Small- and large-fiber involvement in early diabetic neuropathy: a study with the medial plantar response and sensory thresholds

Which combined nerve conduction study scores are best suited for polyneuropathy in diabetic patients?

INTRODUCTION/AIMS

Nerve conduction studies (NCS) are widely used in diagnosing diabetic polyneuropathy. Combining the Z scores of several measures (Z-compounds) may improve diagnostics by grading abnormality. We aimed to determine which combination of nerves and measures is best suited for studies of diabetic polyneuropathy.

METHODS

Sixty-eight patients with type 1 diabetes and 35 controls were included in this study. NCS measurements were taken from commonly investigated nerves in one arm and both legs. Different Z-compounds were calculated and compared with reference material to assess abnormality. A sensitivity proxy, the accuracy index (AI), and Cohen's d were calculated.

RESULTS

Z-compounds with the highest AI consisted of the tibial and peroneal motor, and the sural, superficial peroneal, and tibial medial plantar sensory nerves in one or two legs. All Z-compounds were able to discriminate between diabetic subjects and nondiabetic controls (mean Cohen's d = 1.42 [range, 1.03-1.63]). The association between AI and number of measures was best explained logarithmically (R²  = 0.401), with diminishing returns above approximately 14 or 15 measures. F-wave inclusion may increase the AI of the Z compounds. Although often clinically useful among the non-elderly, the additional inclusion of medial plantar NCS into Z-compounds in general did not improve AI.

DISCUSSION

Performing unilateral NCS in several motor and sensory lower extremity nerves is suited for the evaluation of polyneuropathy in diabetic patients. The use of Z-compounds may improve diagnostic accuracy in diabetic polyneuropathy and may be particularly useful for follow-up research studies as single summary measures of NCS abnormality development over time.

Early Detection of Diabetic Peripheral Neuropathy: A Focus on Small Nerve Fibres

Diabetic peripheral neuropathy (DPN) is the most common complication of both type 1 and 2 diabetes. As a result, neuropathic pain, diabetic foot ulcers and lower-limb amputations impact drastically on quality of life, contributing to the individual, societal, financial and healthcare burden of diabetes. DPN is diagnosed at a late, often pre-ulcerative stage due to a lack of early systematic screening and the endorsement of monofilament testing which identifies advanced neuropathy only. Compared to the success of the diabetic eye and kidney screening programmes there is clearly an unmet need for an objective reliable biomarker for the detection of early DPN. This article critically appraises research and clinical methods for the diagnosis or screening of early DPN. In brief, functional measures are subjective and are difficult to implement due to technical complexity. Moreover, skin biopsy is invasive, expensive and lacks diagnostic laboratory capacity. Indeed, point-of-care nerve conduction tests are convenient and easy to implement however questions are raised regarding their suitability for use in screening due to the lack of small nerve fibre evaluation. Corneal confocal microscopy (CCM) is a rapid, non-invasive, and reproducible technique to quantify small nerve fibre damage and repair which can be conducted alongside retinopathy screening. CCM identifies early sub-clinical DPN, predicts the development and allows staging of DPN severity. Automated quantification of CCM with AI has enabled enhanced unbiased quantification of small nerve fibres and potentially early diagnosis of DPN. Improved screening tools will prevent and reduce the burden of foot ulceration and amputations with the primary aim of reducing the prevalence of this common microvascular complication.

Correlation of retinal neurodegeneration with measures of peripheral autonomic neuropathy in type 1 diabetes

Purpose

To evaluate the relationship of neuroretinal layer thickness with sensitive measures of cardiovascular autonomic neuropathy in diabetic patients with non‐proliferative diabetic retinopathy (NPDR).

Methods

Twenty‐seven eyes of 27 patients with type 1 diabetes presenting with mild‐to‐moderate NPDR were compared to 27 healthy control (HC) eyes matched for age and gender. The total macular volume (TMV) and the volumes of individual neurosensory layers in the macula were analysed from spectral domain optical coherence tomography using automated layer segmentation. Cardiovascular autonomic regulation was assessed by short‐term power spectrum analysis of heart rate variability (HRV) before, during and after an orthostatic challenge.

Results

The patients had an age of 46 ± 12 years and diabetes since 28 ± 9 years. Diastolic and mean arterial pressure was lower in the patients compared to HCs. TMV (r = 0.58, p = 0.002), inner plexiform layer volume (IPLV; r = 0.39, p = 0.047) and inner nuclear layer volume (INLV; r = 0.60, p = 0.001) were associated with reduced recovery of low‐frequency (LF) spectral power of HRV after orthostatic load in diabetic patients but not in HCs. The response of LF spectral power during the orthostatic manoeuvre was blunted in patients compared to HCs (p = 0.02). Diabetes duration was negatively associated with TMV and INLV, whereas IPLV was significantly reduced in eyes with moderate NPDR compared to HCs.

Conclusion

The results indicate a correlation between inner retinal tissue loss and diminished autonomic regulation in type 1 diabetic patients with mild‐to‐moderate NPDR. The observed changes can be interpreted as congruent early signs of retinal and systemic neuropathy in diabetes.

Evaluation of Nerve Conduction Studies in Obese Children With Insulin Resistance or Impaired Glucose Tolerance

The aim of the study was to investigate nerve conduction studies in terms of neuropathic characteristics in obese patients who were in prediabetes stage and also to determine the abnormal findings. The study included 69 obese adolescent patients between April 2009 and December 2010. All patients and control group underwent motor (median, ulnar, tibial, and peroneal) and sensory (median, ulnar, sural, and medial plantar) nerve conduction studies and sympathetic skin response test. Sensory response amplitude of the medial plantar nerve was significantly lower in the patients with impaired glucose tolerance and insulin resistance. To our knowledge, the present study is the first study demonstrating the development of sensory and autonomic neuropathy due to metabolic complications of obesity in adolescent children even in the period without development of diabetes mellitus. We recommend that routine electrophysiological examinations be performed, using medial plantar nerve conduction studies and sympathetic skin response test.

Sensitivity and specificity of a new test for thermographic evaluation of the foot in the diagnosis of diabetic peripheral polyneuropathy

OBJECTIVE

This work determined the sensitivity, specificity, and predictive values of a test evaluating the thermal perception threshold to cold and heat and established a thermal interval with the participant's basal temperature in order to detect diabetic peripheral neuropathy in 172 people with diabetes, 86 with and 86 without diabetic neuropathy.

DESIGN

This was a cross-sectional, diagnosis accuracy study.

SETTING

This research was performed from January 2010 to February 2012 in Seville, Spain, and Córdoba, Spain.

