Misinterpretation of sural nerve conduction studies due to anatomical variation

Deep peroneal neuropathy induced by prolonged squatting: a case report

Prolonged squatting is a well-documented cause of common peroneal neuropathy, wherein the common peroneal nerve is thought to be compressed between the biceps femoris tendon and the lateral head of the gastrocnemius muscle or the fibular head. However, deep peroneal neuropathy resulting from prolonged squatting has not been previously reported. We present the case of a tile installer who developed unilateral deep peroneal neuropathy following extended squatting, diagnosed through ultrasonography, which identified the bilateral division of the common peroneal nerves between the knee joint and the fibular head. This case underscores the value of ultrasonography, particularly when electrodiagnostic results are inconsistent with clinical expectations.

Variations in sural nerve formation and course in fetuses

To investigate variations regarding the formation and course of the sural nerve (SN). We dissected 60 formalin-fixed Brazilian fetuses (n = 120 lower limbs) aged from the 16th to 34th weeks of gestational age. Three incisions were made in the leg to expose the SN, and the gastrocnemius muscle was retracted to investigate the SN course. Statistical analyses regarding laterality and sex were performed using the Chi-square test. Eight SN formation patterns were classified after analysis. Type 4 (in which the SN is formed by the union of the MSCN with the LSCN) was the most common SN formation pattern. Although there was no statistical association between the formation patterns and the lower limb laterality (p = 0.9725), there was as to sex (p = 0.03973), indicating an association between anatomical variation and sex. The site of branch joining was in the distal leg most time (53.75%). In all lower limbs, the SN or its branches crossed from the medial aspect of the leg to the lateral margin of the calcaneal tendon (CT). Most often, the SN is formed by joining the MSCN and the LSCN in the distal leg. The SN or its branches ran close to the saphenous vein, crossed the CT from medial to lateral, and distributed around the lateral malleolus.

Anatomical patterns of the sural nerve: a meta-analysis with clinical and surgical considerations

BACKGROUND

The sural nerve (SN) supplies the posterolateral aspect of the leg and the lateral aspects of the ankle and foot and descends through the gastrocnemius muscle along the lower third of leg. Because in-depth knowledge about SN anatomy is essential for clinical and surgical approaches, our study aims to review SN anatomical patterns.

METHODS

We searched the PubMed, Lilacs, Web of Science, and SpringerLink databases to find relevant articles for meta-analysis. We assessed the quality of the studies using the Anatomical Quality Assessment tool. We used proportion meta-analysis to analyze the SN morphological variables and simple mean meta-analysis to analyze the SN morphometric variables (nerve length and distance to anatomical landmarks).

RESULTS

Thirty-six studies comprised this meta-analysis. Overall, Type 2A (63.68% [95% CI 42.36-82.64]), Type 1A (51.17% [95% CI 33.16-69.04]) and Type 1B (32.19% [95% CI 17.83-48.38]) were the most common SN formation patterns. The lower third of leg (42.40% [95% CI 32.24-52.86]) and middle third of leg (40.00% [95% CI 25.21-53.48]) were the most common SN formation sites. The pooled SN length from nerve formation to the lateral malleolus was 144.54 mm (95% CI 123.23-169.53) in adults, whereas the SN length was 25.10 mm (95% CI 23.20-27.16) in fetuses in the second trimester of gestation and 34.88 mm (95% CI 32.86-37.02) in fetuses in the third trimester of gestation.

CONCLUSIONS

The most prevalent SN formation pattern was the union of the medial sural cutaneous nerve with the lateral sural cutaneous nerve. We found differences regarding geographical subgroup and subject age. The most common SN formation sites were the lower and middle thirds of the leg.

Electrodiagnostic Assessment of Polyneuropathy

This article focuses on principles of nerve conduction studies and needle electromyography applied to the electrodiagnosis of polyneuropathy. The components of the electrodiagnostic evaluation of polyneuropathy and the electrophysiological characteristics of axonal and demyelinating neuropathies and nodo-paranodopathies are reviewed.

Characterization of mononeuropathy of the lateral cutaneous nerve of the calf

INTRODUCTION/AIMS

Isolated injuries to the lateral cutaneous nerve of the calf (LCNC) branch of the common peroneal nerve can cause obscure chronic posterolateral knee and upper calf pain and sensory symptoms. Routine examination and electrodiagnostic testing do not detect them because the LCNC has no motor distribution and it is not interrogated by the typical peroneal nerve conduction study. There are only about 10 prior cases, thus scant physician awareness, so most LCNC injuries remain misdiagnosed or undiagnosed, hindering care.

METHODS

We extracted pertinent records from seven patients with unexplained posterolateral knee/calf pain, six labeled as complex regional pain syndrome, to investigate for mononeuropathies. Patients were asked to outline their skin area with abnormal responses to pin self-examination independently. Three underwent an LCNC-specific electrodiagnostic study, and two had skin-biopsy epidermal innervation measured. Cadaver dissection of the posterior knee nerves helped identify potential entrapment sites.

