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|Year : 2021 | Volume
| Issue : 2 | Page : 376-377
Sequential Nerve Conduction Studies in Guillain-Barre Syndrome: Is it Worth the Efforts?
Madhu Nagappa, Arun B Taly
National Institute of Mental Health and Neurosciences, Bangalore, Karnataka, India
|Date of Submission||22-Mar-2021|
|Date of Decision||22-Mar-2021|
|Date of Acceptance||22-Mar-2021|
|Date of Web Publication||24-Apr-2021|
Arun B Taly
National Institute of Mental Health and Neurosciences, Institute of National Importance, Bangalore - 560 029, Karnataka
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Nagappa M, Taly AB. Sequential Nerve Conduction Studies in Guillain-Barre Syndrome: Is it Worth the Efforts?. Neurol India 2021;69:376-7
Only a few disorders have sustained the attention of neurologists and neuroscientists for longer than a century as Guillain Barre Syndrome (GBS). Scientific work has focussed on understanding the pathobiology, establishing and refining the diagnostic criteria, variants and subtypes, treatment, and prognostic markers, among others., During the past forty years, a number of electrophysiological criteria have been proposed to support the diagnosis and cross-sectionally subtype GBS as acute inflammatory demyelinating polyneuropathy (AIDP) or axonal (acute motor axonal neuropathy-AMAN, acute motor-sensory axonal neuropathy- AMSAN). The proportion of patients having AIDP and axonal subtypes has varied depending upon the set(s) of the criteria used by different authors and the geographical location of the study, with a substantial number, also falling in the “equivocal” category., Most of these observations about subtyping have been based on a single nerve conduction study (NCS).
Clinical and electrophysiological mismatch in GBS has called for understanding the distinction between transient “axonal failure” (good outcome) and “primary or secondary axonal degeneration” (poor outcome). A critical review of observations on serial NCS resulted in the recognition of “temporal dispersion” as an important marker for AIDP/demyelination, and “reversible conduction failure” as an explanation for the early and unexpected clinical/electrophysiological recovery in the so-called axonal subtype. The inherent limitations of the electrophysiological criteria, as well as the time required to identify the true pathology by NCS, were acknowledged. Thus, diverse views emerged about the role of NCS in correct subtyping: a “second” study is necessary vs a “single” study with robust criteria may be enough.,,
Mani and Alexander, in this issue of Neurology India, report their observations on serial NCS in 31 patients of GBS carried out at a mean interval of 1.9 weeks (range: 1 to 6 weeks). They used three prevailing electrodiagnostic criteria and noted that during the first study
45.2% to 71% met the criteria for AIDP, while 29% to 54.8% of patients were classified as axonal GBS. In the second study, 41.9% to 64.5% met the criteria for AIDP, while 29% to 58.1% of patients were classified as axonal. The change in the electrophysiological subtypes ranged from 9.6% to 16.1%, based on the criteria used. The shift, like in other studies, occurred across both the subtypes, i.e., axonal to demyelinating and vice versa. They also found that the abnormalities in facial and phrenic nerve conduction, and blink reflex, as well as “sural sparing”, were more frequent in AIDP when the criteria of Rajabally et al. were used but not when Hadden's criteria were applied. They also observed a trend in detecting ganglioside antibodies in serum in patients having the axonal subtype. The authors believe that serial NCS may have therapeutic and prognostic significance.
This is perhaps the first study from India to report the implications of serial NCS in reclassifying the patients as AIDP or axonal. The authors need to be complemented considering the practical difficulties in carrying out serial NCS in GBS. However, similar to earlier publications their study is limited by its retrospective design, a small number of patients, the variable and overlapping interval between the serial NCS, use of different criteria and cut-offs, confounding effect of treatment on nerve conduction parameters, and lack of clinical correlates to appreciate the impact of the 'revision' in the subtyping on the treatment and outcome.,, Besides it is also important to be aware of the possible contribution of variations in inter-and intra-rater observations during serial recording.
GBS is dynamic in its clinical course and so are the nerve conduction parameters. In the initial stage of the disease, the conduction abnormalities may be minimal and restricted to only some segments. Serial conduction studies show changes as the disease evolves or resolves but may not necessarily correlate with the clinical state or outcome. There is a need to have a “gold standard” or at least consensus on the NCS parameters (number of nerves and segments to be assessed, defining reversible conduction failure and inclusion of sensory conduction parameters and electromyography), cut-offs for categorising as axonal or AIDP, and timing of the serial NCS to precisely subtype GBS. A single NCS may not help in precise prognostication or choose the treatment early in the course when it is required. Serial NCS help us to understand the variable course of the disease, consider alternate therapeutic options if it alters the subtype, and accurate prognostication.
Electrophysiological abnormalities are the after-effects of the immunological events that govern the pathological alterations in the nerves. Efforts are being made to find reliable biomarkers early in the course of the disease (serum and CSF neurofilament light chain for axonal damage, sphingomyelin for demyelination, and ganglioside complex antibodies), and explore imaging modalities and machine learning technology for correct subtyping.,,
In summary, electrophysiological studies are essential in understanding the dynamic nature of GBS and find its subtypes. The timing of the study and the sets of criteria used to achieve the precision lack of agreement among the experts. To settle the debate and for better understanding the theranostic significance of serial nerve conduction studies, it is desirable to carry out a prospective study, have a large cohort, use “consensus/standardized electrodiagnostic criteria” and document clinical correlates of electrophysiological observations.
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