Further insight on A-wave in acute and chronic demyelinating neuropathies

European Academy of Neurology/Peripheral Nerve Society Guideline on diagnosis and treatment of Guillain-Barré syndrome

Guillain-Barré syndrome (GBS) is an acute polyradiculoneuropathy. Symptoms may vary greatly in presentation and severity. Besides weakness and sensory disturbances, patients may have cranial nerve involvement, respiratory insufficiency, autonomic dysfunction and pain. To develop an evidence-based guideline for the diagnosis and treatment of GBS, using Grading of Recommendations, Assessment, Development and Evaluation (GRADE) methodology a Task Force (TF) of the European Academy of Neurology (EAN) and the Peripheral Nerve Society (PNS) constructed 14 Population/Intervention/Comparison/Outcome questions (PICOs) covering diagnosis, treatment and prognosis of GBS, which guided the literature search. Data were extracted and summarised in GRADE Summaries of Findings (for treatment PICOs) or Evidence Tables (for diagnostic and prognostic PICOs). Statements were prepared according to GRADE Evidence-to-Decision (EtD) frameworks. For the six intervention PICOs, evidence-based recommendations are made. For other PICOs, good practice points (GPPs) are formulated. For diagnosis, the principal GPPs are: GBS is more likely if there is a history of recent diarrhoea or respiratory infection; CSF examination is valuable, particularly when the diagnosis is less certain; electrodiagnostic testing is advised to support the diagnosis; testing for anti-ganglioside antibodies is of limited clinical value in most patients with typical motor-sensory GBS, but anti-GQ1b antibody testing should be considered when Miller Fisher syndrome (MFS) is suspected; nodal-paranodal antibodies should be tested when autoimmune nodopathy is suspected; MRI or ultrasound imaging should be considered in atypical cases; and changing the diagnosis to acute-onset chronic inflammatory demyelinating polyradiculoneuropathy (A-CIDP) should be considered if progression continues after 8 weeks from onset, which occurs in around 5% of patients initially diagnosed with GBS. For treatment, the TF recommends intravenous immunoglobulin (IVIg) 0.4 g/kg for 5 days, in patients within 2 weeks (GPP also within 2-4 weeks) after onset of weakness if unable to walk unaided, or a course of plasma exchange (PE) 12-15 L in four to five exchanges over 1-2 weeks, in patients within 4 weeks after onset of weakness if unable to walk unaided. The TF recommends against a second IVIg course in GBS patients with a poor prognosis; recommends against using oral corticosteroids, and weakly recommends against using IV corticosteroids; does not recommend PE followed immediately by IVIg; weakly recommends gabapentinoids, tricyclic antidepressants or carbamazepine for treatment of pain; does not recommend a specific treatment for fatigue. To estimate the prognosis of individual patients, the TF advises using the modified Erasmus GBS outcome score (mEGOS) to assess outcome, and the modified Erasmus GBS Respiratory Insufficiency Score (mEGRIS) to assess the risk of requiring artificial ventilation. Based on the PICOs, available literature and additional discussions, we provide flow charts to assist making clinical decisions on diagnosis, treatment and the need for intensive care unit admission.

European Academy of Neurology/Peripheral Nerve Society Guideline on diagnosis and treatment of Guillain-Barré syndrome

