Asymptomatic small fiber neuropathy in diabetes mellitus: investigations with intraepidermal nerve fiber density, quantitative sensory testing and laser-evoked potentials. J Neurol. 2011;258:1852-1864. [PMID: 21472496 DOI: 10.1007/s00415-011-6031-z]

[Diabetic neuropathy: do not only consider distal symmetrical neuropathy]

BACKGROUND

Diabetic neuropathy is a common complication of diabetes mellitus. The length-dependent symmetrical sensorimotor type of neuropathy is the most prevalent form of diabetic neuropathy but other forms of diabetic neuropathy also need to be kept in mind. Their differential diagnosis is often more challenging but implicates specific forms of treatment other than improvement of metabolic control.

AIM OF THE STUDY

This article gives an overview of the less frequent forms of diabetic neuropathy and discusses their impact, diagnostic and therapeutic implications.

RESULTS

Autonomic diabetic neuropathy, diabetic small fiber neuropathy and less frequent forms of diabetic neuropathy, such as diabetic radiculoplexopathy, diabetic neuropathy of cranial nerves, therapy-induced neuropathy and alternative causes of peripheral neuropathy in patients with diabetes are described.

DISCUSSION

Diagnosis of less frequent subtypes of diabetic neuropathy and differentiation towards alternative causes of peripheral neuropathy are often difficult in daily medical routine. Diagnostic clues are helpful in identifying rarer forms of diabetic neuropathy, thus enabling more specific treatment.

Association between visceral, cardiac and sensorimotor polyneuropathies in diabetes mellitus

AIMS

Gastrointestinal complaints are common in diabetes mellitus. However, its association to peripheral sensorimotor and autonomic neuropathies is not well investigated. The aim was to assess skin, muscle, bone and visceral sensitivity in diabetes patients with sensorimotor neuropathy, and correlate these with gastrointestinal symptoms and degree of cardiac autonomic neuropathy.

METHODS

Twenty patients with sensorimotor neuropathy (65% type 2 diabetes, aged 58.3±12.0 years, diabetes duration 15.8±10.0 years) and 16 healthy controls were recruited. Cutaneous sensitivity to von Frey filaments, mechanical allodynia, muscle/bone/rectosigmoid sensitivities, and heart rate variability were examined. Gastrointestinal symptom scores (PAGI-SYM) and health-related quality of life (SF-36) were also recorded.

RESULTS

Patients displayed hypesthesia to von Frey filaments (p=0.028), but no difference to muscle and bone pain sensitivities. Also, patients were hyposensitive to multimodal rectal stimulations (all p<0.05), although they suffered more gastrointestinal complaints. Heart rate variability was reduced in the patient cohort. Rectal mechanical and cutaneous sensitivities correlated (p<0.001), and both were associated with heart rate variability as well as PAGI-SYM and SF-36 scores (p<0.01).

CONCLUSIONS

In diabetic sensorimotor neuropathy there is substantial evidence of concomitant cutaneous, cardiac and visceral autonomic neuropathies. The neuropathy may reduce quality of life and explain the higher prevalence of gastrointestinal complaints.

Renal nerve ultrastructural alterations in short term and long term experimental diabetes

BACKGROUND

Despite the evidence that renal hemodynamics is impaired in experimental diabetes, associated with glomeruli structural alterations, renal nerves were not yet investigated in experimental models of diabetes and the contribution of nerve alterations to the diabetic nephropathy remains to be investigated. We aimed to determine if ultrastructural morphometric parameters of the renal nerves are affected by short term and/or long term experimental diabetes and if insulin treatment reverses these alterations. Left renal nerves were evaluated 15 days or 12 weeks (N = 10 in each group) after induction of diabetes, with a single injection of streptozotocin (STZ). Control rats (N = 10 in each group) were injected with vehicle (citrate buffer). Treated animals (N = 10 in each group) received a single subcutaneous injection of insulin on a daily basis. Arterial pressure, together with the renal nerves activity, was recorded 15 days (short-term) or 12 weeks (long-term) after STZ injection. After the recordings, the renal nerves were dissected, prepared for light and transmission electron microscopy, and fascicle and fibers morphometry were carried out with computer software.

