Sonographic assessment of nerve blood flow in diabetic neuropathy.

AIMS: To undertake sonographic assessment of nerve blood flow in people with Type 2 diabetes and correlate the findings with neuropathy severity scores and electrophysiological measurements. METHODS: Median and tibial nerve ultrasound scans were undertaken in 75 people with diabetes and 30 aged-matched controls without diabetes, using a high-resolution linear probe at non-entrapment sites. Nerve blood flow was quantified using power Doppler techniques to obtain the vessel score and the maximum perfusion intensity. Neuropathy severity was assessed using a total neuropathy score. RESULTS: Diabetic nerves had higher rates of nerve blood flow detection (28%) compared to the control group (P < 0.0001). Significant correlations were found between nerve blood flow measurements and nerve size (P <0.001), reported sensory symptoms (P < 0.05) and neuropathy severity scores (P < 0.001). The cohort with diabetes had significantly larger median (8.5 ± 0.3 mm2 vs 7.2 ± 0.1 mm2 ; P < 0.05) and tibial nerves (18.0 ± 0.9 mm2 vs 12.8 ± 0.5 mm2 ; P < 0.05) compared with controls. CONCLUSION: Peripheral nerve hypervascularity is detectable by ultrasonography in moderate to severe diabetic neuropathy with prominent sensory dysfunction.

7T MR neurography-ultrasound fusion for peripheral nerve imaging.

BACKGROUND: We present one patient with an initial diagnosis of Guillain-Barré syndrome (GBS) and one with Charcot-Marie-Tooth disease (CMT) type 1A. METHODS: Both patients underwent ankle tibial nerve fusion-imaging of high-resolution ultrasound (HRUS) with 7T MR neurography (MRN). RESULTS: In GBS, the nerve was enlarged, T2-hyperintense, and showed increased vascularization 21 months after symptom onset. In CMT1A, the enlarged nerve was T2-isointense with normal endoneurial blood flow. CONCLUSIONS: We demonstrate the utility of 7T-MRN-HRUS-fusion-imaging. In GBS, there was evidence of ongoing inflammation resulting in a changed diagnosis to acute-onset chronic demyelinating polyradiculoneuropathy and maintenance of immunotherapy. By MRN-HRUS-fusion, patients with presumed peripheral axonal degeneration could be shown to display imaging markers associated with peripheral nervous system inflammation. Thus, more accurate identification of a treatable inflammatory component may become possible.

Corkscrew Collateral Vessels in Buerger Disease: Vasa Vasorum or Vasa Nervorum.

PURPOSE: To investigate the origin of "corkscrew" collateral vessels around the occluded popliteal artery in patients with Buerger disease by Doppler ultrasound (US) and magnetic resonance (MR) imaging in tandem with digital subtraction angiography (DSA). MATERIALS AND METHODS: Between January 2013 and June 2015, 42 patients diagnosed with Buerger disease were identified retrospectively. Patients in whom occlusion of the popliteal artery was found on DSA of the lower extremity were subjected to Doppler US and MR imaging prospectively. Fifteen of 42 patients were identified as having the required characteristics, of whom 10 participated in the present study. RESULTS: Ten patients with occlusion of the popliteal artery were selected for inclusion, and 12 lower limbs of these patients were investigated. The study cohort comprised one woman and nine men with a mean age of 41 years ± 10 (standard deviation; range, 39-58 y). Corkscrew collateral vessels identified on DSA examinations were also identified on secondary imaging (Doppler US and MR imaging) in all patients except one in whom the popliteal artery was reconstituted after short-segment occlusion. The origin of the corkscrew collateral vessels was identified as the vasa nervorum of the tibial nerve in nine patients. CONCLUSIONS: Data from the present study suggest that corkscrew collateral vessels at the knee level in patients with Buerger disease originate from the vasa nervorum of the tibial nerve rather than the vasa vasorum of the popliteal artery if the latter is occluded.

Similarities and dissimilarities of the blood supplies of the human sciatic, tibial, and common peroneal nerves.