Guillain-Barré syndrome (GBS) is an acute polyradiculoneuropathy. Symptoms may vary greatly in presentation and severity. Besides weakness and sensory disturbances, patients may have cranial nerve involvement, respiratory insufficiency, autonomic dysfunction and pain. To develop an evidence-based guideline for the diagnosis and treatment of GBS, using Grading of Recommendations, Assessment, Development and Evaluation (GRADE) methodology, a Task Force (TF) of the European Academy of Neurology (EAN) and the Peripheral Nerve Society (PNS) constructed 14 Population/Intervention/Comparison/Outcome questions (PICOs) covering diagnosis, treatment and prognosis of GBS, which guided the literature search. Data were extracted and summarised in GRADE Summaries of Findings (for treatment PICOs) or Evidence Tables (for diagnostic and prognostic PICOs). Statements were prepared according to GRADE Evidence-to-Decision (EtD) frameworks. For the six intervention PICOs, evidence-based recommendations are made. For other PICOs, good practice points (GPPs) are formulated. For diagnosis, the principal GPPs are: GBS is more likely if there is a history of recent diarrhoea or respiratory infection; CSF examination is valuable, particularly when the diagnosis is less certain; electrodiagnostic testing is advised to support the diagnosis; testing for anti-ganglioside antibodies is of limited clinical value in most patients with typical motor-sensory GBS, but anti-GQ1b antibody testing should be considered when Miller Fisher syndrome (MFS) is suspected; nodal-paranodal antibodies should be tested when autoimmune nodopathy is suspected; MRI or ultrasound imaging should be considered in atypical cases; and changing the diagnosis to acute-onset chronic inflammatory demyelinating polyradiculoneuropathy (A-CIDP) should be considered if progression continues after 8 weeks from onset, which occurs in around 5% of patients initially diagnosed with GBS. For treatment, the TF recommends intravenous immunoglobulin (IVIg) 0.4 g/kg for 5 days, in patients within 2 weeks (GPP also within 2-4 weeks) after onset of weakness if unable to walk unaided, or a course of plasma exchange (PE) 12-15 L in four to five exchanges over 1-2 weeks, in patients within 4 weeks after onset of weakness if unable to walk unaided. The TF recommends against a second IVIg course in GBS patients with a poor prognosis; recommends against using oral corticosteroids, and weakly recommends against using IV corticosteroids; does not recommend PE followed immediately by IVIg; weakly recommends gabapentinoids, tricyclic antidepressants or carbamazepine for treatment of pain; does not recommend a specific treatment for fatigue. To estimate the prognosis of individual patients, the TF advises using the modified Erasmus GBS outcome score (mEGOS) to assess outcome, and the modified Erasmus GBS Respiratory Insufficiency Score (mEGRIS) to assess the risk of requiring artificial ventilation. Based on the PICOs, available literature and additional discussions, we provide flow charts to assist making clinical decisions on diagnosis, treatment and the need for intensive care unit admission.

Identical late motor responses in early Guillain-Barré syndrome: A-waves and repeater F-waves

Electrodiagnostic (EDx) studies play a key role in the investigation of suspected Guillain-Barré syndrome (GBS), providing diagnostic and prognostic information. However, initial EDx findings may not fulfill the neurophysiological criteria for the disease. The aim of this study was to estimate the occurrence and characteristics of A-waves and repeaters F-waves (Freps), both late motor responses identical in latency and configuration, in early stages of GBS. We retrospectively analyzed the initial nerve conduction study (NCS) of 26 GBS patients performed within 10 days from symptom onset. The final subtype diagnosis was acute inflammatory demyelinating polyneuropathy (AIDP) in 16 patients (six met the criteria at the initial EDx study and 10 at follow-up) and acute motor axonal neuropathy (AMAN) in 10 patients (six initially). Identical late responses were commonly found in the majority of nerves (84%). A-waves were present in 59% and an increased frequency of Freps was calculated in 61% of the 105 studied nerves. A-waves morphology (single or complex) could not distinguish between AIDP and AMAN. Nerves with normal NCS had a significantly higher frequency of A-waves, either isolated or in combination with increased index total Freps, as compared to nerves with low compound muscle action potential (CMAP) amplitudes or conduction block. Our findings suggest that both late responses can be useful as early markers of conduction changes of various pathophysiology, being frequently present even prior to abnormalities of CMAP parameters.

Significance of A-waves in Isolated Calf Pain as a Manifestation of Radicular Pain During F-wave Studies: A Case Report

Although isolated lower leg pain (LPP) without neurological deficit is frequently encountered in clinical practice, some of its aspects remain underexplored in the literature. There is contrasting evidence supporting the use of late responses, namely, F-waves and A-waves, in the assessment of nerve root damage. We describe the case of a 29-year-old female who presented with pain in the left calf. Neurological investigations were only significant for a positive straight leg raise test on the left side. F-wave studies of the left tibial nerve at distal and proximal points of stimulation showed the presence of the A-wave preceding the F-wave, the duration of which was prolonged. One year later, the patient reported new-onset left-sided low back pain with radiation to the gluteal area that appeared after a 10-hour airplane flight. Low back and calf pain were resolved with manipulative therapy. A-waves that had been recorded before F-waves were now no longer detectable. The presence of a neuropathic radicular component was accompanied by subclinical damage to motor fibers, as detected by routine F-waves studies. This case report illustrates the utility of integrating F-wave duration and the presence of A-waves into clinical, neurophysiological, and neuroimaging data in determining pain-generating structures in isolated LLP.

A-waves are associated with neuropathic pain in leprosy

INTRODUCTION/AIMS

The A-wave is a late response related either to demyelination or early axonal regeneration. It may be helpful in the evaluation of some peripheral neuropathies. In leprosy, previous studies suggested that A-waves could be a neurophysiological marker of pain in patients during reactions. Herein we have attempted to further assess the profile and clinical correlates of A-waves by exploring a large leprosy cohort.

METHODS

Between 2015 and 2018, 63 patients with leprosy (47 men and 16 women) had A-waves in nerve conduction studies and were included in this study. We included patients regardless of whether they were experiencing leprosy reactions or not. We then compared clinical features in nerves with and without A-waves.