RESULTS

The major diabetic alteration on the renal nerves was a small myelinated fibers loss since their number was smaller on chronic diabetic animals, the average morphometric parameters of the myelinated fibers were larger on chronic diabetic animals and distribution histograms of fiber diameter was significantly shifted to the right on chronic diabetic animals. These alterations began early, after 15 days of diabetes induction, associated with a severe mitochondrial damage, and were not prevented by conventional insulin treatment.

CONCLUSIONS

The experimental diabetes, induced by a single intravenous injection of STZ, in adult male Wistar rats, caused small fiber loss in the renal nerves, probably due to the early mitochondrial damage. Conventional treatment with insulin was able to correct the weight gain and metabolic changes in diabetic animals, without, however, correcting and / or preventing damage to the thin fibers caused by STZ-induced diabetes. The kidney innervation is impaired in this diabetic model suggesting that alterations of the renal nerves may play a role in the development of the diabetic nephropathy.

Structural and functional small fiber abnormalities in the neuropathic postural tachycardia syndrome

OBJECTIVE

To define the neuropathology, clinical phenotype, autonomic physiology and differentiating features in individuals with neuropathic and non-neuropathic postural tachycardia syndrome (POTS).

METHODS

Twenty-four subjects with POTS and 10 healthy control subjects had skin biopsy analysis of intra-epidermal nerve fiber density (IENFD), quantitative sensory testing (QST) and autonomic testing. Subjects completed quality of life, fatigue and disability questionnaires. Subjects were divided into neuropathic and non-neuropathic POTS, defined by abnormal IENFD and abnormal small fiber and sudomotor function.

RESULTS

Nine of 24 subjects had neuropathic POTS and had significantly lower resting and tilted heart rates; reduced parasympathetic function; and lower phase 4 valsalva maneuver overshoot compared with those with non-neuropathic POTS (P<0.05). Neuropathic POTS subjects also had less anxiety and depression and greater overall self-perceived health-related quality of life scores than non-neuropathic POTS subjects. A sub-group of POTS patients (cholinergic POTS) had abnormal proximal sudomotor function and symptoms that suggest gastrointestinal and genitourinary parasympathetic nervous system dysfunction.

CONCLUSIONS AND RELEVANCE

POTS subtypes may be distinguished using small fiber and autonomic structural and functional criteria. Patients with non-neuropathic POTS have greater anxiety, greater depression and lower health-related quality of life scores compared to those with neuropathic POTS. These findings suggest different pathophysiological processes underlie the postural tachycardia in neuropathic and non-neuropathic POTS patients. The findings have implications for the therapeutic interventions to treat this disorder.

Sjögren Syndrome-Associated Small Fiber Neuropathy: Characterization From a Prospective Series of 40 Cases