RESULTS

Initiating events included knee surgery (three), bracing (one), extensive kneeling (one), and other knee trauma. All pin-outlines included the published LCNC neurotome. One oftwo LCNC-specific electrodiagnostic studies revealed unilaterally absent potentials. Longitudinal, controlled skin biopsies documented profound LCNC-neurotome denervation then re-innervation contemporaneous with symptom recovery. Cadaver dissection identified the LCNC traversing through the dense fascia of the proximolateral gastrocnemius muscle insertion.

DISCUSSION

Isolated LCNC mononeuropathy can cause unexplained posterolateral knee/calf pain syndromes. This series characterizes presentations and supports patient pin-mappings as a sensitive, globally available, low-cost diagnostic aid. Improved recognition may facilitate more rapid, accurate diagnosis and, thus, optimize management and improve outcomes.

Anatomy of the sural nerve complex: Unaccounted anatomic variations and morphometric data

BACKGROUND

The sural nerve (SN) is a cutaneous sensory nerve innervating the posterolateral leg. The SN is formed from a highly variable set of contributing nerves called the sural nerve complex (SNC). The SNC is made up of the lateral sural cutaneous nerve, medial sural cutaneous nerve, sural communicating branch, and SN. The SN is frequently cited as the most common donor nerve graft and is commonly injured in procedures of the lower extremity. Recent meta-analysis standardized six morphologies of the SNC and established a required reporting criterion for the group of nerves forming the SN. Due to the inconsistencies in previous literature, this study will group observed SNC's by one of these six SNC morphologies to assess and validate the meta-analysis grouping criteria. This study will also collect the same morphometric data previously outlined in order to grow the number of samples that are reported in a standardized fashion.

METHODS

100 formalin and 4 Theil preserved cadavers (n = 208) lower limbs were bilaterally dissected at Kansas City University and Creighton University School of Dentistry to observe the SNC in its entirety on the posterolateral leg. Anatomic data was captured utilizing the standardized morphologies types 1-6 with two sub-typing. Nerves that were found to be outside of this categorization were placed in an unassigned grouping.

RESULTS

The most prevalent SNCs were type 1 at 41.35% (n = 86) and type 3 nerves at 34.62% (n = 72). Type 2 was found 8.65% (n = 18), type 4 and 5 were found each at 0.48% (n = 1). Type 6 was not observed. When comparing the present studies frequency of nerve types 1-6 to the meta-analysis a sub-grouping of "North American" cadaveric studies a X² = .903 p = .030 was found. Two distinct and previously unassigned formations of the SNC were 10.58% (n = 20) and 3.85% (n = 8) of data. These two SNC are termed type 7 & 8, these represent two formations of SN that are outside of what was previously reported. 15.87% (n = 33) did not match visual descriptions based on nerve origin of a type 1 SNC but met written definitions. These were termed type 1A1 and type 1A2. The SNC was asymmetrical in 57.69% (n = 120). The pooled mean length of the SN was 32.97 ± 14.12 cm (31.05-34.88), mean diameter was 2.31 ± 0.83 mm (2.20-2.42, and the distance of the posterior border of the lateral malleolus to the SN was found to be 1.72 ± 0.70 cm (1.63-1.80).

CONCLUSION

Anatomic variation in the SNC is highly variable, yet is consistent with previously observed literature. This study demonstrates two unaccounted formations of the SNC as well as two additional subcategories of SNC that were not included in the previous meta-analysis. These four variants warrant inclusion as standard formations of the SNC due to the high prevalence observed in this study as well as historical consistency observed in previous literature and case reports. These two SNC formations increase the risk of iatrogenic injury during surgical interventions of the lower extremity. Morphometric data describing the spatial relationship of this nerve complex on the posterolateral leg is consistent with previously reported data and aids in generating a large data set for future studies to characterize spatial properties of this nerve complex.

Critical Illness Neuropathy

Critical illness polyneuropathy (CIP) along with critical illness myopathy (CIM) is a frequent condition in critically ill patients. Similar to critical illness myopathy, the exact incidence, etiology, and mechanisms of CIP are not well understood. Although decreased compound muscle action potential amplitudes may be seen in both conditions, differentiation mostly relies on sensory nerve conduction studies which require special care to perform at intensive care units. In some instances, both CIP and critical illness myopathy are observed, and this condition is called critical illness neuromyopathy. In this review, nerve conduction studies and needle electromyography for the diagnosis of CIP and differentiation of CIP from critical illness myopathy and other conditions at intensive care units are summarized.

Communications between the superficial and deep fibular nerves in the foot: An anatomical and electrophysiological study

INTRODUCTION

The deep fibular sensory nerve can be recorded to evaluate for peripheral nerve injury; however, it can be challenging in some individuals. Anatomic variation could account for some of this difficulty. Cadaver dissection and electrophysiological testing were used to characterize deep and superficial fibular sensory nerve supply to the foot.

MATERIALS AND METHODS

Nineteen feet from 15 (8 males and 7 females) cadavers were dissected to identify the deep fibular nerves (DFNs) and superficial fibular nerves (SFNs). Sensation to the first dorsal web space was tested electrophysiologically in 101 participants (31 males and 70 females) with an age range of 18-47 years with stimulation over both DFNs and SFNs.