RESULTS

The mean age of study participants was 46.5 ± 12.3 years and most had borderline leprosy. From this cohort, we assessed separately 83 motor nerves that demonstrated A-waves (group A⁺ ) and 29 motor nerves that did not demonstrate A-waves (group A^- ). Neuropathic pain (NP) was found in 66 of 83 nerves in group A⁺ , but only 5 of 29 in group A^- (79.5 vs 17.2%, P < .001). In contrast, no significant between-group difference emerged regarding presence of reactions, sensory function (based on Semmes-Weinstein evaluations), or muscle strength. A-waves were found in nerves with neuropathic pain experiencing (39 of 66 = 59%) or not experiencing (27 of 66 = 41%) leprosy reactions.

DISCUSSION

These results show that A-waves are associated with neuropathic pain in leprosy patients, regardless of the nerves affected and the immune status (in reaction or not).

The Physiological Significance of A-Waves in Early Diabetic Neuropathy: Assessment of Motor Nerve Fibers by Neurophysiological Techniques

Objective: This study aimed to investigate how early A-waves could occur in type II diabetes, and what it implied functionally. Methods: We performed conduction velocity distribution (CVD) test in peroneal nerves of 37 type II diabetic patients with normal nerve conduction study (NCS) and 22 age-matched controls. The electrophysiological data and clinical information were analyzed. Results: A-waves were observed in 45.9% of diabetic patients and only in 1 person in healthy controls, all detected in the tibial nerves. The diabetic patients with A-waves showed faster conduction velocity in all quartiles in the motor peroneal nerves compared to the patients without A-waves, and their CVD histograms were shifted to the right side, consisting of a significantly larger percentage of fast conducting fibers. There was no significant difference in the CVD values of the upper extremity nerves among the patients with and without A-waves and the healthy controls. Conclusion: A-waves could occur in type II diabetes as early as when NCS showed normal, and represented as a sign of neuropathy as well as a sign of rescued motor nerve function.

Characteristics of A-waves in patients with amyotrophic lateral sclerosis (ALS) versus demyelinating neuropathies (DN)

Objective

Detect the occurrence and characteristics of A-waves in amyotrophic lateral sclerosis (ALS) and demyelinating neuropathies (DN).

Methodology

Nerve conduction studies (NCS) of 28 patients (14 patients with ALS and 14 patients with DN) were reanalyzed to look for A-waves.

Results

We studied 61 nerves of the ALS group and 64 nerves of DN. In the ALS group, A-waves were detected in 21 nerves out of 61 nerves (34.4%). In the DN group, A-waves were recorded from 25 nerves out of 64 nerves (39%). In the DN group, A-waves were detected more often in nerves of upper extremities than lower extremities (out of a total of 25 nerves with A-waves, 18 median and ulnar nerves showed A-waves (72%) and that was statistically significant (P = 0.0021)). Complex A-waves (CAWs) occurred exclusively in patients with DN.

Conclusion

Most of the A-waves in the DN group were recorded more frequently from nerves of the upper extremities than those from lower extremities. CAWs occurred only in DN.

Significance

CAW seems to be a useful specific electrodiagnostic tool to distinguish DN from ALS.

A waves in electroneurography: differential diagnosis with other late responses

Neurographic studies are an extension of clinical examination and are performed for the functional assessment of peripheral nerves. The study of motor and sensory conduction velocity and the presence, amplitude, morphology and symmetry of the response to electrical stimulation are crucial for the diagnosis and management of peripheral neuromuscular disorders. Neurography also plays an important role in the search for so-called late responses comprising the F wave, H reflex, axonal response and A wave. By analysing the parameters of each late wave, this paper addresses the pathophysiological features and the most common conditions impairing the physiology of late responses, with a special focus on A waves.

Clinical Significance of A Waves in Acute Inflammatory Demyelinating Polyradiculoneuropathy

PURPOSE

A wave is a late response recognized during recording of F waves. Though they might be seen in healthy subjects, their presence assumes significance in a patient presenting with polyradiculoneuropathy.

METHODS

In this prospective study, 75 patients with acute inflammatory demyelinating polyradiculoneuropathy (AIDP) were enrolled. They were divided into two groups based on the presence or absence of A waves. Clinical features, electrophysiological parameters and extent of clinical recovery in short-term follow-up were analyzed.

RESULTS

A waves were present in 49 out of 75 patients (65%). Most common pattern observed was multiple A waves. Prevalence of A waves was more in lower limb nerves than upper limb nerves. Occurrence of A waves correlated with the presence of conduction block. Patients with A waves had higher Hughes grade (P = 0.003) and lower Medical Research Council sum score at 6 weeks of follow-up (P = 0.04) as compared to patients without A waves.

