Outcome and its predictors in Guillain–Barré syndrome

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Conduction block in acute motor axonal neuropathy

Guillain-Barré syndrome is divided into two major subtypes, acute inflammatory demyelinating polyneuropathy and acute motor axonal neuropathy. The characteristic electrophysiological features of acute motor axonal neuropathy are reduced amplitude or absence of distal compound muscle action potentials indicating axonal degeneration. In contrast, autopsy study results show early nodal changes in acute motor axonal neuropathy that may produce motor nerve conduction block. Because the presence of conduction block in acute motor axonal neuropathy has yet to be fully recognized, we reviewed how often conduction block occurred and how frequently it either reversed or was followed by axonal degeneration. Based on Ho's criteria, acute motor axonal neuropathy was electrodiagnosed in 18 patients, and repeated motor nerve conduction studies were carried out on their median and ulnar nerves. Forearm segments of these nerves and the across-elbow segments of the ulnar nerve were examined to evaluate conduction block based on the consensus criteria of the American Association of Electrodiagnostic Medicine. Twelve (67%) of the 18 patients with acute motor axonal neuropathy had definite (n = 7) or probable (n = 5) conduction blocks. Definite conduction block was detected for one patient (6%) in the forearm segments of both nerves and probable conduction block was detected for five patients (28%). Definite conduction block was present across the elbow segment of the ulnar nerve in seven patients (39%) and probable conduction block in two patients (11%). Conduction block was reversible in seven of 12 patients and was followed by axonal degeneration in six. All conduction blocks had disappeared or begun to resolve within three weeks with no electrophysiological evidence of remyelination. One patient showed both reversible conduction block and conduction block followed by axonal degeneration. Clinical features and anti-ganglioside antibody profiles were similar in the patients with (n = 12) and without (n = 6) conduction block as well as in those with (n = 7) and without (n = 5) reversible conduction block, indicating that both conditions form a continuum; a pathophysiological spectrum ranging from reversible conduction failure to axonal degeneration, possibly mediated by antibody attack on gangliosides at the axolemma of the nodes of Ranvier, indicating that reversible conduction block and conduction block followed by axonal degeneration and axonal degeneration without conduction block constitute continuous electrophysiological conditions in acute motor axonal neuropath

Capsular warning syndrome mimicking a jacksonian sensory march

A 57-year-old man, operated eight years before for a left frontal falx meningioma, presented with short lasting, stereotyped episodes of paresthesias ascending from the right foot to the hand. A diagnosis of somatosensory seizures with jacksonian march was made. The patient was given antiepilectics but 5 days later, a few hours after another paresthesic episodes, he developed right hemiplegia, hemianesthesia and dysartria due to an infarct of left capsular posterior limb. We deem that in this patient the paresthesic episodes were more likely an expression of a capsular warning syndrome than of parietal epilepsy because of the frontal localization of the surgical lesion, the absence of motor components in all episodes, the negativity of repeated EEG, and the lack of recurrences after stroke. In capsular warning syndrome sensory symptoms mimicking a jacksonian march can be due to ischemic depolarization progressively recruiting the somatotopically arranged sensory fibers in the posterior capsular limb

Optimizing the electrodiagnostic accuracy in Guillain-Barré syndrome subtypes: Criteria sets and sparse linear discriminant analysis

Objective To optimize the electrodiagnosis of Guillain-Barré syndrome (GBS) subtypes at first study. Methods The reference electrodiagnosis was obtained in 53 demyelinating and 45 axonal GBS patients on the basis of two serial studies and results of anti-ganglioside antibodies assay. We retrospectively employed sparse linear discriminant analysis (LDA), two existing electrodiagnostic criteria sets (Hadden et al., 1998; Rajabally et al., 2015) and one we propose that additionally evaluates duration of motor responses, sural sparing pattern and defines reversible conduction failure (RCF) in motor and sensory nerves at second study. Results At first study the misclassification error rates, compared to reference diagnoses, were: 15.3% for sparse LDA, 30% for our criteria, 45% for Rajabally's and 48% for Hadden's. Sparse LDA identified seven most powerful electrophysiological variables differentiating demyelinating and axonal subtypes and assigned to each patient the diagnostic probability of belonging to either subtype. At second study 46.6% of axonal GBS patients showed RCF in two motor and 8.8% in two sensory nerves. Conclusions Based on a single study, sparse LDA showed the highest diagnostic accuracy. RCF is present in a considerable percentage of axonal patients. Significance Sparse LDA, a supervised statistical method of classification, should be introduced in the electrodiagnostic practice