The aim was to investigate the arterial supply of the sciatic, tibial, and common peroneal nerves. Thirty-six lower limbs of 18 human fetuses were studied. The fetuses had been fixed in buffered formalin and the blood vessels injected with barium sulfate. Fetal age ranged from 12 to 28 weeks of gestation. Microdissection of the fetal lower extremities was done under ×5 magnifying lenses. The sciatic nerves of 10 lower extremities were dissected and excised and radiographs taken. The extraneural arterial chain of the sciatic nerve was composed of 2-6 arterial branches of the inferior gluteal artery, the medial circumflex femoral artery, the perforating arteries, and the popliteal artery. The extraneural arterial chain of tibial nerve was composed of 2-5 arteries, which were branches of the popliteal, the peroneal, and the posterior tibial arteries. Radiographs showed the presence of complete intraneural arterial chains in the sciatic and tibial nerves, formed from anastomosing vessels. Dissection showed that, in 97.2% of the specimens, the common peroneal nerve was supplied only by one popliteal artery branch, the presence of which was confirmed radiologically. The sciatic and tibial nerves are supplied by numerous arterial branches of different origins, which provide for collateral circulation. In contrast, the common peroneal nerve is most frequently supplied only by one elongated longitudinal blood vessel, a branch of the popliteal artery. Such a vascular arrangement may make the common peroneal nerve less resistant to stretching and compression.

Common peroneal and posterior tibial ischemic nerve damage, a rare cause.

A 56-year old gentleman presented to our orthopaedic foot and ankle clinic, with unusual symptoms in his left foot. He described a tight sensation over his toes, "like sandpaper under his skin". The pain had started post operatively following a bilateral aorto-femoral bypass. He was subsequently investigated and found to have an ischemic lesion Identified in his common peroneal and posterior tibial nerve with associated muscle atrophy on EMG. This represents a previously unreported complication of aorto-femoral bypass surgery.

Remodeling of myelinated fibers and internal capillaries in distal peripheral nerves following aerobic exercise in aged rats.

The aim of this study was to determine whether aerobic exercise (AE) in old age contributes to improving the morphologies of myelinated fibers (MFs) in peripheral nerves as well as capillaries. Furthermore, we investigated whether such processes are associated with complementary activity of brain-derived neurotrophic factor (BDNF) and vascular endothelial growth factor (VEGF) in the circulating blood and peripheral nerve tissue. Fourteen male Wistar rats (age: 95 wk) were randomly divided into moderate AE ( n = 8) and sedentary (SED; n = 6) groups. Rats in the AE group performed treadmill running for 1 h per day for 2 wk, following which the bilateral tibial nerves of the two groups were removed to examine MF and capillary structure. Levels of BDNF and VEGF in the serum and peripheral nerves were analyzed via enzyme-linked immunosorbent assay. Myelin thickness, axon diameter, and capillary luminal diameter were significantly larger in the AE group than in the SED group ( P < 0.0001). Levels of serum BDNF and VEGF were significantly lower and higher, respectively, in the AE group than in the SED group ( P < 0.001). Conversely, BDNF and VEGF levels in tibial nerve tissue were significantly higher, respectively, and lower in the AE group than in the SED group ( P < 0.001). In conclusion, our study indicates that regular AE induces enlargement of the capillaries and thickens the myelin in aged peripheral nerves, likely via a complementary process involving BDNF and VEGF. NEW & NOTEWORTHY Accumulating evidence indicates that age-related sarcopenia is accompanied by the degeneration of myelinated fibers (MFs) in peripheral nerves. Our study indicates that regular aerobic exercise contributes to increased thickness of the myelin surrounding MFs and enlargement of the capillaries, likely via a complementary process involving brain-derived neurotrophic factor and vascular endothelial growth factor. Our findings demonstrate that regular, moderate-intensity aerobic exercise may help to prevent and reverse peripheral nerve regression in older adults.

Reversal of experimental diabetic neuropathy by VEGF gene transfer.