CONCLUSIONS

A waves are common in acute inflammatory demyelinating polyradiculoneuropathy form of Guillain Barre syndrome and are considered as a marker of demyelination. Long-term follow-up studies are required to ascertain their significance in prognostication and assessing recovery.

A Retrospective Study of the Characteristics and Clinical Significance of A-Waves in Amyotrophic Lateral Sclerosis

A-wave was observed in patients with motor neuron disease (1). However, data on the characteristics and clinical significance of A-waves in patients with amyotrophic lateral sclerosis (ALS) have been scarce. The F-wave studies of 83 patients with ALS and 63 normal participants which were conducted previously at the Department of Neurology in Peking Union Medical College Hospital were retrospectively reviewed to determine the occurrence of A-waves in ALS. A-waves occurred more frequently in ALS patients than in normal controls. For the median and peroneal nerves, the frequencies of nerves with A-waves and frequencies of patients with A-waves were comparable between the ALS patients and normal controls. For the ulnar and tibial nerves, the frequencies of nerves with A-waves and frequencies of patients with A-waves were significantly increased in the ALS patients compared with those of the normal participants. Disease progression rate was slower in the ALS patients with A-waves (0.73 ± 0.99) than that in the ALS patients without A-waves (0.87 ± 0.55, P = 0.007). No correlations were found between the amplitudes of F-waves with A-waves and those of A-waves in the ulnar nerves (r = 0.423, P = 0.149). No correlations were found between the persistence of F-waves with A-waves and the persistence of A-waves in the ulnar nerves as well (r = 0.219, P = 0.473). The occurrence of A-waves may indicate dysfunction of lower motor neurons and possibly imply a relatively slower degenerative process.

Diagnostic accuracy of neurophysiological criteria for early diagnosis of AIDP: A prospective study

OBJECTIVE

To assess the diagnostic accuracy of electrodiagnostic (EDX) criteria for the early detection and characterization of Guillain-Barré syndrome (GBS) in clinical practice.

METHODS

We conducted a prospective study in patients referred for an EDX exam with clinical suspicion of GBS. We evaluated four sets of neurophysiological criteria and four neurophysiological tests among those recently proposed for the early diagnosis of GBS.

RESULTS

We recruited 84 patients. Acute inflammatory demyelinating polyneuropathy (AIDP) was the final diagnosis in 23 patients. No axonal forms were found. The best sensitivity was obtained using Rajabally et al.'s criteria (82.1%), whereas the specificity was 90.0% for Ho et al.'s and Hadden et al.'s criteria and 100% for the Dutch GBS study group and Rajabally's criteria. Regarding the neurophysiological tests proposed for early diagnosis, the sensitivity ranged from 16.6 to 100%, whereas specificity ranged from 73.1 to 98.3%.

CONCLUSION

The Dutch GBS study group and Rajabally et al.'s criteria showed an optimal combination of sensitivity and specificity for clinical practice, although with a slightly higher sensitivity for Rajabally et al.'s criteria. None of the neurophysiological parameters recently proposed for early diagnosis have good diagnostic accuracy for clinical application.

SIGNIFICANCE

In a real clinical setting with patients referred by neurologists and emergency doctors, an EDX study performed within a week of symptom onset supports the diagnosis of AIDP in 82% of cases.

Bochum ultrasound score versus clinical and electrophysiological parameters in distinguishing acute-onset chronic from acute inflammatory demyelinating polyneuropathy

INTRODUCTION

The aim of this study was to evaluate whether a nerve ultrasound score (Bochum ultrasound score, BUS), clinical, and electrophysiological parameters could distinguish subacute chronic (CIDP) from acute inflammatory demyelinating polyneuropathy (AIDP).

METHODS

Phase 1: The charts of 35 patients with polyradiculoneuropathy were evaluated retrospectively regarding BUS, clinical, and electrophysiological parameters (A-waves, sural nerve sparing pattern, sensory ratio>1). Phase 2: All parameters were evaluated prospectively in 10 patients with subacute polyradiculoneuropathy.

RESULTS

Phase 1: A sum score of ≥2 points in BUS and the presence of sensory symptoms were significantly more frequent in the subacute CIDP group than in the AIDP group (P<0.001).The electrophysiological parameters showed no significant changes between the 2 groups. Phase 2: BUS (83.3%; 100%;), sensory symptoms (100%; 75%), absence of autonomic nervous system dysfunction (83.3%; 75%), or bulbar palsy (83.3%; 50%) showed the best sensitivity and specificity in distinguishing subacute CIDP from AIDP.

CONCLUSIONS

BUS is a useful diagnostic tool for distinguishing subacute CIDP from AIDP.