PARTICIPANTS

One hundred seventy-two people with diabetes, 86 with and 86 without diabetic neuropathy, were recruited to participate in the study.

MAIN OUTCOME MEASURES

The thermal sensitivity was examined in the participants' feet with an instrument designed to assess thermal discrimination and sensitivity based on the Peltier principle. The skin temperature was recorded, and it was performed the following tests: (1) determining the thermal discrimination threshold, used to identify the lowest noticeable temperature difference, and (2) examining the thermal sensitivity, used to determine the absolute thermal threshold. The receiver operating characteristic curve technique was used to calculate the sensitivity, specificity, and predictive values.

MAIN RESULTS

The area under the curve that showed the best sensitivities and specificities bilaterally was for the warm temperatures under the first and fifth metatarsal heads. In these zones, the temperature difference needed to predict whether a patient was neuropathic was 2°C. Sensitivities were greater than 75%, and the positive predictive values in all cases exceeded 60%.

CONCLUSIONS

This technique enabled the authors to quantify the degrees of colder or warmer temperature differences that participants with diabetes (with and without neuropathy) needed to be able to detect a difference, with acceptable sensitivity, specificity, and predictive values.

Temperature threshold testing: a systematic review

The diagnosis of small fiber neuropathy (SFN) has been recently defined as typical symptoms due to small nerve fiber dysfunction accompanied by reduced intra-epidermal nerve fiber density (IENFD) or abnormal temperature threshold testing (TTT). Guidelines have been published for the assessment of IENFD. However, international guidelines for TTT are lacking. This paper presents a systematic literature review on reported TTT methods and provides recommendations for its future use in studies evaluating patients. A total of 164 papers fulfilled pre-defined requirements and were selected for review. Over 15 types of instruments are currently being used with a variety of methodological approaches for location, stimulus application, and sensation qualities examined. Consensus is needed to standardize the use of TTT as a diagnostic and follow-up tool in patients.

Thermal threshold: research study on small fiber dysfunction in distal diabetic polyneuropathy

OBJECTIVE

The most commonly used technique for diagnosis of diabetic neuropathy (DN) is nervous conduction (NC). Our hypothesis is that the use of the thermal threshold (TT) technique to evaluate small fiber damage, which precedes large fiber damage, could enable earlier diagnosis and diminish false negatives.

RESEARCH DESIGN AND METHODS

The study involved 70 asymptomatic patients with type 2 diabetes mellitus (T2DM) all being treated with oral hypoglycemic medication, and having negative metabolic control levels with glycosylated hemoglobin A1c greater than 7% and less than 8%. Diabetic neuropathy was their only evident complication. All other complications or other causes of neuropathy were discarded. Their time of evolution was 1 to 48 months since date of diagnosis of diabetes. Both thermal threshold and sensory and motor nervous conduction were determined in upper and lower limbs.

RESULTS

Nervous conduction was found normal in 81% and altered in 19% of patients (large fiber neuropathy). Thermal threshold was normal in 57% and altered in 43% of patients (small fiber neuropathy). In those with normal TTs, no case with an altered NC was found (p < 0.001). Patients with altered TTs could have normal (57%) or altered NC (43%). Thus, NC showed a high frequency of false negatives for DN (57% of 30 cases). The frequency of small fiber neuropathy found with the TT test was higher than that of large fiber neuropathy found with the NC test (p < 0.001) and was found at an earlier age.

CONCLUSIONS

The TT test demonstrated a higher frequency of neuropathy than the NC test in clinically asymptomatic T2DM patients. We suggest that small fiber should be studied before large fiber function to diagnosis distal and symmetrical DN.

The prevalence of peripheral neuropathy in a population-based study of patients with type 2 diabetes in Sweden

AIMS

To assess peripheral neuropathy following a standardized foot examination protocol in a representative population-based cohort of subjects with type 2 diabetes.

METHODS

In a geographically defined population, aged 40-70 years with diabetes prevalence of 3.5% according to medical records, we investigated 156 type 2 diabetic subjects, 95% Caucasian, mean age 61.7±7.2 years, duration of diabetes 7.0±5.7 years, and HbA(1c) 7.3±2.4% (6.4% Mono-S), by questionnaires, clinical examinations, blood sampling, and review of medical records. Foot examination included clinical signs of peripheral neuropathy and tests of sensibility with monofilament, tuning fork, and assessments of the vibration perception thresholds (VPT).

RESULTS

Peripheral autonomic neuropathy (PAN) as judged by two or more signs of dysfunction was the most common and affected 43%. The prevalence of peripheral sensory neuropathy (PSN) was 15% by monofilament, 24% by tuning fork, and 28% by VPT expressed as ZscoreVPT ≥2.0 S.D. Twenty-nine percent had a VPT ≥25 V. Signs of peripheral motor neuropathy (PMN) affected 15%. Peripheral neuropathy, at least one variable, affected 67%, whereas 25% were affected by more than one variable of neuropathy, i.e., polyneuropathy. Exclusion of other identified causes for neuropathy than diabetes reduced the prevalence of diabetic polyneuropathy to 23%. Concurrent diabetic complications were 29% for retinopathy, 14% for incipient nephropathy, and 8% for overt nephropathy. The prevalence of macrovascular complications was 62% for CVD, 26% for PVD, and 11% for cerebrovascular lesion (CVL).

CONCLUSION

Peripheral neuropathy was common in this representative type 2 diabetes population. Clinical signs of PAN were the most frequent followed by diminished perception of vibration and touch.

Vibrotactile sense in median and ulnar nerve innervated fingers of men with Type 2 diabetes, normal or impaired glucose tolerance

AIMS

To investigate vibrotactile sense (large fibre neuropathy) at different frequencies in index and little fingers (median and ulnar nerves, respectively) of subjects with diabetes, or impaired (IGT) or normal glucose tolerance (NGT).

METHODS

Vibration thresholds (tactilometry at seven frequencies (8, 16, 32, 64, 125, 250 and 500 Hz)) and median nerve function (electrophysiology) were examined in men (age 73.4 +/- 0.12 years; n = 58, mean +/- sd) with persistent NGT (n = 28) or IGT (n = 7) or with Type 2 diabetes mellitus (T2DM) (n = 23) for > 15 years.

RESULTS

HbA1c was increased and vibrotactile sense (sensibility index) was impaired in index and little fingers in men with T2DM. Vibration thresholds were particularly increased at 16, 250 and 500 Hz in the little finger (ulnar nerve). T2DM subjects showed electrophysiological (gold standard) signs of neuropathy in the median nerve. Although subjects with persistent IGT had higher HbA1c, vibrotactile sensation and electrophysiology remained normal. HbA1c did not correlate with vibrotactile sense or electrophysiology, but the latter two correlated with respect to Z-score (sign of neuropathy) in forearm (NGT) and at wrist level (NGT and DM).

