Are there motor fibers in the sural nerve?

A case of anomalous innervation of the abductor digiti quinti of the foot (ADQ) via the sural nerve is described. A muscle action potential from the ADQ could be elicited by stimulation of both the sural and the posterior tibial nerves.     

Clinical utility of dorsal sural nerve conduction studies

A technique of testing sensory nerve conduction of the dorsal sural nerve in the foot was used in 38 normal subjects and 70 patients with peripheral neuropathies. The normal dorsal sural sensory nerve action potential (SNAP) had a mean amplitude of 8.9 microV (range 5-15 microV), mean latency to negative peak of 4.0 ms (range 3.2-4.7 ms), and mean conduction velocity of 34.8 m/s (range 30-44 m/s). Optimal placement of the recording electrodes to obtain a maximal nerve action potential was proximal to digits 4 and 5. Cooling to below 25 degrees C prolonged the latency but did not decrease the SNAP amplitude. Among the patients with peripheral neuropathy, dorsal sural SNAP was absent in 68 (97%), whereas only 54 (77%) showed abnormalities of sural sensory conduction. The diagnostic sensitivity of sensory nerve conduction studies in peripheral neuropathies may be significantly improved by the use of this technique for evaluating the action potential of the dorsal sural nerve.     

Ultrasound guidance for sural nerve conduction studies

Introduction: Ultrasound can potentially identify nerves and guide recording and stimulating electrode placement for nerve conduction studies (NCS). This prospective study was performed to determine whether ultrasound guidance of sural NCS results in higher action potential amplitude, fewer stimuli required, lower stimulus strength required, and less pain experienced. Methods: Fourteen healthy individuals underwent bilateral sural NCS, both with and without ultrasound guidance. Studies were separated by at least 48 h, and the order of testing was randomly assigned. Results: Ultrasound guidance resulted in significantly fewer stimuli and lower stimuli strength required to obtain supramaximal responses (P < 0.01–0.03). Ultrasound guidance required significantly more time to perform than standard sural NCS (P < 0.01). There was no difference in sural nerve amplitude or pain rating between the 2 groups. Discussion: Neuromuscular ultrasound can be used effectively to guide electrode placement during sural NCS. Muscle Nerve 59:705–707, 2019     

Discomfort after fascicular sural nerve biopsy

Sural nerve biopsy may, in selected cases, give valuable information in the investigation of patients with polyneuropathy. The prevalence and severity of patient discomfort after fascicular nerve biopsy was investigated in 67 patients by a mailed questionnaire. A lasting (greater than 6 months) significant discomfort was found in 6 patients (11%), in 3 of these the symptoms were graded as severe. Thus, sural nerve biopsy should be limited to cases in which important information may be expected and the patients should be carefully informed of the risks of long-lasting discomfort.     

An ultrasound study of anatomic variants of the sural nerve

Introduction: There are anatomic variations of the sural nerve (SN). Knowledge of these morphological types and the length of the SN are important for planning surgical reconstruction of peripheral nerves. Our purpose was to classify the morphological types of the SN by using ultrasound. Methods: Two‐hundred SNs in 100 normal subjects were examined by ultrasound with 13‐MHz linear‐array transducers. Classification of the SN was evaluated by its formation. The distance between the union and the distal point of the lateral malleolus was measured. Results: SN variants could be classified into three types: type I (81%); type II (18%); and type III (1%). In type I, the average length of the SN was 15.8 ± 5.7 cm. Conclusions: The morphological types of the SN can be determined using ultrasound. Ultrasound classification of the SN is useful with regard to donor nerve surgical reconstruction of peripheral nerves. Muscle Nerve, 2011     

Occupational neuropathy of the sural nerve

A 20-year-old carpet-layer with compression of the right sural nerve due to the peculiar posture maintained during his work is described, and electromyographic findings are presented.

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Sommario Il presente lavoro riporta i risultati ottenuti dallo studio elettromiografico eseguito su un posatore di “moquette” di 20 anni affetto da una compressione del nervo surale destro causata dalla peculiare postura mantenuta durante il lavoro.

