities among the first four criteria and no symptoms (stage 0 = no neuropathy), 37 had 2 or more abnormalities but no symptoms (stage 1 = subclinical neuropathy); 26 had 2 or more abnormalities in conjunction with symptoms (stage 2 = symptomatic neuropathy). Multiple regression analysis was used to define the age and height dependent limits of normal of SEP at the 97.5th and 2.5th centiles. In five patients with stage 1, seven patients with stage 2, but no patient with stage 0 the individual SEP components were unrecordable. The relative frequencies of abnormally prolonged or non-evokable popliteal N8 latency as well as cortical N33 latency and N33/P40 amplitude increased significantly from stage 0 (3-30%) to stage 1 (22-62%) and stage 2 (46-84%) (p < 0.05 for each component and stage). The numbers and percentages of abnormal recordable spinal N22-30 and supraspinal N30-33 interpeak latencies were two (6.3%) and four (11.8%) in patients with stage 0, but these rates did not increase in subjects with stage 1 or 2. The components of SEP were significantly associated with the indices of peripheral and autonomic function tests. There were no major relations between the latencies of SEP and duration of diabetes or prevailing glycaemic control. These findings suggest that the degree of dysfunction along the somatosensory afferent pathways in insulin dependent diabetic patients depends on the stage of peripheral neuropathy; is not related to the degree of glycaemic control or duration of diabetes; and can be characterized mainly by an alteration of the cortical sensory complex and peripheral transmission delay, while spinal and supraspinal conduction deficits are detected infrequently.

Changes in brainstem auditory evoked potentials during insulin-induced hypoglycaemia in type 1 diabetic patients

To determine whether the central and peripheral auditory pathways are disturbed during hypoglycaemia, brainstem auditory evoked potentials were measured in 16 Type 1 diabetic patients aged 17-55 years during intravenous insulin infusion. Within 60 min mean blood glucose declined from 5.0 mmol l-1 to a nadir at 1.7 mmol l-1 followed by an increase to 2.8 mmol l-1 30 min after the insulin infusion had been discontinued. The latency of wave I of brainstem auditory evoked potentials remained unchanged during hypoglycaemia. However, latencies of waves III and V and interpeak latencies I-III, III-V, and I-V were significantly prolonged at average blood glucose levels of 1.7 or 2.1 mmol l-1 when compared with baseline: III 3.96 +/- 0.03 (+/- SE) vs 4.01 +/- 0.04 ms; V 5.69 +/- 0.07 vs 5.81 +/- 0.07 ms; I-III 2.30 +/- 0.05 vs 2.37 +/- 0.05 ms; III-V 1.73 +/- 0.06 vs 1.83 +/- 0.07 ms; and I-V 4.01 +/- 0.05 vs 4.14 +/- 0.06 ms (all p less than 0.05). When blood glucose was allowed to increase to 2.8 mmol l-1, these conduction delays were no longer demonstrable. The depression of the brainstem was approximately paralleled by the activation of counter-regulatory hormones and development of hypoglycaemic symptoms. We conclude that hypoglycaemia results in a rapidly reversible delay of the transmission time in the brainstem but not in the auditory nerve. The dysfunction in the brainstem suggests that not only cortical centres are involved in response to hypoglycaemia in Type 1 diabetic patients.

Evidence for diabetic encephalopathy

Auditory brain stem responses were recorded in 20 normoacoustic long-duration Type 1 diabetic patients (duration of diabetes 26 (range 13-46) years, age 44 (25-66) years) with peripheral neuropathy and retinopathy and in 19 sex-matched normoacoustic short-duration Type 1 diabetic patients (duration of diabetes 2 (0-6) years, age 23 (18-50) years) without clinical signs of neuropathy or microangiopathy. Abnormal brain stem auditory evoked responses were demonstrated in 40% of the long-duration and in 5.3% of the short-duration diabetic patients (p less than 0.01). Interpeak latencies Jv-JI and JIII-JI were significantly prolonged in both patient groups compared with the non-diabetic control group (p less than 0.01). Magnetic resonance imaging was performed in 16 of the long-duration patients and in 40 age-matched healthy volunteers on a whole body MR-scanner. Subcortical and/or brain stem lesions with abnormally high signals were seen in 69% of the long-duration Type 1 patients and in 12% of the healthy volunteers (p less than 0.02). Neuropsychological examination including 17 tests for intelligence and cognition were performed in the 20 long-duration Type 1 diabetic patients. The results indicated a performance close to that seen in a control group of healthy age-matched control subjects. Our study demonstrates that a considerable proportion of long-duration Type 1 diabetic patients suffering from retinopathy and peripheral neuropathy additionally have signs but no symptoms of central nervous system affection, diabetic encephalopathy.