Un sistema a costo minimo per il miglioramento qualitativo del parlato

Questo lavoro propone una tecnica innovativa di beamforming adattativo per applicazioni di miglioramento qualitativo del parlato nell’ambito di comunicazioni viva voce. In particolare, viene provata l’efficacia della tecnica per una schiera “minima”, ovvero composta da soli due microfoni. Il contributo innovativo del sistema è apportato dall’algoritmo adattativo utilizzato, il variable step-size block exact affine projection algorithm (VSS-BEAPA), derivato dalla famiglia di algoritmi APA (affine projection algorithms), che si basa su un’elaborazione a blocchi e sull’utilizzo di un passo di adattamento variabile che permette di considerare scenari in cui la risposta impulsiva acustica viene sotto-modellata. La valutazione del sistema è condotta rispetto a diverse condizioni di lavoro e quindi rispetto a specifiche problematiche che possiamo così riassumere: presenza di rumore di fondo ambientale, presenza di sorgente interferente con il parlante, presenza di effetto eco dovuto al “ritorno di segnale” nella catena comunicativa. Le prestazioni sul miglioramento della qualità del segnale derivato dall’utilizzo del sistema proposto sono valutate attraverso la stima del rapporto segnale-rumore (SNR) e la stima oggettiva di un indice di intelligibilità. Gli esperimenti mostrano come il sistema proposto, pur non beneficiando di una schiera di sensori ottimale, riesca a produrre un sensibile decremento del livello di rumore interferente e un conseguente miglioramento qualitativo del segnale vocale

Architettura collaborativa per la cancellazione d'eco non lineare

La presenza di distorsioni prodotte da un altoparlante nel percorso d’eco si ripercuote sulle prestazioni di un cancellatore d’eco acustica (acoustic echo canceller, AEC) convenzionale. Conseguentemente, un degradamento della qualità del segnale vocale comporta una perdita di intelligibilità nella comunicazione viva-voce. Per evitare questo problema, vengono utilizzati cancellatori d’eco acustica non lineari (NAEC). In questo lavoro proponiamo un nuovo NAEC basato su una combinazione di due filtri, uno lineare ed uno non lineare, ciascuno dedicato ad un problema specifico. Il filtro lineare, dedicato esclusivamente alla stima del percorso d’eco, viene implementato tramite l’algoritmo variable step size improve proportionate normalized least mean square (VIP-NLMS), che ha la particolarità di prendere in considerazione la caratteristica di sparsità della risposta impulsiva acustica. Parallelamente al filtro lineare opera un filtro adattativo non lineare, dedicato alla modellazione delle distorsioni presenti nel percorso d’eco, e basato sulla tecnica dei functional link. L’architettura proposta inoltre prevede la combinazione convessa dei due filtri, migliorando le prestazioni del cancellatore prescindere dal livello di distorsione presente nel percorso d’eco. I risultati sperimentali mostrano l’efficacia del cancellatore non lineare proposto rispetto ad AEC convenzionali

Guillain-Barré and Miller Fisher syndromes--new diagnostic classification.

Guillain-Barré syndrome (GBS) and its variant, Miller Fisher syndrome (MFS), exist as several clinical subtypes with different neurological features and presentations. Although the typical clinical features of GBS and MFS are well recognized, current classification systems do not comprehensively describe the full spectrum of either syndrome. In this Perspectives article, GBS and MFS are classified on the basis of current understanding of the common pathophysiological profiles of each disease phenotype. GBS is subclassified into classic and localized forms (for example, pharyngeal-cervical-brachial weakness and bifacial weakness with paraesthesias), and MFS is divided into incomplete (for example, acute ophthalmoparesis, acute ataxic neuropathy) and CNS subtypes (Bickerstaff brainstem encephalitis). Diagnostic criteria based on clinical characteristics are suggested for each condition. We believe this approach to be more inclusive than existing systems, and argue that it could facilitate early clinical diagnosis and initiation of appropriate immunotherapy