     

Electrophysiological mapping of the segmental innervation of the saphenous and sural nerves

Delineation of an area of sensory loss is often helpful in localizing a lesion at the spinal or root level. We have studied the segmental innervation of two cutaneous nerves, the saphenous and the sural, during selective posterior rhizotomy. Each nerve was stimulated electrically, and recordings were made from dorsal roots L-3 to S-2 in 30 patients. We found that both nerves received innervation through at least three spinal levels. The level of maximum innervation was approximately equally divided between L-3 and L-4 for the saphenous nerve. The sural nerve received maximum innervation through S-1 in 80% of the cases, but the remainder came through L-5 or S-2. These findings provide electrophysiologic evidence that these cutaneous nerves have multiple segmental supply, and the sensory area they supply does not lie solely within a single dermatome.© 1993 John Wiley & Sons, Inc.     

Anomalous origin of the sural nerve in a patient with tibial—common peroneal nerve anastamosis

Recognition of anomalous innervation patterns may be important in dealing with peripheral nerve injuries. We describe a patient who suffered injury to the common peroneal nerve (CPN) at the knee when he laterally dislocated his knee. Intraoperative nerve conduction studies during surgical exploration revealed that nerve fibers from the tibial nerve crossed over to join the CPN immediately distal to a neuroma incontinuity. The sural nerve was also found to arise totally from the CPN. © 1993 John Wiley & Sons, Inc.     

Sequelae following sural nerve biopsy in type 1 diabetic subjects

Objectives –  To detect post-operative sequelae of sural nerve biopsy.
Materials and methods––  A questionnaire mailed to type 1 diabetic patients ( n  = 24; male/female 23/1; reply n  = 23) 2 years after biopsy.
Results –  Type 1 diabetic patients (age 56 [11]; median [interquartile range]) had a long duration of diabetes (DM; 20 [19] years) and all had neuropathy. Three out of 24 patients developed infection (two superficial and one deep) and one had a post-operative bleeding. Less frequent pain among the patients were reported from one centre. About one-third or more of the patients still complained of pain, mostly mild, in the biopsy area and paraesthesia in the foot 2 years after surgery. More than two-thirds of the patients were reluctant for further biopsy; a crucial information in drug trial planning.
Conclusions –  Sequelae of a sural nerve biopsy occur in type 1 DM. The risk for wound infections should be considered.     

A comparison of sural nerve conduction studies in patients with impaired oral glucose tolerance test

OBJECTIVE: Monitoring of the sural nerve is a sensitive method for detection of neuropathies. We examined different methods of studying sural nerve conduction in a group of patients with impaired glucose tolerance (IGT) in the same study. MATERIALS AND METHODS: Several parameters of sural nerve were investigated in 20 patients. First, sensory nerve conduction studies of the sural nerve were performed on the distal-leg and the proximal-leg segments. Second, dorsal sural nerve studies were conducted. Third, the sural/radial sensory nerve action potential (SNAP) amplitude ratios were calculated. The results were compared with those obtained from 21 healthy controls. RESULTS: Abnormal results revealing peripheral neuropathy were found in only one patient and dorsal sural SNAP was absent in another patient (5%). Although the results of nerve conduction studies were within normal ranges except the patient with peripheral neuropathy, the lower extremity nerves and especially sural nerves have been found to be more affected and the parameters revealed large differences between groups (P < 0.05). Only dorsal sural nerve latency related to fasting blood glucose level in patients (<0.05). DISCUSSION AND CONCLUSIONS: Sural nerve studies should be of value to determine neuropathy in IGT patients. This study supported the idea that IGT is a transitional state before diabetes and also the importance of the dorsal sural nerve latencies for early detection of neuropathy.     

Conduction studies of the normal sural nerve.

