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Introduction: The aim of the study is to determine the role of upper motor neuron (UMN) or lower motor neuron (LMN) dysfunction as the primary initiator of distal-proximal and lateral-medial gradients of muscle involvement in amyotrophic lateral sclerosis (ALS)., Methods: Concentric needle electromyography recordings were performed in deltoid, abductor digiti minimi, and first dorsal interosseous (FDI) muscles in patients with ALS and controls during slight voluntary contraction needed to activate two motor units (MU). Five motor unit potential (MUP) pairs were recorded from each muscle. Motor unit potential analyses were performed offline using Multi-MUP analysis program. Quantitative MUP parameters, MU firing rate (FR), FR variability (FRV), and mean consecutive difference (MCD) were calculated. Motor-evoked potentials and the triple stimulation technique (TST) were performed to evaluate UMN involvement., Results: Twenty patients with ALS along with 20 age and sex-matched healthy volunteers were enrolled. Quantitative MUP parameters compatible with denervation and reinnervation were found in patients with ALS, who also showed higher FR, FRV, and MCD values, most prominently in FDI. First dorsal interosseous FRV was lower in patients with abnormal central motor conduction time (CMCT). Firing rate and FRV were negatively correlated with CMCT, but not with TST., Conclusion: Distal limb muscles, particularly FDI, revealed more prominent FR abnormalities in patients with ALS in parallel with the distal-proximal and lateral-medial gradients of the selective muscle involvement pattern which seems predominantly to be correlated with LMN dysfunction. Reduced FRV may be associated with the presence of UMN dysfunction in ALS., Competing Interests: Conflict of Interest: The authors declared that there is no conflict of interest., (Copyright: © 2024 Turkish Neuropsychiatric Society.)

Some respiratory viruses have long been known to cause neurological involvement. A novel coronavirus, leading to severe acute respiratory syndrome, also called coronavirus disease 19 (COVID-19), seems to be a new member of neuroinvasive viruses. While severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) keeps on spreading around the world rapidly, reports about the neurological manifestations associated with SARS-CoV-2, increases day by day. It is reported that a variety of symptoms and syndromes such as headache, dizziness, confusion, ataxia, epilepsy, ischemic stroke, neuropathic pain and myopathy are common especially in more severe COVID-19 patients. It is also suggested that the development of neurological complications is strongly associated with a poor outcome. On the other hand, hyposmia can be the unique symptom in COVID-19 carriers and this can serve as a marker for identifying the otherwise asymptomatically infected patients. It is thought that SARS-CoV-2 may cause neurological symptoms through direct or indirect mechanisms. Nevertheless, neuroinvasion capability of SARS-CoV2 is confirmed by the presence of the virus, in the cerebrospinal fluid of a COVID-19 patient with encephalitis, and this is proven by gene sequencing. In conclusion, during the COVID-19 pandemic, it is crucial to be aware of the possible neurological complications of the disease. Therefore, in this review, we aimed to report neurological manifestations associated with SARS-CoV-2 and possible underlying pathophysiological mechanisms. Due to the high homology of SARS-CoV-2 with other human coronaviruses such as SARS-CoV or Middle East Respiratory Syndrome (MERS)-CoV, reviewing the neurological involvement also associated with these coronaviruses will provide an idea about the long-term complications of COVID-19., Competing Interests: Conflicts of interest: There were no conflicts of interest in this study., (Copyright: © 2020 Turkish Neuropsychiatric Society.)