The pathogenetic basis for diabetic neuropathy has been enigmatic. Using two different animal models of diabetes, we have investigated the hypothesis that experimental diabetic neuropathy results from destruction of the vasa nervorum and can be reversed by administration of an angiogenic growth factor. Nerve blood flow, as measured by laser Doppler imaging or direct detection of a locally administered fluorescent lectin analogue, was markedly attenuated in rats with streptozotocin-induced diabetes, consistent with a profound reduction in the number of vessels observed. A severe peripheral neuropathy developed in parallel, characterized by significant slowing of motor and sensory nerve conduction velocities, compared with nondiabetic control animals. In contrast, 4 weeks after intramuscular gene transfer of plasmid DNA encoding VEGF-1 or VEGF-2, vascularity and blood flow in the nerves of treated animals were similar to those of nondiabetic control rats; constitutive overexpression of both transgenes resulted in restoration of large and small fiber peripheral nerve function. Similar experiments performed in a rabbit model of alloxan-induced diabetes produced comparable results. These findings support the notion that diabetic neuropathy results from microvascular ischemia involving the vasa nervorum and suggest the feasibility of a novel treatment strategy for patients in whom peripheral neuropathy constitutes a secondary complication of diabetes.

Acupuncture treatment improves nerve conduction in peripheral neuropathy.

The etiology of peripheral neuropathy (PN) often remains elusive resulting in a lack of objective therapeutic strategies. We conducted a pilot study to evaluate the therapeutic effect of acupuncture on PN as measured by changes in nerve conduction and assessment of subjective symptoms. One hundred and ninety-two consecutive patients with PN as diagnosed by nerve conduction studies (NCS) were evaluated over a period of 1 year. Of 47 patients who met the criteria for PN of undefined etiology, 21 patients received acupuncture therapy according to classical Chinese Medicine as defined by the Heidelberg Model, while 26 patients received the best medical care but no specific treatment for PN. Sixteen patients (76%) in the acupuncture group improved symptomatically and objectively as measured by NCS, while only four patients in the control group (15%) did so. Three patients in the acupuncture group (14%) showed no change and two patients an aggravation (10%), whereas in the control group seven showed no change (27%) and 15 an aggravation (58%). Importantly, subjective improvement was fully correlated with improvement in NCS in both groups. The data suggest that there is a positive effect of acupuncture on PN of undefined etiology as measured by objective parameters.

Arterial Anatomy of the Posterior Tibial Nerve in the Tarsal Tunnel.

BACKGROUND: Both vascular and compression etiologies have been proposed as the source of neurologic symptoms in tarsal tunnel syndrome. Advancing the understanding of the arterial anatomy supplying the posterior tibial nerve (PTN) and its branches may provide insight into the cause of tarsal tunnel symptoms. The purpose of this study was to describe the arterial anatomy of the PTN and its branches. METHODS: Sixty adult cadaveric lower extremities (thirty previously frozen and thirty fresh specimens) were amputated distal to the knee. The vascular supply to the PTN and its branches was identified, measured, and described macroscopically (the thirty previously frozen specimens, prepared using a formerly described debridement technique) and microscopically (the thirty fresh specimens, processed using the Spälteholz technique). RESULTS: On both macroscopic and microscopic evaluation, the PTN and the medial and lateral plantar nerves were observed to have multiple entering vessels within the tarsal tunnel. On microscopic evaluation, a vessel was observed to enter the nerve at the bifurcation of the PTN into the medial and lateral plantar nerves in twenty-two (73%) of the thirty specimens. There was a significant difference (p < 0.05) in vascular density between the PTN and each of its branches. CONCLUSIONS: The abundant blood supply to the PTN and its branches identified in this study is consistent with observations of other peripheral nerves. This rich vascular network may render the PTN and its branches susceptible to nerve compression related to vascular congestion. The combination of vascular and structural compression may also elicit neurologic symptoms. CLINICAL RELEVANCE: Advancing the understanding of the arterial anatomy supplying the PTN and its branches may provide insight into the cause and treatment of tarsal tunnel syndrome.

Spatial distribution of nerve injury after occlusion of individual major vessels in rat sciatic nerves.