The sural nerve was studied orthodromically using the near-nerve technique in 273 normal subjects (155 females, 118 males) aged 5 to 90 years. The sensory action potential (SAP), evoked at the dorsum of the foot, was recorded at the lateral malleolus and midcalf, and at the midcalf when evoked at the lateral malleolus. In addition, the SAP was recorded at intermediate distal sites and at proximal sites at the popliteal fossa, the gluteal fold, and the S-1 root. The amplitude of the SAP recorded at midcalf was 32% higher in females than in males. This was probably due to volume-conduction properties, as differences between genders were less noticeable at more distal recording sites. The amplitude decreased steeply and exponentially with age. Conduction distance had a strong influence on the amplitude of the SAP, which decreased with increasing distance following a power relationship with an exponent of 1.4 to 1.7. This decrease was due to temporal dispersion with decreased summation and increased phase cancellation. The conduction velocity was slightly lower along the very distal course of the nerve than along more proximal segments.     

Usefulness of sural nerve biopsy in the genomic era

The value of peripheral nerve biopsy is now sometimes questioned due to the high complication rate and the recent development of noninvasive molecular techniques for diagnosis of hereditary neuropathy. However, the disorders that can be diagnosed by genetic analysis are limited and sural nerve biopsy is still a powerful tool for making a correct diagnosis of peripheral neuropathy. Histological evaluation of the sural nerve has long focused on changes of the two major components of peripheral nerves, axons and myelin, as well as on the detection of diagnostic changes such as amyloid deposits, sarcoid tubercles, and vasculitis. In addition to these components, the sural nerve biopsy specimen contains various important cells, including perineurial cells, mast cells, endothelial cells, pericytes, and lymphocytes. Among these cells, the endothelial cells and pericytes form the blood‐nerve barrier (BNB) and investigation of these cells can reveal important information, especially in inflammatory neuropathies. To better understand the biological basis of BNB, we established rat and human immortal cell lines from the endothelial cells and pericytes of endoneurial microvessels. Characterization of these cell lines is now underway at our laboratory. These BNB cell lines should provide useful information concerning the pathophysiology of peripheral neuropathy, and we should obtain a new perspective for the investigation of nerve biopsy specimens after understanding the molecular background of the BNB.     

Is quantitation necessary for assessment of sural nerve biopsies?

In this study we measured the reliability and accuracy of visual assessment of certain features of sural nerve pathology. Three raters visually assessed 20 sural nerves over two sessions. Four features were categorized: (1) myelinated fiber (MF) density; (2) size loss of MFs; (3) thinly myelinated axons; and (4) axonal clusters. Intra- and interrater reliabilities for the categories were determined. Quantitative data were compared with the visual assessments. Percentage agreements for single raters between the two sessions ranged from 35% to 100% and 9 times out of 12 were > or =70%. Interrater reliability, however, showed a kappa-value range of 0.03 (poor) to 0.49 (medium). In 85% of cases, visual ratings were within one category of the quantitated MF loss. However, visual categorization was poor compared with quantitation for determining size loss of MFs and myelin thickness. Quantitation needs to be considered to aid peripheral nerve pathologists in the assessment of some of the features of sural nerve biopsy specimens.     

Digital electron microscopic examination of human sural nerve biopsies

Diabetic peripheral polyneuropathy is characterized by axonal degeneration and regeneration as well as by Schwann cell and microvascular changes. These changes have been described at both the light (LM) and the electron microscopic (EM) levels; however, EM has not been applied to large clinical trials. Our goal was to adapt the rigorous techniques used for quantifying human biopsies with LM image analysis to accommodate ultrastructural analyses. We applied digital image capture and analysis to the ultrastructural examination of axons in sural nerve biopsies from diabetic patients enrolled in a multicenter clinical trial. The selection of sural nerve biopsies was based on the quality of specimen fixation, absence of physical distortion, and nerve fascicle size (> or =100,000; < or =425,000 microm2). Thin sections were collected on formvar-coated slot grids, stabilized with carbon and scanned on a Phillips CM100 transmission electron microscope. Digital images were captured with a Kodak Megaplus 1.6 camera. A montage was constructed using software derived from aerial mapping applications, and this virtual image was viewed by EM readers. Computer-assisted analyses included identification and labeling of individual axons and axons within regenerating clusters. The average density of regenerating myelinated axon clusters per mm2 was 65.8 +/- 5.1, range of 0-412 (n = 193). These techniques increase the number of samples that may be analyzed by EM and extend the use of this technique to clinical trials using tissue biopsies as a primary endpoint.     