We conducted the current study to analyze the clinical, immunologic, and neurophysiologic features of primary Sjögren syndrome (pSS)-associated sensory small fiber neuropathies (SFNs). Forty consecutive pSS patients with SFN were included. SFN was defined by the presence of suggestive sensory painful symptoms with normal nerve conduction studies and abnormal neurophysiologic tests for small nerve fibers or a low intraepidermal nerve fiber density at skin biopsy. Included patients were compared to 100 pSS patients without peripheral neuropathy.SFN patients were mainly female (92.5%). Age at pSS diagnosis was 55.3 ± 13.1 years, and at SFN diagnosis, 58.9 ± 11.8 years, with a median time to SFN diagnosis after symptom onset of 3.4 years. Clinical symptoms included burning pains (90%), numbness (87.5%), tingling (82.5%), pins and needles (72.5%), electric discharges (70%), and allodynia (55%). Dysautonomia included vasomotor symptoms (66%) and hyperhidrosis (47%). Abnormal neurophysiologic tests included laser evoked potentials (97.5%), thermal quantitative sensory testing (67.5%), and sympathetic skin reflex (40%). A skin biopsy revealed low intraepidermal nerve fiber density in 76% of the 17 tested patients.Compared to the 100 pSS patients without peripheral neuropathy, the 40 pSS-SFN patients were older at pSS diagnosis (55.3 ± 13.1 vs. 49.5 ± 14.9 yr; p = 0.03), and more often had xerostomia (97.5% vs. 81%; p = 0.01) and arthralgia (82.5% vs. 65.0%; p = 0.04). Immunologically, they were characterized by a lower prevalence of serum B-cell activation markers, that is, antinuclear antibodies (65% vs. 85%; p = 0.01), anti-SSA (42.5% vs. 71%; p = 0.002), and anti-SSB (17.5% vs. 39%; p = 0.017); rheumatoid factor (32.5% vs. 66%; p = 0.0005); and hypergammaglobulinemia (35% vs. 62%; p = 0.005).In conclusion, we report the main features of SFN in patients with pSS, the first such study to our knowledge. Our results show that patients with pSS-associated SFN are characterized by an older age at pSS diagnosis and a distinctive immunologic profile hallmarked by a lower frequency of serum B-cell activation markers.

Mechanisms and management of diabetic painful distal symmetrical polyneuropathy

Although a number of the diabetic neuropathies may result in painful symptomatology, this review focuses on the most common: chronic sensorimotor distal symmetrical polyneuropathy (DSPN). It is estimated that 15-20% of diabetic patients may have painful DSPN, but not all of these will require therapy. In practice, the diagnosis of DSPN is a clinical one, whereas for longitudinal studies and clinical trials, quantitative sensory testing and electrophysiological assessment are usually necessary. A number of simple numeric rating scales are available to assess the frequency and severity of neuropathic pain. Although the exact pathophysiological processes that result in diabetic neuropathic pain remain enigmatic, both peripheral and central mechanisms have been implicated, and extend from altered channel function in peripheral nerve through enhanced spinal processing and changes in many higher centers. A number of pharmacological agents have proven efficacy in painful DSPN, but all are prone to side effects, and none impact the underlying pathophysiological abnormalities because they are only symptomatic therapy. The two first-line therapies approved by regulatory authorities for painful neuropathy are duloxetine and pregabalin. α-Lipoic acid, an antioxidant and pathogenic therapy, has evidence of efficacy but is not licensed in the U.S. and several European countries. All patients with DSPN are at increased risk of foot ulceration and require foot care, education, and if possible, regular podiatry assessment.

Painful and painless diabetic neuropathy: one disease or two?

Painful diabetic polyneuropathy (PDPN) is generally considered a variant of diabetic polyneuropathy (DPN) but the identification of distinctive aspects that characterize painful compared with painless DPN has however been addressed in many studies, mainly with the purpose of better understanding the mechanisms of neuropathic pain in the scenario of peripheral nerve damage of DPN, of determining risk markers for pain development, and also of recognizing who might respond to treatments. This review is aimed at examining available literature dealing with the issue of similarities and differences between painful and painless DPN in an attempt to respond to the question of whether painful and painless DPN are the same disease or not and to address the conundrum of why some people develop the insensate variety of DPN whilst others experience distressing pain. Thus, from the perspective of comparing painful with painless forms of DPN, this review considers the clinical correlates of PDPN, its distinctive framework of symptoms, signs, and nerve functional and structural abnormalities, the question of large and small fiber involvement, the peripheral pain mechanisms, the central processing of pain and some new insights into the pathogenesis of pain in peripheral polyneuropathies and PDPN.

