Mehdi J. Van Den Bos

Description:Objective: There is a need for improved diagnostic tools in Amyotrophic Lateral Sclerosis (ALS). Our objective was to assess muscle ultrasound as a diagnostic tool in patients with ALS and determine a simplified screening protocol to aid implementation in clinical practice. Methods: Ultrasound of bulbar and limb muscles was prospectively performed on all patients referred to a single centre with suspected ALS. Clinical measures of disease severity and upper motor neuron impairment were also recorded. Receiver operating characteristic (ROC) curves were calculated to assess the diagnostic utility of muscle ultrasound. Results: 94 patients initially suspected of ALS were recruited to this observational cohort study. Forty-four were subsequently diagnosed as ALS and 50 as disease mimics. ALS patients demonstrated a higher frequency and more generalised distribution of fasciculations compared to mimics. A simplified 5 muscle screening protocol exhibited an AUC of 0.94 (95 %CI 0.89-0.99) in discriminating ALS from mimics. The presence of ≥ 3 fasciculating muscles detected using this screening protocol was 89 % sensitive and 88 % specific for the diagnosis of ALS. Conclusions: Muscle ultrasound, screening as few as 5 muscles, has diagnostic utility in ALS. Conclusions: Muscle ultrasound enhances clinical diagnosis in ALS.

Description:Objective: Far field potentials (FFP) have been proposed as a reliable neurophysiological prognostic biomarker in amyotrophic lateral sclerosis (ALS). This study evaluates the diagnostic utility of ulnar nerve FFP in ALS. Methods: Comprehensive peripheral neurophysiological assessments were conducted in 62 ALS and 43 ALS-mimicking disorder participants. The ulnar nerve was stimulated at the wrist, recording motor responses over the abductor digit minimi (ADM) muscle. Conventional compound muscle action potentials (CMAP), FFP, and near field potential amplitudes were recorded, alongside the split-hand index, neurophysiological index, motor unit number estimation (MScanFit-MUNE), and motor unit index (MUNIX). Diagnostic utility was evaluated using receiver operating characteristic (ROC) analysis. Results: In ALS, FFP amplitude was significantly lower (5.07 ± 0.36 mV) compared to ALS mimics (8.25 ± 0.40 mV, p < 0.001). FFP amplitude exhibited a moderate-to-strong correlation with neurophysiological biomarkers, including CMAP amplitude (ρ = 0.77, p < 0.001), split-hand index (ρ = 0.53, p < 0.001), neurophysiological index (ρ = 0.52, p < 0.001), MUNIX (ρ = 0.69, p < 0.001), and MScanFit-MUNE (ρ = 0.66, p < 0.001). Weak-to-moderate correlations were also observed with clinical measures of disease progression, including upper limb muscle strength, ALS functional rating score-revised (ALSFRS-R) and the rate of decline in the ALSFRS-R fine motor subscore. ROC analysis demonstrated that FFP amplitude reliably distinguished ALS from mimicking disorders (AUC = 0.80, 95% CI: 0.71-0.89), with consistent diagnostic accuracy across ALS phenotypes. Conclusions: The diagnostic capability of FFP amplitude was comparable to established neurophysiological biomarkers utilized in ALS. It is a promising prognostic and diagnostic biomarker for ALS. Its simplicity and reproducibility complement traditional neurophysiological measures, offering potential for clinical application in ALS diagnosis and monitoring.

Description:Objective: Threshold tracking transcranial magnetic stimulation (TMS) has exhibited utility as a diagnostic technique in Amyotrophic Lateral Sclerosis (ALS). Different threshold tracking paradigms have recently been proposed. The present study assessed the diagnostic utility of serial ascending and parallel threshold tracking TMS in ALS. Methods: Threshold tracking TMS was undertaken on 90 prospectively recruited participants suspected of ALS. Short interval intracortical inhibition (SICI) was recorded with serial ascending and parallel threshold tracking paradigms between Interstimulus Interval (ISI) 1-to-7 ms. The primary outcome measure was differences in diagnostic utility of the paradigms in differentiating ALS from ALS mimicking disorders using receiver operating characteristic (ROC) analysis (DeLong statistical method). Results: Reduction in SICI reliably differentiated ALS from mimic disorders, irrespective of the threshold tracking paradigm. Comparison of area under the curve (AUC) established a significantly higher value for mean SICI (1-7 ms) with the serial ascending SICI paradigm (0.81, 95 % confidence interval 0.72-0.91) compared to the parallel paradigm (SICI 0.72, 95 % confidence interval 0.61-0.83, p = 0.0065). The better diagnostic utility of serial ascending paradigm was evident for SICI recorded between 1-to-5 ms, and was maintained irrespective of disease onset site, degree of functional impairment, and the degree of lower motor neuron dysfunction. A comparable diagnostic utility across threshold tracking paradigms was evident in ALS participants who presented with a relative paucity of upper motor neuron signs. Conclusions: While threshold tracking TMS reliably differentiated ALS from mimic disorders, the present study established better diagnostic utility with the serial ascending threshold tracking TMS paradigm. Conclusions: The serial ascending threshold tracking TMS should be used in a clinical setting as a diagnostic tool for ALS.

