A prospective study of sensory function in patients with type 2 diabetes

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.

Reproducibility of peroneal motor nerve conduction measurement in older adults

OBJECTIVE

While neuropathy is common in the elderly, nerve conduction (NC) reproducibility in older adults is not well-established. We sought to evaluate intraobserver reproducibility of peroneal motor NC measures in a diverse sample of older adults.

METHODS

We measured peroneal motor NC amplitude and velocity in a subset of participants (mean age=82.9±2.7, n=62, 50% female, 51.6% black, 35.5% DM) in the Health, Aging, and Body Composition Study. Using coefficients of variation (CVs), intraclass correlation coefficients (ICCs), and Bland Altman Plots, we compared two sets of measurements taken by the same examiner hours apart on the same day.

RESULTS

Low CVs (2.15-4.24%) and moderate to high ICCs (0.75-0.99) were observed. No systematic variation was found across measures. Despite small numbers in some subgroups, we found no differences in reproducibility by diabetes, race or study site.

CONCLUSION

NC measures have moderate to high intraobsever reproducibility in older adults and are not affected by diabetes, race, or gender.

SIGNIFICANCE

These data provide evidence to support use of these measures in aging research.

The natural history of chronic painful peripheral neuropathy in a community diabetes population

AIMS

To examine the natural history of chronic painful diabetic neuropathy (CPDN).

METHODS

A cross-sectional study of 350 people with diabetes was performed during 1998-1999 to assess the prevalence of CPDN in the community. Fifty-six patients with CPDN were identified and were followed up an average of 5 years later.

RESULTS

From the original cohort, 12 patients had died and 14 had moved away or were unable to participate in the follow-up study. Thus 30 patients with CPDN [21 male, mean (SD) age 68.6 years (9.4), mean (SD) duration of diabetes 15.4 years (8.7)] were re-assessed. Seven (23%) had been pain free for at least 12 months and 23 continued to report neuropathic pain of similar quality and severity [total McGill Pain Questionnaire Score median (interquartile range) at follow-up 22 (16-39) vs. 20 (16-33) at baseline, P = 0.3; mean (SD) visual analogue scale (VAS) score for pain over the preceding 24 h 5.3 cm (2.9) vs. 4.6 cm (2.5) at baseline, P = 0.1]. Only 65% had ever received treatment for CPDN despite 96% (22/23) reporting pain to their physician; 43.5% had received antidepressants, 17.4% anticonvulsants, 39% opiates and 30% had tried complementary therapies.

CONCLUSIONS

The neuropathic pain of CPDN can resolve completely over time in a minority (23%). In those in whom painful neuropathic symptoms had persisted over 5 years, no significant improvement in pain intensity was observed. Despite the improvement in treatment modalities for chronic pain in recent years, patients with CPDN continue to be inadequately treated.

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.

Hyperosmolar Solutions Selectively Block Action Potentials in Rat Myelinated Sensory Fibers: Implications for Diabetic Neuropathy

Diabetic neuropathy is a common complication of diabetes mellitus patients. It is a wide range of abnormalities affecting proximal and distal peripheral sensory and motor nerves. Although plasma hyperosmolality is a common finding in diabetes mellitus, the effects of hyperosmolality on conduction of various sensory signal components have not been addressed in detail. Here we show that in rat dorsal root ganglion (DRG) preparations from normal rats, hyperosmolar solutions (360 mmol/kg, containing increased glucose, sucrose, NaCl, or mannitol) produce a selective block of signal propagation in myelinated sensory A-fibers. In compound action potential (CAP) recordings with suction electrodes, peak A-fiber CAP amplitude was selectively decreased (20%), while the C-fiber peak remained intact or was slightly increased. Hyperosmolar solutions had smaller effects on conduction velocity (CV) of both A- and C-fibers (approximately 5% decrease). Hyperosmolality-induced CAP changes could not be observed during recordings from isolated spinal nerves but were evident during recordings from desheathed spinal nerves. In intracellular recordings, hyperosmolar solutions produced a block of spinal nerve-evoked action potential invasion into the somata of some A-fiber neurons. Removal of extracellular calcium completely prevented the hyperosmolality-induced CAP decreases. Based on these data, we propose that the decreased CAP amplitudes recorded in human patients and in animal models of diabetes are in part due to the effects of hyperosmolality and would depend on the extracellular osmolality at the time of sensory testing. We also hypothesize that hyperosmolality may contribute to both the sensory abnormalities (paresthesias) and the chronic pain symptoms of diabetic neuropathy.

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.

Noise-enhanced vibrotactile sensitivity in older adults, patients with stroke, and patients with diabetic neuropathy

OBJECTIVE

To test the hypothesis that vibrotactile detection thresholds in older adults, patients with stroke, and patients with diabetic neuropathy can be significantly reduced with the introduction of mechanical noise.

DESIGN

A randomized controlled study.

SETTING

A university research laboratory.

PARTICIPANTS

Twelve healthy elderly subjects (age range, 67-85y), 5 patients with stroke (age range, 24-64y), and 8 patients with diabetic neuropathy (age range, 53-77y).

INTERVENTIONS

Each subject's detection thresholds (ie, minimum level of stimulus to be detected) for a vibrotactile stimulus without and with mechanical noise (ie, random vibration with a small intensity) were determined by using a 4-, 2-, and 1-stepping algorithm. The stimuli were applied to the fingertip and/or to the first metatarsal of the foot.

MAIN OUTCOME MEASURE

Detection threshold for a vibrotactile stimulus.

RESULTS

The detection threshold at the fingertip for the vibration stimulus with mechanical noise was significantly lower than that without mechanical noise for all 12 elderly subjects, for 4 of the 5 patients with stroke, and all 8 patients with diabetic neuropathy. For the 8 patients with diabetes, mechanical noise also significantly reduced the vibrotactile detection threshold at the foot.

CONCLUSIONS

Reduced vibrotactile sensitivity in older adults, patients with stroke, and patients with diabetic neuropathy can be significantly improved with input mechanical noise. Noise-based techniques and devices may prove useful in overcoming age- and disease-related losses in sensorimotor function.

Risk factors for diabetic neuropathy and foot ulceration

Peripheral sensory neuropathy (PSN) and foot ulcers are disabling and expensive complications of diabetes with few therapeutic options. Knowledge of risk factors for both complications, based on prospective observational studies, permits identification of individuals at high risk and provides options for intervention. Glycemia is the main modifiable risk factor for PSN, whereas PSN and trauma are the principal potentially modifiable risk factors for the development of foot ulceration.

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.