RESULTS

Eleven of the 19 (58%) cadaver limbs had a communication between SFNs and DFNs in the dorsum of the foot. A reliable sensory response was recorded in the first dorsal web space in 88% of the limbs tested. Deep fibular stimulation alone produced a response in 34% of the limbs, while superficial fibular stimulation alone produced a response in 10% of the limbs. A separate response with stimulation of both the DFNs and SFNs was recorded in 44% of the limbs.

CONCLUSIONS

A functional superficial to deep fibular sensory communication is present in a significant portion of the population. Those with the communication may not have the isolated sensory loss that would be expected in the first dorsal web space in conditions impacting the DFNs.

The utility of a point-of-care sural nerve conduction device for detection of diabetic polyneuropathy: A cross-sectional study

INTRODUCTION

Rapid and accessible methods for diagnosing diabetic polyneuropathy (DPN) have been developed, but not validated, in large cohorts of people with diabetes.

METHODS

The performance of a point-of-care device (POCD) was studied in 168 patients with type 2 diabetes, estimating the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) compared with conventional sural nerve conduction studies (NCS).

RESULTS

A POCD amplitude limit of 6 µV increased the sensitivity (96%) and NPV (98%), but decreased the specificity (71%) and PPV (54%) compared with the 4-µV limit, which had values of 78%, 92%, 89%, and 71%, respectively. POCD on both legs showed better performance than on 1 leg. POCD amplitudes and conduction velocities correlated significantly with conventional sural NCS, but POCD values were underestimated compared with NCS.

DISCUSSION

The POCD may be used as a suitable screening tool for detection of DPN. Patients with abnormal and borderline results should undergo conventional NCS. Muscle Nerve 59:187-193, 2019.

Diagnostic utility of distal nerve conduction studies and sural near-nerve needle recording in polyneuropathy

OBJECTIVE

The electrodiagnosis of polyneuropathy (PNP) may benefit from examination using near-nerve needle technique (NNT) and from inclusion of distal nerves. This study compared the diagnostic utility of distal nerve conduction studies (NCS) and NNT recording.

METHODS

Bilateral NNT and surface recording of the sural nerve and surface recording of the dorsal sural and medial plantar nerves were prospectively done in 91 patients with clinically suspected PNP. Distal NCS were additionally done in 37 healthy controls. Diagnostic reference standard was the final clinical diagnosis retrieved from the patients medical records after 1-4years.

RESULTS

The clinical follow-up diagnosis confirmed PNP in 68 patients. Equally high sensitivities of the dorsal sural (72%), medial plantar (75%), and sural nerve with NNT recording (77%) were seen, while the sensitivity of conventional surface recording of the sural nerve was lower (60%). Sural NCS with both NNT and surface recording and dorsal sural NCS showed high specificities (85-95%) and positive predictive values (94-98%), while a lower specificity was seen for the medial plantar nerve (68%).

CONCLUSION

NCS of distal nerves, especially the dorsal sural nerve, have high diagnostic power equalling sural NNT recording.

SIGNIFICANCE

The electrodiagnostic evaluation of patients with suspected PNP benefits from NCS of distal nerves.

Sural sensory nerve action potential: A study in healthy Indian subjects

BACKGROUND

The sural sensory nerve action potential (SNAP) is an important electrodiagnostic study for suspected peripheral neuropathies. Incorrect technique and unavailability of reference data can lead to erroneous conclusions.

OBJECTIVES

To establish reference data for sural SNAP in age-stratified healthy subjects at three sites of stimulation.

MATERIALS AND METHODS

A prospective study was conducted in 146 nerves from healthy subjects aged between 18 years and 90 years, stratified into six age groups (a = 18-30 years, b = 31-40 years, c = 41-50 years, d = 51-60 years, e = 61-70 years, and f >71 years). Sural SNAP was recorded antidromically, stimulating at three sites at distances of 14 cm, 12 cm, and 10 cm from the recording electrode. Mean - 2 standard deviation (SD) of the transformed data was used to generate reference values for amplitudes. Analysis of variance (ANOVA) test was used for inter-group and between three sites comparisons of amplitudes.

RESULTS

The lower limits of amplitude at 14 cm were 12.4 μV, 10.4 μV, 6.5 μV, 5.3 μV, 2.9 μV, and 1.9 μV; at 12 cm were 13.5 μV, 13.6 μV, 8.5 μV, 7.8 μV, 3.5 μV, and 2.8 μV; and at 10 cm were 16.3 μV, 16.3 μV, 11.1 μV, 10.0 μV, 4.8 μV, and 3.7 μV for groups a, b, c, d, e, and f, respectively. A statistically significant difference in amplitudes was noted from the three different sites of stimulation (P < 0.001). The amplitude differed significantly above the age of 60 years (P < 0.01) but not between groups e and f (P > 0.05).

CONCLUSION

This study provides reference data for sural SNAP in Indian population at three different sites of stimulation along the calf in six age groups. It also shows significant variation in amplitude from the three different sites of stimulation.