CONCLUSIONS

Vibration thresholds are increased in the finger pulps in T2DM subjects, particularly at specific frequencies in ulnar nerve innervated finger pulps. Neuropathy is not present in IGT. Tactilometry, with a multi-frequency approach, is a sensitive technique to screen for large fibre neuropathy in T2DM. Frequency-related changes may mirror dysfunction of various receptors.

Diagnostic role of deep tendon reflex latency measurement in small-fiber neuropathy

Small-fiber neuropathy (SFN) is diagnosed on the basis of clinical features and specialized tests of small-fiber function because standard nerve conduction studies are normal. Thus, the objective of this study was to determine the value of deep tendon reflex (DTR) latency measurement in the diagnosis of SFN in patients with preserved DTR on clinical examination. We prospectively examined electromyographic reflexes from the biceps brachii [biceps brachii reflex (BR)], patellar [patellar reflex (PR)], and ankle [ankle reflex (AR)] using a manually operated electronic reflex hammer attached to electromyography machine and recorded by means of surface electrodes in 18 patients with SFN and 38 controls. Intra- and inter-evaluator reliability was good (intraclass correlation coefficient: 0.80-0.91, p < 0.01). In controls, the latencies at all sites were correlated to the height (R= 0.6, p < 0.01). Compared with controls, in patients with SFN, the mean latency in milliseconds was prolonged at all sites (BR: 12.8 +/- 1.6 vs. 8.9 +/- 1.9, p < 0.01; PR: 23.0 +/- 5.8 vs. 17.4 +/- 2.4, p < 0.01; and AR: 34.5 +/- 4.8 vs. 30.0 +/- 2.4, p < 0.01). The sensitivity [61.1% (95% CI: 51-94.9)] and specificity [92% (95% CI: 73-97.3)] of BR latency were roughly equal to those of PR and AR. We conclude that DTR latencies were significantly abnormal in the majority of the patients with SFN, suggestive of subclinical involvement of large myelinated fibers. DTR latency measurement is a reproducible, valuable, sensitive tool in the evaluation of mild subclinical involvement of large fibers.

Medial plantar nerve conduction studies in healthy controls and diabetics

OBJECTIVE

To collect a reference material of the medial plantar nerve action potential, to test intra/interobserver reliability in healthy controls and to apply the test to a group of patients with diabetes mellitus.

METHODS

98 healthy controls and 50 patients with diabetes mellitus were included. The medial plantar nerve was stimulated orthodromically and recorded with a surface electrode. In the patient group, NCS of motor and sensory nerves and quantitative sensory testing were also performed.

RESULTS

Responses of the medial plantar nerve were obtained from all controls except from one aged 72. Amplitude decreased with age (r=-0.68, p<0.0001). Intra/interobserver reliability was acceptable. 52% of the patients had abnormal overall NCS classification. Forty-eight percent had delayed tibial F-response latency. The medial plantar NCS were abnormal in 59% of the cases (47% abnormal NAP amplitude and 39% reduced CV), 59% of those with abnormal NCS had symptoms of sensory polyneuropathy. Only 24% had abnormal sural amplitude. Cold perception threshold was abnormal in more patients (30%) than warmth perception threshold (14%).

CONCLUSIONS

Responses were easily obtained in controls under 70 years. In diabetics the amplitudes of the medial plantar nerve were abnormal more often than in the sural nerve.

SIGNIFICANCE

The medial plantar nerve response is reliable in patients under 70 years, and intra/interobserver reliability is acceptable.

Cutaneous thermal sensitivity in diabetic neuropathy

BACKGROUND

The goal of this investigation was to determine if cutaneous thermal sensitivity could be used as a discriminator of peripheral neuropathy in diabetic subjects who were sensate to the Semmes-Weinstein 5.07 monofilament.

METHODS

Sixty adult subjects were separated into two groups. The control group (A) was composed of 30 young healthy individuals without a history of diabetes. The focus group (B) was composed of 26 individuals with adult onset diabetes and four with juvenile onset. All of the subjects underwent thermal sensitivity testing in peripheral nerve root dermatomes of their hands and feet. Testing was performed with custom devices fabricated from materials with different thermal conduction capacities (copper, steel, glass, and plastic). Similar tests were performed with glass tubes containing heated or cooled water to develop a range of thermal sensitivity for the subjects.

RESULTS

There was a strong relationship between cold perception and stimulation with the copper probe in dermatomes of the radial nerve of the upper limb and the superficial peroneal dermatome of the lower limb.

CONCLUSIONS

Thermal sensitivity to copper and cold stimulation may be more discriminative and have a higher threshold than sensitivity to the Semmes-Weinstein monofilament. This simple method may have a role in the early detection of peripheral neuropathy in adult-onset diabetes mellitus.

Exploration of small fibers for testing diabetic neuropathies

INTRODUCTION

Electrophysiological exploration of neuropathies is a standard method of investigating the dysfunction of myelinated larger fibers (Aalpha, Abeta). However, this method cannot test dysfunctions in other fibers. To evaluate the smaller (Adelta) and unmyelinated fiber (C-fibers) lesions a quantitative method has been perfected: the study of the sensory thresholds (quantitative sensory testing: QST). It allows the investigation of the sensory symptoms and is a reproducible, non-invasive and painless method. It is used above all in patients suffering from diabetic neuropathy ('Diabetes Care 9 (1987) 432').

PATIENTS AND METHODS

We used the QST testing in comparison with nerve conduction velocities in 40 Non-Insulin-Dependent Diabetes Mellitus (NIDDM or Type II) patients in their 60s (+/-10 years). Depending on the duration of their diabetes (dd), we distinguished three groups: dd < 5 years (GI) dd from 5 to 15 years (GII) and dd > 15 years (GIII). All the patients underwent a clinical neurological examination, which enabled us to establish a gravity score comparable to the NDS (Neuropathy Disability Score: 'Muscle Nerve 10 (1988) 21').

RESULTS

Nerve conduction velocities and QST were studied for each group of patients. Electrophysiological alterations were connected to the gravity clinical score and in some asymptomatic patients a higher QST heat threshold could be observed.

DISCUSSION

These results indicate that QST can detect the early dysfunction of the unmyelinated fibers in this kind of neuropathy. Subclinical detection can reduce severe neurological complications and make possible an early and effective treatment.

