key: cord-0933214-9d4eace6 authors: Bocci, Tommaso; Bulfamante, Gaetano; Campiglio, Laura; Coppola, Silvia; Falleni, Monica; Chiumello, Davide; Priori, Alberto title: Brainstem clinical and neurophysiological involvement in COVID-19 date: 2021-03-18 journal: J Neurol DOI: 10.1007/s00415-021-10474-0 sha: b8e279468f3109aee1bc3c48f4f29f0670b75e60 doc_id: 933214 cord_uid: 9d4eace6 nan the first is mediated by a disynaptic pathway between the sensory nucleus of the trigeminal nerve (V) in the mid pons and the ipsilateral facial nucleus in the lower pontine tegmentum. The second response (RII) originates through a multi-synaptic circuit in the medulla oblongata [9] . The supraorbital nerve was stimulated through a pair of silver chloride cup electrodes with the cathode over the supraorbital foramen and the anode 2 cm above (constant current stimulation, pulse width 200 µs, inter-trial interval ranging between 25 and 35 s to avoid habituation) [4, 9] . A total of 8 blink reflexes were recorded on each side and data were collected from superimposed traces. Electromyographic signal was captured by surface electrodes and analyzed (band-pass 10 Hz-10 kHz, sampling rate 5 kHz, sensitivity set 200 µV/ Div; sweep speed 10 ms/Div). Neurophysiological responses in COVID-19 patients were compared with those from 15 age-matched healthy volunteers and 5 non-COVID ICU intubated patients (Fig. 1) . The glabellar and corneal reflexes were also clinically tested; the response to both reflexes was labeled as normal (score = 2), reduced (1) or absent (0). At the time of evaluation, patients were awake and in the 60 min before none of them assumed drugs interfering with neuromuscular transmission or depressing the central nervous system. Whereas all the COVID-19 patients had normal pontine RI latencies (p = 0.1), in two of them the RII was absent and in the remaining cases markedly abnormal, both the ipsilateral (latency: p < 0.0001; amplitude: p < 0.0001; duration: p < 0.0001) and the contralateral response (latency: p = 0.0014; amplitude: p < 0.0001; duration: p < 0.0001; see Table 1 ). Among COVID-19 patients, four had an absent glabellar reflex (score = 0), while the others had a markedly impaired reflex (score = 1). The corneal reflex was present in eight COVID-19 patients out of 11, and reduced in the remaining three. Non-COVID patients showed normal glabellar and corneal reflexes. Our findings provide the neurophysiological and clinical evidence of SARS-Cov-2-related brainstem involvement in Our results agree with recent histopathological data showing a preferential involvement of the lower medulla, without any evidence of intracerebral bleeding or small-vessels thromboses, and confirming the intraneuronal localization of SARS-Cov-2 nucleoprotein [13] . Although SARS-Cov-2-related Guillain-Barré syndrome has been recently reported, mainly of axonal type and with an early involvement of the cranial nerves [16] , normal RI latencies and amplitudes rule out this diagnosis in our patients. Note that, whereas RI latencies did not differ among groups, both RII latencies and duration (ipsilateral and contralateral) were significantly prolonged in COVID-19 patients. The bulbar RII amplitude was significantly decreased in COVID-19 group. Histograms are mean values, error bars are standard deviation. In the neurophysiological assessment, parametric analyses were used, as all datasets passed the Shapiro-Wilk test for normality (p > 0.05). A one-way repeated measures ANOVA was used to compare neurophysiological data among groups (healthy volunteers, COVID-19 and other ICU patients) and the Bonferroni method served as post-hoc comparison (statistical significance set at p < 0.017; ***p < 0.0001; **p < 0.01) From a clinical perspective, the glabellar reflex was impaired more than the corneal. The two reflexes rely on slightly different circuits, targeting the pontine sensory nucleus and the nucleus of the spinal tract of the trigeminal nerve, then projecting to the facial nucleus and reticular formation (RF). However, the amount of fibers reaching the interneuronal network of the medullary reticular formation is lower for the corneal than for the glabellar reflex, probably accounting for the differences we observed [9] . Overall, our results suggest that the brainstem involvement likely contributes to respiratory failure in COVID-19 patients as postulated by Manganelli [12] and Baig [3] . Yet, BR assesses a ponto-medullary circuitry partly involving the reticular formation [9] close to the respiratory nuclei. The reticular formation itself modulates the activity of the respiratory centers [10] . Funding The Authors declare no funding source. The corresponding author has full access to data and has the right to publish such data. Data will be available upon reasonable request to the corresponding author. Conflicts of interest None of the authors have no conflict of interest to report. The study was approved by the institutional review board and the ethics committee at "Azienda Socio-Sanitaria Territoriale Santi Paolo e Carlo". The study has been performed in accordance with the ethical standards laid down in the Declaration of Helsinki. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http:// creat iveco mmons. org/ licen ses/ by/4. 0/. Severe neurologic syndrome associated with Middle East respiratory syndrome corona virus (MERS-CoV) Neuroinvasion by human respiratory coronaviruses Evidence of the COVID-19 virus targeting the CNS: tissue distribution, host-virus interaction, and proposed neurotropic mechanisms The orbicularis oculi reflexes. The international federation of clinical neurophysiology Brain invasion by mouse hepatitis virus depends on impairment of tight junctions and beta interferon production in brain microvascular endothelial cells First ultrastructural autoptic findings of SARS-Cov-2 in olfactory pathways and brainstem Neuroinvasive and neurotropic human respiratory coronaviruses: potential neurovirulent agents in humans Axonal transport enables neuron-to-neuron propagation of human coronavirus OC43 A neurophysiological approach to brainstem reflexes. Blink reflex Respiratory rhythm generation and pattern formation: oscillators and network mechanisms The neuroinvasive potential of SARS-CoV2 may play a role in the respiratory failure of COVID-19 patients Servillo G (2020) Brainstem involvement and respiratory failure in COVID-19 Neuropathology of patients with COVID-19 in Germany: a post-mortem case series The Many Faces of Covid-19 at a Glance: A University Hospital Multidisciplinary Account From COVID-19: what if the brain had a role in causing the deaths Guillain-Barre syndrome associated with SARS-CoV-2