Description:Background: Cortical hyperexcitability is an early feature of amyotrophic lateral sclerosis (ALS), linked to dysfunction in inhibitory and facilitatory cortical circuits, measurable using paired-pulse transcranial magnetic stimulation (TMS). Short-interval intracortical inhibition (SICI) is a robust biomarker of inhibitory function and an ALS diagnostic marker. Short interval intracortical facilitation (SICF) serves as a biomarker of facilitatory function, while the index of excitation assesses the contribution of these circuits to hyperexcitability. This study aimed to evaluate the diagnostic effectiveness of SICF and the index of excitation in distinguishing ALS from non-ALS mimic disorders. Methods: This cross-sectional study assessed cortical excitability in participants with suspected ALS from two Sydney centres, classified using the Gold Coast criteria. Threshold tracking TMS measured SICI, SICF, and the index of excitation. Diagnostic performance was evaluated using receiver operating characteristic (ROC) analysis, with sensitivity, specificity, and optimal cut-off values determined. Results: Of 154 participants, 95 were diagnosed with ALS and 48 with non-ALS mimics. SICI demonstrated a marginally higher diagnostic accuracy (AUC 0.84, 95% CI:0.77-0.89) compared to SICF (AUC 0.77, 95% CI:0.68-0.84, p = 0.028). The index of excitation showed comparable accuracy to SICI (AUC 0.82, 95% CI: 0.75-0.88, p = 0.328). The optimal SICF cut-off (≤ -13.6%) provided 70.5% sensitivity and 70.8% specificity, while the index of excitation cut-off (≥ 64.5%) yielded 71.6% sensitivity and 70.8% specificity. Conclusions: The present study established modest diagnostic potential of increased SICF and index of excitation in differential ALS from mimic disorders, thereby enhancing understanding of the role of inhibitory and facilitatory cortical circuits in ALS diagnosis.

Description:Upper motor neuron (UMN) dysfunction is an important feature of amyotrophic lateral sclerosis (ALS) for the diagnosis and understanding of pathogenesis. The identification of UMN signs forms the basis of ALS diagnosis, although may be difficult to discern, especially in the setting of severe muscle weakness. Transcranial magnetic stimulation (TMS) techniques have yielded objective physiological biomarkers of UMN dysfunction in ALS, enabling the interrogation of cortical and subcortical neuronal networks with diagnostic, pathophysiological, and prognostic implications. Transcranial magnetic stimulation techniques have provided pertinent pathogenic insights and yielded novel diagnostic and prognostic biomarkers. Cortical hyperexcitability, as heralded by a reduction in short interval intracortical inhibition (SICI) and an increase in short interval intracortical facilitation (SICF), has been associated with lower motor neuron degeneration, patterns of disease evolution, as well as the development of specific ALS clinical features including the split hand phenomenon. Reduction in SICI has also emerged as a potential diagnostic aid in ALS. More recently, physiological distinct inhibitory and facilitatory cortical interneuronal circuits have been identified, which have been shown to contribute to ALS pathogenesis. The triple stimulation technique (TST) was shown to enhance the diagnostic utility of conventional TMS measures in detecting UMN dysfunction. Resting-state EEG is a novel neurophysiological technique developed for directly interrogating cortical neuronal networks in ALS, that have yielded potentially useful physiological biomarkers of UMN dysfunction. The present review discusses physiological biomarkers of UMN dysfunction in ALS, encompassing conventional and novel TMS techniques developed to interrogate the functional integrity of the corticomotoneuronal system, focusing on pathogenic, diagnostic, and prognostic utility.