Technology literature review: quantitative sensory testing

The development of the personal computer has simplified the process of quantitating sensory thresholds using various testing algorithms. We reviewed the technical aspects and reproducibility of different methods to determine threshold for light touch-pressure, vibration, thermal, and pain stimuli. Clinical uses and limitations of quantitative sensory testing (QST) were also reviewed. QST is a reliable psychophysical test of large- and small-fiber sensory modalities. The results of QST are highly dependent on methodology and the full cooperation of the subject. QST has been shown to be reasonably reproducible over a period of days or weeks in normal subjects. The use of QST in research and patient care should be limited to instruments and their corresponding methodologies that have been shown to be reproducible. Literature data do not allow conclusions regarding the relative merits of individual QST instruments.

Experimental diabetes accelerates accumulation of fluorescent pigments in rat trigeminal neurons

The purpose of this study was to investigate autofluorescent pigment granules (lipofuscin, ceroid) in the trigeminal neurons (TN) during aging and streptozotocin-induced diabetes. Four young adult male rats were injected with streptozotocin (STZ; 50 mg/kg) to produce diabetes (DM), for comparison with four young uninjected control rats and four aged rats (90 weeks old). Eight weeks after STZ injection, all rats were fixed with 4% paraformaldehyde, and paraffin sections of TN were prepared and observed by fluorescence microscopy. We found the number of neurons with autofluorescent pigments had increased to 30.38% of the total in DM compared to 8.98% in the control group, and 25.36% in the aged rats. The area of autofluorescence within those neurons was 16.84% in aged rats, 13.02% in DM and 4.45% in the controls. Thus, DM caused accelerated accumulation of fluorescent granules in trigeminal neurons, and this change may show that premature aging contributes to neuronal functional decline and morphological change.

Quantitative sensory testing

Quantitative sensory testing is a reliable way of assessing large and small sensory nerve fiber function. Sensory deficits may be quantified and the data used in parametric statistical analysis in research studies and drug trials. It is an important addition to the neurophysiologic armamentarium, because conventional sensory nerve conduction tests only the large fibers. QST is a psychophysical test and lacks the objectivity of NCS. The results are subject to changes owing to distraction, boredom, mental fatigue, drowsiness, or confusion. When patients are consciously or unconsciously biased toward an abnormal QST result, no psychophysical testing can reliably distinguish these patients from those with organic disease. QST tests the integrity of the entire sensory neuraxis and is of no localizing value. Dysfunction of the peripheral nerves or central nervous system may give rise to abnormalities in QST. As is true for other neurophysiologic tests, QST results should always be interpreted in light of the patient's clinical presentation. Quantitative sensory testing has been shown to be reasonably reproducible over a period of days or weeks in normal subjects. Because longitudinal QST studies of patients in drug trials are usually performed over a period of several months to a few years, reproducibility studies on the placebo-control group should be included. For individual patients, more studies are needed to determine the maximum allowable difference between two QSTs that can be attributed to experimental error. The reproducibility of thermal thresholds may not be as good as that of vibration threshold. Different commercially available QST instruments have different specifications (thermode size, stimulus characteristics), testing protocols, algorithms, and normal values. Only QST instruments and their corresponding methodologies that have been shown to be reproducible should be used for research and patient care. The data in the literature do not allow conclusions regarding the superiority of any QST instruments. The future of QST is promising; however, many factors can affect QST results. As is true for other neurophysiologic tests, QST is susceptible to many extraneous factors and to misuse when not properly interpreted by the clinician.

Interdigital nerve conduction study of the foot for an early detection of diabetic sensory polyneuropathy

OBJECTIVE

To report on the value of interdigital nerve (IDN) conduction study (NCS) of the foot for the recognition of diabetic sensory polyneuropathy with normal routine NCS and the nature of electrophysiological abnormality in early diabetic sensory polyneuropathy.

METHODS

The sensory nerve conductions in the two digital and 4 IDNs of the foot were obtained orthodromically using the near-nerve needle and signal averaging technique.

RESULTS

In 21 patients with diabetic sensory polyneuropathy with normal routine NCS, a definite neuropathy pattern (abnormalities in more than 3 of 6 tested nerves) was observed in 12 patients (57.1%). The most common abnormalities that were found were a low amplitude in the sensory compound nerve action potential and an absent potential, indicating that early diabetic sensory polyneuropathy is due to axonal degeneration.

CONCLUSIONS

Interdigital NCS of the foot using near-nerve needle technique can identify neuropathy in diabetic sensory polyneuropathy with normal routine NCS. This technique offers a useful means of detecting nerve conduction abnormalities in the early stage of diabetic polyneuropathy.

Vibration perception threshold testing in patients with diabetic neuropathy: ceiling effects and reliability

AIMS

To test the reliability of a new vibrometer (Maxivibrometer) which was constructed so that vibration perception threshold (VPT) could be determined without the disadvantage of the off-scale measurements frequently experienced with the Biothesiometer.

METHODS

The two devices were compared and tested on a group of diabetic neuropathic subjects and a group of healthy, matched control subjects. VPT was tested on the plantar surface of the feet.

RESULTS

The Maxivibrometer gave an actual measurement in all cases even if subjects were severely neuropathic. The replication-to-replication and day-to-day intraclass correlation coefficients for the Maxivibrometer VPT were, except in one case, above 0.94, indicating excellent reliability. The Biothesiometer VPT could also be measured with excellent reliability but only within a limited range of mild to moderate neuropathy, so it appears to be an appropriate screening tool. The replication-to-replication intraclass correlation coefficient was 0.93.

CONCLUSIONS

Because VPT could be measured over a wide range with the Maxivibrometer, it was demonstrated that loss of sensation in diabetic neuropathy can progress far beyond the maximum VPT value of the Biothesiometer. The wide measurement range and the excellent reliability make the Maxivibrometer a valuable research tool to quantify loss of sensation, particularly in the presence of severe neuropathy and to record changes over time. Diabet. Med. 18, 469-475 (2001)

Pain threshold measurements with cutaneous argon laser, comparing a forced choice and a method of limits

1. With the argon laser technique cutaneous nociceptors can be activated with high specificity and reproducibility making it a useful tool in psychophysical pain studies. This study was designed to examine and compare two different psychophysical methods combined with the argon laser technique. 2. Pain thresholds on different locations of the body and on different skin types were measured with (i) the method of limits and (ii) the forced choice method. 3. A significant correlation between the pain thresholds measured with the two different methods was detected on feet and hands. The method of limits yielded significantly higher pain thresholds in glabrous skin than hairy skin. Higher pain thresholds were also detected on the right side of the body. No statistically significant difference between sexes was found. A high reproducibility over time as well as in-between investigators was found for the method of limits. 4. Its concluded that the argon laser for pain threshold measurement with the method of limits is useful and preferred to the forced choice, since the method of limits is easier to perform and also less time consuming.