Conduction velocity distributions compared to fiber size distributions in normal human sural nerve

Compound action potentials (CAPs) were recorded from the sural nerve of healthy volunteers. A mathematical technique (inverse modeling) was used to compute conduction velocity (CV) histograms from the data. Results were compared to the morphology of age-matched normal sural nerve biopsies. Coefficients of variation (CoVs) revealed the statistical relationship between morphological data (diameter histograms) and electrophysiological data (CV histograms and conventional CAP parameters). No differences were found for the thick fiber group when comparing the CoVs of the diameter histogram parameters with the corresponding CV histogram parameters. Apparently, the same inherent biological interindividual variability is encountered. The CoVs of the CVs of the CAP's main phases are in good agreement with the CoVs of the estimated mean velocity of the thick fiber group. Inverse modeling increases the reliability of the estimation of the number of active fibers as compared to direct CAP amplitude interpretation.© 1995 John Wiley & Sons, Inc.     

Electrical stimulation reveals relatively ineffective sural nerve projections to dorsal horn neurons in the cat

Electrical stimulation of the sural nerve (SN) revealed input from sural nerve afferents to L6 and L7 dorsal horn neurons that were not apparent using natural mechanical stimuli, especially in cells with variable latency responses to SN stimulation. Nearly all (31/32) cells that had reliable, fixed latency responses to SN stimulation also had an excitatory receptive field (RF) in the region of skin innervated by the sural nerve (SN region). About one-third (20/57) of the cells with variable latency responses to SN stimulation, however, had an RF outside the SN region. Most (130/146) cells with no response to SN stimulation had RFs outside the SN region. There were no obvious differences between variable latency cells with RFs in the SN region vs those with RFs outside it in latency of response to SN stimulation, recording depth, RF sizes or modality properties. In a subsample of 31 postsynaptic dorsal column neurons all cells responding to SN stimulation also had an RF in the SN region. Strengthening of relatively ineffective projections from the sural nerve by lesions might be expected to lead to an increase in the proportion of cells responding with impulses to natural stimulation of the skin innervated by the sural nerve, and, hence, to an increase in average RF size.     

Increased response to sural nerve input in the dorsal horn following chronic spinal cord hemisection

Monosynaptic input from sural nerve afferents to dorsal horn neurons was mapped bilaterally using electrical stimulation in normal cats and cats with spinal cord hemisections. Animals hemisected 6 h-5 days previously did not differ significantly from normals and the sides of the cord did not differ in either group. In animals hemisected 88–182 days previously there were significantly more sites responsive to sural nerve input ipsilateral to the hemisection, than contralateral to it.     

Regeneration of perivascular adrenergic innervation in rat tibial nerve after nerve crush

Summary Adrenergic innervation of blood vessels in the rat tibial nerve during degeneration and regeneration was studied using the formaldehyde-induced fluorescence method. The left sciatic nerve was crushed with suture threads to produce a 4-mm length of crushed nerve. At 1, 3, 7, 14, 28, 56 and 84 days after nerve crush, degenerative and regenerative changes in the nerve were verified using light microscopy. At each time point, adrenergic innervation was examined in epi-perincurial whole mount and nerve cross-section preparations. One day after nerve crush, fluorescence of adrenergic nerve fibers in the endoneurium was absent. Fluorescent adrenergic nerve fibers reappeared in the endoneurium at day 56 and reached the control density by 84 days. In the epi-perineurium, adrenergic innervation of small and medium-size arterioles was absent at 3 days, in large arterioles at 7 days. At 56 days, all epi-perineurial arterioles were reinnervated by a faint, sparse adrenergic network, which reached the control density at 84 days. The results suggest that adrenergic innvervation in the rat peripheral nerve is lost during nerve degeneration, but recovers when the nerve has regenerated.