Auditory function in young patients with type 1 diabetes mellitus

Comprehension of the effect of diabetes mellitus on auditory function has been hindered by the fact that previous studies have evaluated hearing function in heterogeneous groups of patients with diabetes mellitus, thus giving conflicting results. We have performed audiometric studies in 46 consecutive patients. 13 with newly diagnosed type 1 diabetes mellitus (group 1) and 33 with type 1 diabetes mellitus of more than 3 years of duration (group 2), of 14 to 40 years of age. The results were compared to an age-matched control group. Pure-tone auditory thresholds were significantly higher in all frequencies 250-8,000 Hz in both groups when compared to the control subjects. Ten patients, all of which belonged to group 2, had auditory thresholds above 30 dB in at least one frequency, showing a conversational hearing loss that ranged between 11 and 44%. However, none of them referred subjective hypoacusia. Univariate analysis revealed significant associations between auditory thresholds and age, duration of disease as well as retinopathy, but not with neuropathy, HbA1c or hypoglycaemic episodes. Only age and duration of disease independently correlated with an auditory threshold using multiple regression. We conclude that type 1 diabetes mellitus can cause mild sensorineural hearing impairment which correlates with age and duration of disease.

Hearing problems and hormonal disturbances in the elderly

The most frequent hormonal diseases attracting audiological interest are hypothyroidism (myxodema) and diabetes mellitus. For many years these diseases have been considered to cause hearing disorders with the lesion located predominantly in the inner ear and central auditory pathways, resulting in sensorineural hearing loss. However, the causal relationship between hearing loss and hypothyroidism has been questioned, and thus a study was undertaken to elucidate this problem. A sample of hypothyroid patients (n = 15) with a median age of 76 years (range 61-92) underwent audiological examination before and after treatment with L-thyroxine (average 5 months; range 2-12), and re-examination (n = 13) after an observation period of average 40 months (range 32-46). No significant improvement in their hearing thresholds, speech reception thresholds or discrimination scores could be demonstrated, and the hearing ability in the hypothyroid patients did not differ significantly from that found in an age- and sex-matched population. In addition, histological investigation of the temporal bones from an 83-year-old woman with myxoedema showed no morphological changes or deposition of glycosaminoglycans. Audiological examinations in patients with insulin-dependent diabetes mellitus also show contradictory results. Therefore, the cochlear and retrocochlear hearing functions were evaluated in 20 patients with diabetic microangiopathy with a median age of 41 years (range 25-66), and in 19 patients without microangiopathy with a median age of 27 years (range 17-42). No significant differences in hearing thresholds or discrimination scores were present between the two diabetic groups, nor was any difference found between the diabetic patients and an age- and sex-matched population. In the patients with long-term insulin-dependent diabetes mellitus, brainstem audiometry revealed abnormal responses in 40%, indicating the presence of diabetic encephalopathy.

Hearing disorders in patients with insulin-dependent diabetes mellitus

The cochlear and retrocochlear hearing function was evaluated in patients with long- and short-term insulin-dependent diabetes mellitus (IDDM) by means of psychoacoustic testing and auditory brain stem responses (ABR). Twenty patients with diabetic microangiopathy (median age 41 years, range 25-66 years) were examined. The median duration of their diabetes was 26 years (range 13-46 years). In addition, 19 patients without microangiopathy (median age 27 years, range 17-42 years) and with a median duration of the diabetes of 2 years (range 0-6 years) were examined. The metabolic control estimated by blood glucose concentration and glycosylated haemoglobin was identical in the two groups of IDDM patients. After correction for age and sex, no significant differences in hearing thresholds or discrimination scores were present between the two diabetic groups, or between the diabetic patients and an age- and sex-matched normal background population. In the patients with long-term IDDM, ABR produced abnormal responses in 40%, indicating the presence of diabetic encephalopathy, whereas ABR were abnormal in only 5% of the patients with short-term IDDM.