Dysfunction of small myelinated afferents in diabetic polyneuropathy, as assessed by laser evoked potentials

OBJECTIVE

To verify whether laser evoked potentials are useful in assessing the function of small afferent fibers and to compare dysfunction of large and small afferent fibers in patients with diabetic polyneuropathy.

METHODS

The brain potentials evoked by CO2 laser stimulation of the hand and foot were studied in diabetic patients (n = 45) with various degrees of peripheral nerve damage. Laser evoked potentials (which assess the function of small myelinated afferents) were also compared with ulnar and sural nerve sensory action potentials (which assess the function of large myelinated afferents) by scoring the abnormalities of the two neurophysiological tests with similar criteria.

RESULTS

Laser evoked potentials were often absent; the mean latency was normal and mean amplitude decreased, as expected in axonopathies. Although clinical examination showed more frequent impairment of vibratory than pinprick sensation, laser evoked potentials and sensory action potentials yielded similar abnormality scores and showed a strong intra-individual correlation.

CONCLUSIONS

Laser evoked potentials, possibly better than standard clinical examination for assessing the abnormalities of small-diameter afferents, indicate that diabetic polyneuropathy induces large- and small-afferent dysfunction in parallel.

Peripheral neuropathies in diabetes

Peripheral neuropathy in diabetes remains a difficult management dilemma. The clinical manifestations may vary widely. Polyneuropathies develop with increasing duration of disease, and a thorough understanding of the clinical manifestations, including sensory, motor, and autonomic deficiencies, helps guide diagnosis and treatment. A multidisciplinary approach emphasizing preventive care and timely intervention can decrease morbidity significantly and improve the quality of life for the patient. Properly fitting shoes and avoidance of foot trauma are cornerstones of preventive management. Strict control of serum glucose can alter the course of peripheral neuropathies. This control can be accomplished with a strict insulin regimen or pancreatic transplant. Further research is needed to increase knowledge about peripheral neuropathies in diabetes and aid the physician with new treatment options.

Clinical applications of quantitative sensory testing (QST)

Quantitative sensory testing (QST) has been used clinically for the last two decades, yielding a substantial number of publications regarding these applications. In this review we tried to amass together the major findings of these publications into one monograph, excluding those dealing with pain. This was done with the aim of assisting clinicians in the better use of QST techniques for the benefit of their patients.

Quantitative measurement of cutaneous perception in diabetic neuropathy

To determine the diagnostic value of various cutaneous sensory modalities in diabetic neuropathy, we studied cutaneous perception at the dominant hallux of 113 subjects (32 normal healthy controls and 81 diabetic subjects). The cutaneous sensory perception tests included warm and cold thermal perception, vibration, touch-pressure sensation, and current perception testing (CPT). The sensitivity of each modality when specificity is held greater than 90% was as follows: warm = 78%, cold = 77%, vibration = 88%, tactile-pressure = 77%, 5-Hz CPT = 52%, 250-Hz CPT = 48%, and 2000-Hz CPT = 56%. Combination thermal and vibratory gave optimum sensitivity (92-95%) and specificity (77-86%). We conclude that vibratory and thermal testing should be the primary screening tests for diabetic peripheral neuropathy. Other modalities may be of use only in specific situations.

The value of the Neurometer in assessing diabetic neuropathy by measurement of the current perception threshold

The Neurometer is a relatively new device for assessing neuropathy by measuring current perception threshold (CPT). The study aim was to assess the ability of the Neurometer to distinguish between different types of nerve fibre damage by using different frequencies (2000 Hz, 250 Hz, and 5 Hz) of electric stimulus (high frequencies for large fibres and low frequencies for small fibres) and comparing the results with standard sensory tests of vibration perception threshold (VPT) and thermal perception threshold (TPT). CPT was determined on index finger and great toe of 51 patients with diabetic neuropathy and 28 non-diabetic control subjects, age and sex matched. CPT in neuropathic patients could be distinguished from controls at all three frequencies in both feet and hands (p < 0.05). The best correlation was found between CPT at 2000 Hz and VPT (r = 0.48, p < 0.001) in the feet suggesting a degree of neuroselectivity. Internal correlations between CPT at the three frequencies showed the weakest correlation between CPT at 2000 Hz and 5 Hz (r = 0.27, p < 0.005), suggesting also that possibly different types of fibres were examined. CPT reproducibility was better in control (CV = 6.4-27.7%), than in neuropathic subjects (CV = 28.4-52.3%), although the coefficient of variation was comparable to that of standard tests of sensory function, VPT and TPT. The Neurometer is a simple instrument to use in clinical practice. It has a degree of neuroselectivity but like all subjective sensory tests has a large variability.

Nerve growth factor (NGF) restores depletions of calcitonin gene-related peptide and substance P in sensory neurons from diabetic mice in vitro

Dorsal root ganglion neurons from streptozotocin (STZ)-induced diabetic, genetic diabetic and normal mice were cultured in serum-containing media with or without nerve growth factor (NGF). The immunocytochemical analysis carried out after 1 week in culture revealed that the ratios of neurons immunoreactive to calcitonin gene-related peptide (CGRP) in NGF-free medium in the STZ-diabetic mice (average 23.2%) were significantly lower than those in the normal mice (45.1%). The ratios of neurons immunoreactive to CGRP and substance P (SP) in the NGF-free medium were also lower in the genetic diabetic mice (23.6% and 21.8%) than those in the normal ones (40.7% and 34.2%). However, treatment with NGF restored these reduced immunoreactivities in the diabetic groups in a dose-dependent manner. These results show that NGF can be effective for the diabetes-induced depletion of CGRP and SP in sensory neurons, and suggest its possible role in the prevention and improvement of diabetic sensory neuropathy.

The effect of prostaglandin E1.alpha CD on vibratory threshold determined with the SMV-5 vibrometer in patients with diabetic neuropathy

We studied the effect of prostaglandin E1.alpha CD (PGE1) on diabetic peripheral neuropathy by evaluating subjective symptoms and vibration sensation using a new vibrometer (SMV-5). Patients with diabetic neuropathy (n = 38) were divided into three groups; group A received no drugs (control), group B was treated with 1500 micrograms/day of oral methyl vitamin B12 (VB12) for four weeks, and group C received 1.2 micrograms/kg/day PGE1 intravenously for four weeks. There was a close relationship between symptom scores and vibratory threshold (VT). The effect of PGE1 on subjective symptoms and VT were compared with those in groups A and B. Patients who received PGE1 showed a significant improvement rate in pain and hypesthesia compared to patients in groups A and B, and in numbness compared to group A. During the study period, there was no significant change in VT in groups A and B, whereas VT was significantly improved at styloid process (P < 0.05) and at medial malleolus (P < 0.001) in group C. Our results confirmed that PGE1 significantly improved both subjective symptoms and VT, indicating that PGE1 therapy may be useful in diabetic neuropathy.