In an attempt to better understand the spatial distribution of ischemic injury secondary to occlusion of major arteries, we measured nerve blood flow (NBF) and studied morphologic changes at various levels distal to the ligature site. Arterial ligation of the femoral, internal iliac, or superior gluteal artery was preceded and followed by measurement of NBF using laser Doppler flowmetry which helped identify "watershed areas" and guided the sampling process as nerves were examined pathologically and areas of injury were identified. Femoral artery ligation produced the most severe ischemia, focally reducing NBF by 80% in the tibial nerve at a level just below the knee. Within these ischemic nerve segments there were degenerative changes of nerve fibers seen mainly in the subperineurial region. Ligation of the internal iliac artery caused an approximately 60% reduction in NBF at the upper and mid-thigh levels of the sciatic nerve which resulted only in endoneurial edema in tissue taken at this level. Following superior gluteal artery ligation. NBF was reduced by only 20% at the pelvic level of the sciatic nerve and there was neither endoneurial edema nor fiber abnormalities. This study demonstrates the watershed pattern of ischemic injury associated with single vessel ligation by correlating neuropathologic change with quantitative measures of local nerve blood flow. The data further support the concept that mild levels of ischemia cause endoneurial edema, while moderate levels of ischemia produce demyelination and severe ischemia produces Wallerian degeneration.

Blood-nerve and blood-brain barrier permeabilities and nerve vascular space in Fischer-344 rats of different ages.

The permeability-surface area product (PA) of [3H]- or [14C]sucrose at the blood-nerve barrier (BNB) of the sciatic nerve; and at the blood-brain barrier (BBB), were determined in Fischer-344 rats at 3, 11 and 31 months of age. PA was determined by using an in vivo i.v. bolus injection of radiotracer with two-time point graphic and quantitative autoradiographic methods. Vascular space and water content of the tibial nerve of these rats also were determined using quantitative morphometry and dry and wet weight ratios, respectively. There was no significant difference between mean PA(BNB) in any age group [(PA(BNB) at 3 months = 1.2 +/- 0.1 (mean +/- S.E.), at 11 months = 1.8 +/- 0.3; and at 31 months = 1.4 +/- 0.2 x 10(5) ml/s . g wet wt; n = 5-8 rats], nor any difference in PA(BBB). The mean ratio (%) of surface area of endoneurial blood vessels/nerve cross-section of the tibial nerve also did not differ between any group [3 months: 16 +/- 2 vessels; mean surface area ratios = 2.20 +/- 0.10%, n = 5; 11 months: 22 +/- 3 vessels and 2.48 +/- 0.21%, n = 5; 11 months: 22 +/- 3 vessels and 2.48 +/- 0.21%, n = 5; and at 31 months: 26 +/- 1 vessels and 2.40 +/- 0.23%, n = 4). The mean nerve water in rats at 31 months was 64.8 +/- 1.1% wet wt and did not differ from that at 11 months (66.0 +/- 0.6% wet wt) or at 3 months (65.1 +/- 1.0% wet wt) (n = 5-8 nerves). Our results indicate that BBB and BNB integrities are not altered in senescent Fischer-344 rats.

Complex regional pain syndrome type I (RSD): pathology of skeletal muscle and peripheral nerve.

BACKGROUND: Reflex sympathetic dystrophy (RSD) (recently reclassified as complex regional pain syndrome type I) is a syndrome occurring in extremities and, when chronic, results in severe disability and untractable pain. RSD may be accompanied by neurologic symptoms even when there is no previous neurologic lesion. There is no consensus as to the pathogenic mechanism involved in RSD. To gain insight into the pathophysiology of RSD, we studied histopathology of skeletal muscle and peripheral nerve from patients with chronic RSD in a lower extremity. METHODS: In eight patients with chronic RSD, an above-the-knee amputation was performed because of a nonfunctional limb. Specimens of sural nerves, tibial nerves, common peroneal nerves, gastrocnemius muscles, and soleus muscles were obtained from the amputated legs and analyzed by light and electron microscopy. RESULTS: In all patients, the affected leg showed similar neurologic symptoms such as spontaneous pain, hyperpathy, allodynia, paresis, and anesthesia dolorosa. The nerves showed no consistent abnormalities of myelinated fibers. In four patients, the C-fibers showed electron microscopic pathology. In all patients, the gastrocnemius and soleus muscle specimens showed a decrease of type I fibers, an increase of lipofuscin pigment, atrophic fibers, and severely thickened basal membrane layers of the capillaries. CONCLUSION: In chronic RSD, efferent nerve fibers were histologically unaffected; from afferent fibers, only C-fibers showed histopathologic abnormalities. Skeletal muscle showed a variety of histopathologic findings, which are similar to the histologic abnormalities found in muscles of patients with diabetes.