Mechanism- and experience-based strategies to optimize treatment response to the capsaicin 8% cutaneous patch in patients with localized neuropathic pain

The capsaicin 8% cutaneous patch is an emergent new treatment option for patients with peripheral neuropathic pain. In randomized controlled clinical studies relevant pain relief for 12 weeks was achieved in about one third of patients following a single application. The first part of this paper is a review of the pathophysiology, pharmacology, and published clinical trials with the capsaicin 8% cutaneous patch. The second part reports on outcomes of an interdisciplinary expert workshop, where new treatment results of three major German pain centers were presented and reviewed with the objectives of obtaining responder rates for different pain syndromes, assessing maintenance of effect under real-life conditions, and giving recommendations for practical care. The 12 week responder rates with pain relief of ≥ 30% were comparable in patients with mononeuropathies (37.9%) and postherpetic neuralgia (38.8%). Similar responder rates were seen in a subgroup of patients with cervical spine radiculopathy and back pain (46.7%). In HIV-associated neuropathy the responder rates were high (47.8%) but lower in patients with other polyneuropathies (17.6%). Response rates were nearly identical after 1 week (46.6%) and 4 weeks (43.3) and dropped only slightly at 12 weeks (37.4%). In a subgroup of 54 patients who underwent a second treatment, efficacy was maintained. Response rates in patients with or without lidocaine pretreatment were comparable. Treatment with the capsaicin 8% cutaneous patch was generally safe and well tolerated. The workshop panel recommended further investigation of opportunities to improve the application procedure and to perform studies on the skin penetration and distribution of capsaicin. A modified quantitative sensory testing (QST) should be developed for clinical practice in order to better understand the correlation of sensory profiles and response to capsaicin treatment.

Can ultrasound of the tibial nerve detect diabetic peripheral neuropathy? A cross-sectional study

OBJECTIVE

Peripheral nerve imaging by portable ultrasound (US) may serve as a noninvasive and lower-cost alternative to nerve conduction studies (NCS) for diagnosis and staging of diabetic sensorimotor polyneuropathy (DSP). We aimed to examine the association between the size of the posterior tibial nerve (PTN) and the presence and severity of DSP.

RESEARCH DESIGN AND METHODS

We performed a cross-sectional study of 98 consecutive diabetic patients classified by NCS as subjects with DSP or control subjects. Severity was determined using the Toronto Clinical Neuropathy Score. A masked expert sonographer measured the cross-sectional area (CSA) of the PTN at 1, 3, and 5 cm proximal to the medial malleolus.

RESULTS

Fifty-five patients had DSP. The mean CSA of the PTN in DSP compared with control subjects at distances of 1 (23.03 vs. 17.72 mm(2); P = 0.004), 3 (22.59 vs. 17.69 mm(2); P < 0.0001), and 5 cm (22.05 vs. 17.25 mm(2); P = 0.0005) proximal to the medial malleolus was significantly larger. Although the area under the curve (AUC) for CSA measurements at all three anatomical levels was similar, the CSA measured at 3 cm above the medial malleolus had an optimal threshold value for identification of DSP (19.01 mm(2)) with a sensitivity of 0.69 and a specificity of 0.77 by AUC analysis.

CONCLUSIONS

This large study of diabetic patients confirms that the CSA of the PTN is larger in patients with DSP than in control subjects, and US is a promising point-of-care screening tool for DSP.

Evaluation of proxy tests for SFSN: evidence for mixed small and large fiber dysfunction

Background

Though intra-epidermal nerve fiber density (IENFD) is considered the gold standard for diagnosis of small fiber sensory neuropathy (SFSN), we aimed to determine if novel threshold values derived from standard tests of small or large fiber function could serve as diagnostic alternatives.

Methods

Seventy-four consecutive patients with painful polyneuropathy and normal nerve conduction studies (NCS) were defined as SFSN cases or controls by distal IENFD <5.4 and ≥5.4 fibers/mm, respectively. Diagnostic performance of small fiber [cooling (CDT) and heat perception (HP) thresholds, axon reflex-mediated neurogenic vasodilatation] and large fiber function tests [vibration perception thresholds (VPT) and sural nerve conduction parameters] were determined by receiver operating-characteristic (ROC) curve analyses.