Sensory thresholds in older adults: reproducibility and reference values

To evaluate the test-retest reproducibility of vibratory perception (VPT) and thermal discrimination (TDT) thresholds on the foot in older adults, we examined 20 50-76-year-old subjects with, and 19 without non-insulin-dependent diabetes mellitus. Adjusted reference values for both thresholds were obtained by assessing the relations with age, body height, and sex among 216 subjects with normal glucose tolerance, of the same age, sampled randomly from a geographically defined general population. The VPT appeared to be more reproducible than the TDT (reliability coefficient 0.89 vs. 0.54). The reproducibility of the VPT was inversely related to age and better for men than for women. Diabetes and glycemic level did not affect the reproducibility of either threshold. Both thresholds were related to age and height. Women had a higher VPT than men. The relations between sex and sensory thresholds at the lower limb, reported in previous studies, were probably confounded by height.

Subclinical diabetic polyneuropathy: early detection of involvement of different nerve fibre types

Nerve conduction studies, tests of autonomic function and terminal nerve branches, and soleus muscle H reflexes were applied to 60 patients with insulin dependent diabetes mellitus who had no clinical symptoms but abnormal vibratory or temperature perception thresholds indicating subclinical neuropathy. In most patients neurophysiological examination yielded a broad spectrum of neural dysfunction. The perception threshold for cold stimuli was sometimes selectively impaired and abnormal pupillometry results were common, suggesting that small fibres are vulnerable in the early stage of diabetic neuropathy. The arms were less frequently and less severely affected than the legs, an effect that may be related to nerve length. The neurophysiological test results did not change in 30 patients followed up for one year.

Association of thermal perception thresholds with cardiovascular autonomic function in diabetes

In order to study the association between warm thermal-perception thresholds (WPT), cold thermal-perception thresholds (CPT) and cardiovascular autonomic function, we examined 91 otherwise healthy patients with diabetes mellitus (69 with type I and 22 with type II). The covariance analysis revealed that WPT was associated with the deep-breathing E/I ratio and the Valsalva ratio (p = 0.004 and p = 0.008, respectively) whereas CPT was associated with the Valsalva ratio and the postural blood pressure decrement (p = 0.008 and p = 0.004, respectively). These associations possibly reflect histological similarities between the parasympathetic nerves and those mediating warm sensation, and between the sympathetic nerves and those mediating cold sensation.

Portable infrared pupillometry using Pupilscan: relation to somatic and autonomic nerve function in diabetes mellitus

The relationship between dynamic pupillary function and peripheral nerve function was studied in 85 randomly-selected diabetic patients and 67 age-matched normals using a portable infrared pupillometer (Pupilscan Version 5). Seven measurements were chosen to represent different components of the pupillary constriction-redilatation curve after a standardized light stimulus. Constriction latency was significantly prolonged in diabetic patients (p = 0.05), as was time to 63% redilatation (p = 0.001). Thermal thresholds at the feet weakly correlated with relative reflex amplitude (warm: r = -0.22, p = 0.05; cool: r = -0.23, p = 0.05), but vibration perception thresholds were more strongly associated with constriction and redilatation velocity (r = -0.42, p = 0.001; r = -0.28, p = 0.03). Among the cardiovascular autonomic function tests, only respiratory R-R variation correlated with constriction velocity (r = 0.47, p < 0.001), and Valsalva ratio with redilatation velocity (r = 0.25, p = 0.04), but postural systolic blood pressure change was also correlated with reflex amplitude and latency time (r = -0.42, p < 0.001; r = 0.41, p = 0.001). There were no significant associations with three measures of sweating function in the feet. Pupil measurements were abnormal in 4-11% of diabetic patients, while other neurological tests were abnormal in 8-35%, consistent with the length-dependence of diabetic neuropathy. Median coefficients of variation were 2.0-7.2% in diabetic patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitative measures of sympathetic skin response in diabetes: relation to sudomotor and neurological function

The sympathetic skin response (SSR) at the foot to a deep inspiration was measured in 68 randomly selected diabetic patients and 46 age matched normal subjects and compared with other quantitative measures of neurological and sudomotor function. SSR was obtained in all but three diabetic patients. The upper limit of normal for the onset latency was 2202 ms and the lower limit for the amplitude of the first wave 92 microV. Ten diabetic patients had measurable but prolonged latencies, and 11 had measurable but low amplitudes. There were no significant associations between latency, height, and age, but in insulin dependent patients there was a significant diminution of response amplitude with increasing duration of diabetes. Latency was weakly associated with Marstock thermal thresholds, respiratory RR variation, and common peroneal nerve conduction velocity. SSR amplitude was associated with the density of pilocarpine activatable sweatspots in the same region of the foot. Patients with abnormal latencies were significantly older and had reduced thermal sensation than those with normal latencies. Median coefficients of variation for repeat testing in diabetic patients were 9% for latency and 13% for amplitude. The test is objective and reproducible, but latency measurements reflect conduction in a long multineuronal pathway and are not purely a measure of peripheral C fibre function; amplitude measurements reflect the density of spontaneously activable sweat glands and are therefore a valid measure of peripheral sympathetic activity, though they depend more on temperature than do latencies (mean change over the range 32-34 degrees C; 8.5% degrees C for amplitude, -2.5%/degrees C for latency).

Thermal threshold testing for the assessment of small fibre dysfunction: normal values and reproducibility

Small and large fibre neuropathy are common findings in patients with long-standing diabetes mellitus. The Thermal Threshold Tester was tested to obtain normal values for thermal perception threshold for warmth and cold. This device produces thermal stimuli by means of a Peltier element placed on the skin. Warm and cold thresholds are measured using a forced choice method with an up-and-down-transform rule and expressed in degrees Celsius (degree C). Thresholds were measured at the right wrist and right foot in 80 normal subjects, divided into four age groups; 25-34, 35-44, 45-54, and 55-65 years. The repeatability coefficient was assessed by twice measuring 39 diabetic patients without known neuropathy. Warm thermal threshold in the hand showed a significant increase with age from 0.09 +/- 0.5 (mean +/- SD) in the youngest age group to 0.17 +/- 0.08 degree C (p less than 0.05) in the oldest age group. Cold thermal threshold in the hand (varying between 0.08 +/- 0.04 and 0.14 +/- 0.05 degree C) and warm thermal threshold in the foot (varying between 2.45 +/- 1.93 and 4.06 +/- 2.57 degrees C) did not differ significantly between the four age groups. There was a significant increase in cold thermal threshold in the foot with age, increasing from 0.31 +/- 0.24 to 0.56 +/- 0.44 degree C (p less than 0.05). Reproducibility in the diabetic subjects was good for measurements of warm and cold threshold in the hand, but poor for warm threshold in the foot in the normal range and for cold thermal threshold in the abnormal range.