Effect of rhTNF-alpha injection into rat sciatic nerve.

To assess whether TNF-alpha causes inflammatory demyelination or axonal degeneration, we injected into rat sciatic nerve saline, 100 U and 1000 U of rhTNF-alpha and studied the electrophysiological and pathological effects. At day 1 electrophysiology showed a slight reduction of proximal compound muscle action potential amplitude and pathology showed edema, inflammatory infiltration of vessel walls and endoneurium only in nerves injected with 1000 U of rhTNF-alpha. At day 5, there was no demyelination and a percentage of degenerated fibers similar in the three groups. To study the blood-nerve barrier, fluorescein isothiocyanate-labelled albumin was given intravenously after intraneural injection. The nerves injected with 1000 U rhTNF-alpha showed a leakage of the tracer in the endoneurium. TNF-alpha does not appear, at the doses used, to have myelinotoxic or axonopathic properties. The electrophysiological effect at day 1 may be due to mechanical compression of nerve fibers as a result of the blood-nerve barrier damage with consequent endoneurial edema.

Effect of perineurial window size on nerve regeneration, blood-nerve barrier integrity, and functional recovery.

End-to-side neurorrhaphy is used clinically to reconstruct nerve injuries when the lack of a suitable proximal nerve stump precludes conventional approaches to microsurgical repair. In end-to-side neurorrhaphy, the distal stump of a transected nerve is sutured to the side of an intact nerve that serves as an axon donor. Prior studies suggest that this perineurial window is a prerequisite for effective nerve regeneration into the recipient nerve. However, the optimal size for this perineurial window remains uncertain. This study evaluated the effect of perineurial window size on collateral axonal sprouting, blood-nerve barrier architecture, and functional impairment of the donor nerve. One hundred twenty Lewis rats were randomized to 1 and 5 mm perineurial window groups and examined at serial time points. The 5 mm perineurial window group exhibited significantly greater fiber counts at the repair zone than the 1mm group within 4 weeks (p < 0.005). Marked breakdown of the blood-nerve barrier was present 2 week postoperatively and resolved by 4 weeks regardless of 1 versus 5 mm perineurial window size. Tibial function indices in both groups normalized between 4 and 6 weeks postoperatively. A large (5 mm) perineurial window induced greater collateral sprouting or regenerative response than a small (1 mm) perineurial window without increasing cross sectional nerve injury or delaying functional recovery.

Distribution of adrenergic innervation of blood vessels in peripheral nerve.

The distribution of adrenergic innervation of microvessels in the extrafascicular and endoneurial compartments of rat tibial nerve was examined with glyoxylic acid-induced and formaldehyde-induced histofluorescence methods. Periarterial and arteriolar adrenergic nerves were present in the epineurium-perineurium suggesting that blood flow in the extrafascicular connective tissue is under neurogenic influence. In contrast, blood vessels in the nerve endoneurium were not associated with histofluorescent nerve fibers. The absence of perivascular adrenergic innervation in the endoneurium suggests that regulation of vascular function within the endoneurium is not under neurogenic control.

Axonal elongation through long acellular nerve segments depends on recruitment of phagocytic cells from the near-nerve environment. Electrophysiological and morphological studies in the cat.

The distal nerve stump plays a central role in the regeneration of peripheral nerve but the relative importance of cellular and humoral factors is not clear. We have studied this question by freezing the tibial nerve distal to a crush lesion in cat. The importance of constituents from the near-nerve environment was assessed by modification of the contact between the tibial nerve and the environment. Silicone cuffs, containing electrodes for electrophysiological assessment of nerve regeneration, were placed around the tibial nerve distal to the crush site. The interaction between long acellular frozen nerve segments (ANS) and the near-nerve environment was ascertained by breaching the silicone cuff to allow access of cellular or humoral components. Tibial nerves were crushed and frozen for 40 mm and enclosed in nerve cuffs with 0.45-microm holes or 2.0-mm holes to allow access of humoral factors or tissue ingrowth, respectively. In a second set of experiments, tibial nerves were crushed and either frozen for 20+20 mm, leaving a 10 mm segment with viable cells in the center (stepping-stone segment) or frozen for 50 mm. These nerves were enclosed in cuffs with 2.0 mm holes corresponding to the viable nerve segment. The regeneration was monitored electrophysiologically by implanted electrodes and after 2 months the nerves were investigated by light and electron microscopy. The results indicate that soluble substances in the near-nerve environment, such as nutrients, oxygen or tropic substances did not exert any independent beneficial effect on the outgrowing axons. However, phagocytic cells entering the acellular segment from the near-nerve environment were crucial for axonal outgrowth in long ANS.