Results

The 26(35%) SFSN cases had mean IENFD 3.3±1.7 fibers/mm and the 48(65%) controls 9.9±2.9 fibers/mm. Male gender (p = 0.02) and older age (p = 0.02) were associated with SFSN cases compared to controls. VPT were higher and CDT lower in SFSN cases, but the largest magnitude of differences was observed for sural nerve amplitude. It had the greatest area under the ROC curve (0.75) compared to all other tests (p<0.001 for all comparisons) and the optimal threshold value of ≤12 µV defined SFSN cases with 80% sensitivity and 72% specificity.

Conclusion

In patients presenting with polyneuropathy manifestations and normal NCS, though small fiber function tests were intuitively considered the best alternative measures to predict reduced IENFD, their diagnostic performance was poor. Instead, novel threshold values within the normal range for large fiber tests should be considered as an alternative strategy to select subjects for skin biopsy in diagnostic protocols for SFSN.

Neuropathic pain: is quantitative sensory testing helpful?

Neuropathic pain arises as a consequence of a lesion or disease affecting the somatosensory system and is characterised by a combination of positive and negative sensory symptoms. Quantitative sensory testing (QST) examines the sensory perception after application of different mechanical and thermal stimuli of controlled intensity and the function of both large (A-beta) and small (A-delta and C) nerve fibres, including the corresponding central pathways. QST can be used to determine detection, pain thresholds and stimulus-response curves and can thus detect both negative and positive sensory signs, the second ones not being assessed by other methods. Similarly to all other psychophysical tests QST requires standardised examination, instructions and data evaluation to receive valid and reliable results. Since normative data are available, QST can contribute also to the individual diagnosis of neuropathy, especially in the case of isolated small-fibre neuropathy, in contrast to the conventional electrophysiology which assesses only large myelinated fibres. For example, detection of early stages of subclinical neuropathy in symptomatic or asymptomatic patients with diabetes mellitus can be helpful to optimise treatment and identify diabetic foot at risk of ulceration. QST assessed the individual's sensory profile and thus can be valuable to evaluate the underlying pain mechanisms which occur in different frequencies even in the same neuropathic pain syndromes. Furthermore, assessing the exact sensory phenotype by QST might be useful in the future to identify responders to certain treatments in accordance to the underlying pain mechanisms.

Laser heat stimulation of tiny skin areas adds valuable information to quantitative sensory testing in postherpetic neuralgia

Patients suffering from postherpetic neuralgia often complain about hypo- or hypersensation in the affected dermatome. The loss of thermal sensitivity has been demonstrated by quantitative sensory testing as being associated with small-fiber (Aδ- and C-fiber) deafferentation. We aimed to compare laser stimulation (radiant heat) to thermode stimulation (contact heat) with regard to their sensitivity and specificity to detect thermal sensory deficits related to small-fiber dysfunction in postherpetic neuralgia. We contrasted detection rate of laser stimuli with 5 thermal parameters (thresholds of cold/warm detection, cold/heat pain, and sensory limen) of quantitative sensory testing. Sixteen patients diagnosed with unilateral postherpetic neuralgia and 16 age- and gender-matched healthy control subjects were tested. Quantitative sensory testing and laser stimulation of tiny skin areas were performed in the neuralgia-affected skin and in the contralateral homologue of the neuralgia-free body side. Across the 5 thermal parameters of thermode stimulation, only one parameter (warm detection threshold) revealed sensory abnormalities (thermal hypoesthesia to warm stimuli) in the neuralgia-affected skin area of patients but not in the contralateral area, as compared to the control group. In contrast, patients perceived significantly less laser stimuli both in the affected skin and in the contralateral skin compared to controls. Overall, laser stimulation proved more sensitive and specific in detecting thermal sensory abnormalities in the neuralgia-affected skin, as well as in the control skin, than any single thermal parameter of thermode stimulation. Thus, laser stimulation of tiny skin areas might be a useful diagnostic tool for small-fiber dysfunction.