Influence of caffeine, sweating and local hyperemisation on "Marstock" thermotesting

Marstock thermotesting evaluates A-delta- and C-fiber functions. To optimize this method, intraindividual variations of vasodilatation, blood flow and sympathetic activity probably biasing thermotest results were imitated by exogenous stimuli which strongly exaggerated these intraindividual variations. In 20 healthy subjects, warm (WT), cold (CT), and heat-pain (HT) thresholds were determined in the morning at the thenar (th), the volar wrist (wr), and behind the malleolus internus (mi). Thresholds at the thenar and the volar wrist were compared with those during severe sweating induced by Minor's test, and to those measured when sympathetic activity had been increased by the ingestion of a high dose of caffeine (0.5 g). Furthermore, the intraindividual variation of local capillary blood flow and vasodilatation was imitated by a rubefacient liniment (Forapin) applied to the three sites. After a local hyperemisation had been induced thermal thresholds were measured and compared to those measured without any stimulation. Local hyperemia did not influence thermal thresholds significantly. Sweating only lowered cold thresholds at the thenar significantly and only slightly raised warm and heat-pain thresholds at the thenar. Caffeine significantly lowered warm thresholds and raised heat-pain thresholds at the thenar. To conclude, the tested exogenous interferences do not disturb thermal perception markedly, especially when testing is not performed at the thenar, but at the volar wrist and when the testing-procedure and parameters are standardised.

Vibratory and thermal thresholds in diabetics with and without clinical neuropathy

Vibration and thermal detection threshold and heat pain threshold were determined in 34 diabetics scrutinized for clinical neuropathy using a standardized questionnaire and examination form. On the basis of the clinical grading patients were classified as having either no neuropathy or a neuropathy of increasing severity. As expected thermal and vibratory detection threshold increased with increasing severity of neuropathy. Comparison between diabetics without symptoms and signs of neuropathy and a corresponding non-diabetic control group showed that a warm sensibility index (WSI = the range in which non-noxious heat is perceived) was significantly lower on feet in diabetics than in their matched non-diabetic controls. The findings show that quantitative assessment of thermal sensitivity may be of value to detect early small nerve fiber dysfunction even in patients without symptoms or signs of a clinical neuropathy.

Assessment of basal and stimulated sweating in diabetes using a direct-reading computerized sudorometer

Abnormalities of eccrine sweating are thought to be common in diabetes. We describe a ventilated-capsule sudorometer for the continuous measurement of basal and stimulated sweat secretion. It is sensitive (detecting as little as 200 ng water vapour), precise, and stable. Since it measures dewpoint rather than relative humidity, it can be calibrated to read sweat volumes directly and independently of ambient temperature and humidity. Preliminary studies using this technique show that basal skin water loss is significantly diminished in patients with established diabetic neuropathy (0.91 +/- 0.18 g (+/- SD) cm-2 h-1) compared with normal subjects (1.21 +/- 0.39 g cm-2 h-1; p = 0.04) and non-neuropathic diabetic subjects (1.32 +/- 0.48 g cm-2 h-1; p = 0.04), and that local sweating induced by iontophoresis of 10 g l-1 acetylcholine is significantly reduced in diabetic subjects up to 5 min of recording (0.95 +/- 0.43 vs 1.26 +/- 0.40 mg; p = 0.02). In neuropathic subjects both low- and high-amplitude responses are seen, the latter probably representing denervation supersensitivity. Further studies with sensitive sudorometry should enable the mechanisms of these abnormal responses to be established.

Peripheral neuropathy profile in various groups of diabetics

The results of applying a battery of peripheral nerve function tests in three groups of diabetics are reported. The tests examined the integrity of all the major subgroups of nerve fibres. The diabetics were grouped according to the clinical severity of their neuropathy: Group I--11 patients with long standing diabetes but clinically insignificant neuropathy, Group II--27 patients with mild neuropathy and Group III--23 patients with neuropathic foot lesions. As expected the incidence of abnormality of all functions increased from Group I to III, but within a group there was no clear pattern of differential involvement of different fibre types. The study has identified those tests that are suitable for detecting early neuropathy (warming and vibration perception thresholds and sensory nerve action potentials) and those which are likely to be useful in assessing deterioration or improvement (particularly vibration perception threshold), but since the different tests cannot be equally matched for sensitivity it is not possible to interpret the results in terms of the degree of pathological involvement of different fibre groups.

Endogenous levels of nerve growth factor (NGF) are altered in experimental diabetes mellitus: a possible role for NGF in the pathogenesis of diabetic neuropathy

Sympathetic and neural-crest derived sensory neurons consisting of unmyelinated and small myelinated fibers are known to be affected at an early stage in diabetes mellitus (DM). Since these peripheral neurons need nerve growth factor (NGF) for their development and maintenance of function in adulthood, changes in endogenous NGF levels could be of relevance for the pathogenesis of diabetic neuropathy (DNP). Using an improved two-site enzyme immunoassay for NGF, we have investigated whether endogenous NGF levels are altered in Sprague-Dawley rats with DM induced by a single injection of streptozotocin (STZ). STZ-treated rats are known to develop in many respects equivalents to neuropathic complications observed in human DM. We found in some sympathetically innervated target organs decreased NGF contents by maximally 56%: transiently in the iris 2 weeks and in the ventricle 12-24 weeks after DM induction and permanently in the submandibular gland already 3 days after DM induction. Several weeks after onset of DM, NGF content was increased by maximally 145-300% in most peripheral targets investigated, such as in iris, cardiac atrium and ventricle, spleen, prostate gland, and vas deferens. This is suggestive for an impaired NGF removal by NGF-sensitive neurons in diabetic rats. Moreover, NGF levels were decreased to minimally 42.6 +/- 4% of control in the NGF-transporting sciatic nerve. NGF levels began to decrease not before 3 weeks after DM induction and remained decreased with 54.0 +/- 5% of control even after 6 months duration of DM. About the same time (i.e., 2 weeks after induction of DM) NGF levels began to decrease in the superior cervical ganglion (where the sympathetic perikarya are located) to minimally 53.2 +/- 4% of control 12 weeks after DM induction. No altered NGF levels were observed during a 3-month duration of DM in the terminal ileum and sensory trigeminal ganglion. Since NGF exerts its neurotrophic action in the perikarya after its retrograde transport from the NGF-producing periphery, our results are consistent with the hypothesis that an alteration in NGF levels may play a role in the pathogenesis of DNP as far as sympathetic neurons are concerned. Thus, our results suggest that DM influences the production and/or transport of endogenous NGF and consequently, that a deprivation of this neurotrophic factor may account for some of the functional deficits known to occur in DNP, such as impaired catecholaminergic transmitter synthesis. This hypothesis possibly opens the way for new concepts in the therapy of DNP.