Hypothermic neuroprotection of peripheral nerve of rats from ischemia-reperfusion injury: intraischemic vs. reperfusion hypothermia.

The pathophysiology of ischemic fiber degeneration (IFD) is not known, but mechanisms involved during nerve ischemia differ from those during reperfusion. We have previously demonstrated hypothermic neuroprotection of peripheral nerve from IFD. We now evaluate the efficacy of hypothermia in the intraischemic vs. the reperfusion period, using our established model of ischemia-reperfusion injury. Intraischemic hypothermia resulted in significant recovery of all indices (behavior score, electrophysiology and histology, P<0.01 or 0.05) while hypothermia during reperfusion period showed less improvement, significant only for the histological score compared to normothermia group (IFD index, P<0.05). Once hypothermia was applied in the ischemic period, the resultant neuroprotection continued into the reperfusion period, even if nerve temperature was then raised during the reperfusion period. These results indicate that hypothermic neuroprotection is more efficacious during the intraischemic period than during reperfusion, when a lesser degree of neuroprotection ensued.

The expression of proinflammatory cytokine mRNA in the sciatic-tibial nerve of ischemia-reperfusion injury.

We evaluated the proinflammatory cytokines, TNF-alpha and IL-1beta, mRNA expression in the rat sciatic and tibial nerves following ischemia-reperfusion (IR) injury, using competitive RT-PCR, to explore the role of cytokines in IR injury. The expressions of both TNF-alpha and IL-1beta mRNA were related to severity of ischemia and occurred with reperfusion rather than ischemia alone. TNF-alpha gene expression peaked at 24 h of reperfusion, while that of IL-1beta peaked at 12 h. These data support the notion that the proinflammatory cytokines TNF-alpha and IL-1beta are involved in the inflammatory response of IR injury to the peripheral nervous system and may be involved in the pathophysiology of ischemic fiber degeneration.

Progression of regeneration after nerve infarction.

We performed morphologic studies on the progression of regeneration in cat hind limb nerves after acute ischemic injury. None of the damaged nerve trunks showed a major increase in endoneurial connective tissue. Despite this fact, regeneration of nerve with transfascicular infarct was far from complete even 16 months after injury as manifested by a striking increase in the small myelinated fibers (MF) number and decrease in large MF number. Restoration of infarcted nerves was less complete than that previously reported after a nerve crush. Changes in the necrotic nerve segment and difficulty in making target contact with muscle and other tissues damaged by ischemia may be limiting factors in the regeneration of infarcted nerves.

Guanethidine-induced adrenergic sympathectomy augments endoneurial perfusion and lowers endoneurial microvascular resistance.

Chronic administration of guanethidine sulfate in the rat induces a selective adrenergic neuropathy. We studied the effects of guanethidine-induced adrenergic sympathectomy on rat sciatic nerve blood flow (NBF), microvascular resistance (MR), vessel caliber and norepinephrine (NE) content. A control group of animals was studied following chronic administration of mammalian Ringer's solution. NBF and MR were measured with an endoneurial microelectrode, using the technique of hydrogen clearance (HC). Following HC, the sciatic nerve was perfused with India Ink, removed, frozen and sectioned. Measurements were made of endoneurial microvessel numbers, diameter, circumference and area. The contralateral sciatic nerve was removed for measurements of NE content. In guanethidine-treated animals we observed elevated NBF, reduced MR and dilated microvessels. Numbers of microvessels and fascicular areas were similar to controls. NE content was markedly reduced following sympathectomy. These studies suggest that NBF, unlike cerebral blood flow (CBF), is regulated by its adrenergic input. Removal of adrenergic innervation of the vasa nervorum appears to result in a loss of tonic vasoconstrictive action.