Quantitative noninvasive electrophysiological evaluation of the activity of the cutaneous division of the sympathetic nervous system

The functional status of the cutaneous division of the orthosympathetic nervous system was indirectly and non-invasively assessed by monitoring the skin electrical relative resistance variations (SERV). The advantages of our recording system of second generation were (1) simultaneous recording on two or four channels of the evoked electrodermal response to psychic or to sensorial stimulus; (2) self-balancing system which allows the recording of the relative variation of the electric parameter, i.e. its variation with time; (3) precise determination of the amplitude (omega/s, mu F/s) of the evoked response; (4) reference of the latency time (LT) of the evoked response to the length of the anatomical pathway of the signal giving the autonomic conduction velocity (ACV). Decrease in diabetic autonomic neuropathy of both spontaneous and evoked electrodermal activities suggested their relationship with cutaneous sympathetic activity.

A comparison of two methods for measuring thermal thresholds in diabetic neuropathy

Thermal thresholds can be measured psychophysically using either the method of limits or a forced-choice method. We have compared the two methods in 367 diabetic patients, 128 with symptomatic neuropathy. The Sensortek method was chosen for the forced-choice device, the Somedic modification of the Marstock method for a method of limits. Cooling and heat pain thresholds were also measured using the Marstock method. Somedic thermal thresholds increase with age in normal subjects, but not to a clinically significant degree. In diabetics Marstock warm threshold increased by 0.8 degrees C/decade, Sensortek by 0.1 degrees C/decade. Both methods had a high coefficient of variation in normal subjects (Sensortek 29%, Marstock warm 14%, cool 42%). The prevalence of abnormal thresholds was similar for both methods (28-32%), though Marstock heat pain thresholds were less frequently abnormal (18%). Only 15-18% of patients had abnormal results in both tests. Sensortek thresholds were significantly lower on repeat testing, and all thresholds were higher in symptomatic patients. Both methods are suitable for clinical thermal testing, though the method of limits is quicker. In screening studies the choice of a suitable apparatus need not be determined by the psychophysical basis of the test.

Depletion of cutaneous nerves and neuropeptides in diabetes mellitus: an immunocytochemical study

Immunocytochemistry for the general neuronal marker protein gene product 9.5 and four neuropeptides (calcitonin gene-related peptide, substance P, vasoactive intestinal polypeptide and neuropeptide Y) was performed on 20 skin biopsy specimens from 19 diabetic patients, age range 20-75 years, 17 Type 2 (non-insulin-dependent) and 3 Type 1 (insulin-dependent). Fifteen specimens were from the lower limb, 3 from the upper limb and 2 from the abdominal wall. Seven subjects had lower limb neurophysiological tests. All but one specimen showed reduced protein gene product 9.5 and neuropeptide immunoreactivity. Reduced protein gene product 9.5 and neuropeptide immunoreactivity was found in specimens taken from the abdominal wall and hand as well as those from the leg, and also in specimens from patients undergoing amputation for peripheral vascular disease. In general, the greater the number of abnormal neurophysiological tests, the greater the extent of neuronal abnormalities. Three patients with normal tests had abnormalities of dermal innervation. While these changes are also found in other axonal neuropathies, in the absence of other causes of peripheral nerve disease and of macrovascular disease, immunocytochemistry of skin biopsies may have a role in the assessment of diabetic neuropathy and its response to treatment.

Evaluation of thermal, pain, and vibration sensation thresholds in newly diagnosed type 1 diabetic patients

Small and large fibre function was studied in 40 non-ketotic, newly diagnosed Type 1 diabetic patients and 48 age-matched controls, using 12 quantitative tests for assessment of cutaneous sensation. Patients were aged 10-39 years and had been treated with insulin for 4-31 days. Thermal discrimination (foot), warm and cold thermal perception (thenar eminence and foot), and heat and cold pain perception thresholds (thenar eminence) were significantly elevated in the patients as compared with the controls (p less than 0.05 to p less than 0.001). No significant differences in thermal discrimination (thenar), heat and cold pain perception (foot), and metacarpal as well as malleolar vibration perception thresholds were noted between the groups. The rates of abnormalities among the individual tests ranged from 0% to 27.5%, being lowest for vibration perception and highest for thermal perception thresholds after cold stimuli. The results in nine of 12 tests correlated significantly with age, but only two were related to HbA1c. Thus, sensory neural functions transmitted by small fibres, but not those transmitted by large fibres, were impaired in newly diagnosed Type 1 diabetics after the correction of initial ketosis and hyperglycaemia. Cooling perception tests were most sensitive in detecting abnormality. An age-related involvement of different small fibre functions was present in these patients.

Pelvic floor neuropathy: a comparative study of diabetes mellitus and idiopathic faecal incontinence

Twenty one patients with diabetic peripheral neuropathy, 18 with idiopathic faecal incontinence and 11 normal controls were studied with techniques of mucosal electrosensitivity, rectal distension for the quantitative assessment of anorectal sensation, and manometric and electromyographic tests for the assessment of anorectal motor function. An asymptomatic sensorimotor deficit was found in the anal canal of patients with diabetic peripheral neuropathy. Mucosal electrosensitivity thresholds in the anal canal were significantly higher (p less than 0.01 v controls) and fibre density of the external anal sphincter significantly raised (p less than 0.0001 v controls). Anal manometry and pudendal nerve terminal motor latencies were similar to controls. In patients with idiopathic faecal incontinence the tests of sensory and motor function also showed a sensorimotor neuropathy; compared with controls, mucosal electrosensitivity thresholds were significantly higher (p less than 0.002), anal canal resting and maximum squeeze pressures were significantly lower (p less than 0.05 and p less than 0.002 respectively), and pudendal nerve terminal motor latencies and fibre density of the external anal sphincter were significantly raised (both p less than 0.05). Sensory thresholds to rectal distension were similar in all groups. Pelvic floor sensorimotor neuropathy in diabetic patients has several features in common with that of patients with idiopathic faecal incontinence but its functional significance remains uncertain.