To the Editor: Neurologic symptoms, including headache, altered mental status, and anosmia, occur in many patients with Covid-19. [1][2][3] We report the neuropathological findings from autopsies of 18 consecutive patients with SARS-CoV-2 infection who died in a single teaching hospital between April 14 and April 29, 2020.All the patients had nasopharyngeal swab samples that were positive for SARS-CoV-2 on qualitative reverse-transcriptase-polymerase-chainreaction (RT-PCR) assays. The median age was 62 years (interquartile range, 53 to 75), and 14 patients (78%) were men. The presenting neurologic symptoms were myalgia (in 3 patients), headache (in 2), and decreased taste (in 1). Coexisting conditions included diabetes mellitus (in 12 patients), hypertension (in 11), cardiovascular disease (in 5), hyperlipidemia (in 5), chronic kidney disease (in 4), prior stroke (in 4), dementia (in 4), and treated anaplastic astrocytoma (in 1) (see Tables S1 and S2 in the Supplementary Appendix, available with the full text of this letter at NEJM.org).The patients had presented a median of 2 days (interquartile range, 0 to 5) after the onset of the first symptoms of SARS-CoV-2 infection and were hospitalized for a median of 6 days (interquartile range, 2 to 9) before death (Fig. S1A); 11 received mechanical ventilation. According to a retrospective chart review by neurologists, all the patients had a confusional state or decreased arousal from sedation for ventilation. Brain magnetic resonance imaging, electroencephalographic imaging, and cerebrospinal fluid examinations were not performed. Cranial computed tomography without contrast was performed in 3 patients and showed no acute abnormalities; the tumor resection cavity in the patient with a known anaplastic astrocytoma was seen.Death occurred 0 to 32 days after the onset of symptoms (median, 8 days; mean, 10 days). Autopsies were performed in a uniform manner with sampling of 10 standard brain areas. Specimens were fixed in formalin and stained with hema-

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Objective:To explore the spectrum of skeletal muscle and nerve pathology of patients who died following SARS-CoV-2 infection and assess for direct viral invasion of these tissues.Methods:Psoas muscle and femoral nerve sampled from 35 consecutive autopsies of patients who died following SARS-CoV-2 infection and 10 SARS-CoV-2-negative controls were examined under light microscopy. Clinical and laboratory data were obtained by chart review.Results:In SARS-CoV-2-positive patients, mean age at death was 67.8 years (range 43-96 years) and the duration of symptom onset to death ranged from 1-49 days. Four patients had neuromuscular symptoms. Peak creatine kinase was elevated in 74% (mean 959 U/L, range 29-8413 U/L). Muscle showed type 2 atrophy in 32 patients, necrotizing myopathy in 9, and myositis in 7. Neuritis was seen in 9. Major histocompatibility complex-1 (MHC-1) expression was observed in all cases of necrotizing myopathy and myositis and 8 additional patients. Abnormal expression of myxovirus resistance protein A (MxA) was present on capillaries in muscle in 9 patients and in nerve in 7. SARS-CoV-2 immunohistochemistry was negative in muscle and nerve in all patients. In the 10 controls, muscle showed type 2 atrophy in all patients, necrotic muscle fibers in 1, MHC-1 expression in non-necrotic/non-regenerating fibers in 3, MxA expression on capillaries in 2, and inflammatory cells in none, and nerves showed no inflammatory cells or MxA expression.Conclusion:Muscle and nerve tissue demonstrated inflammatory/immune-mediated damage likely related to release of cytokines. There was no evidence of direct SARS-CoV-2 invasion of these tissues.Classification of evidence:This study provides class IV evidence that muscle and nerve biopsies document a variety of pathological changes in patients dying with COVID-19.

Protease inhibitors were independent predictors of cerebrospinal fluid (CSF) escape in antiretroviral therapy (ART)–experienced human immunodeficiency virus–infected adults. M184V/I combined with thymidine analog mutations were more frequent in adults with CSF escape compared to no escape. These findings suggest optimizing ART may reduce likelihood of CSF escape.

One approach for developing targeted stroke therapies is to identify the neuronal protective and destructive signaling pathways and gene expression that follow ischemic insult. In some neural injury models, the transforming growth factor-beta family member activin can provide neuroprotective effects in vivo and promote neuronal survival. This study tests if activin supports cortical neurons after ischemic challenge in vitro and if signals after cerebral ischemia involve activin in vivo. In a defined cell culture model that uses hydrogen peroxide (H2O2)-free radical stress, activin addition maintained neuronal survival. H2O2 treatment increased activin mRNA twofold in surviving cortical neurons, and inhibition of activin with neutralizing antibodies caused neuronal death. These data identify activin gene changes as a rapid response to oxidative stress, and indicate that endogenous activin acts as a protective factor for cortical neurons in vitro. Similarly, after transient focal cerebral ischemia in adult mice, activin mRNA increased at 1 and 4 h ipsilateral to the infarct but returned to control values at 24 h after reperfusion. Intracellular activated smad signals were detected in neurons adjacent to the infarct. Activin was also increased after 2 h of 11% hypoxia. Activin mRNA increased at 1 h but not 4 or 24 h after hypoxia, similar to the time course of erythropoietin and vascular endothelial growth factor induction. These findings identify activin as an early-regulated gene response to transient ischemia and hypoxia, and its function in cortical neuron survival during oxidative challenge provides a basis to test activin as a potential therapeutic in stroke injury.

Objective The purpose of this study was to describe cerebrovascular, neuropathic, and autonomic features of post‐acute sequelae of coronavirus disease 2019 ((COVID‐19) PASC). Methods This retrospective study evaluated consecutive patients with chronic fatigue, brain fog, and orthostatic intolerance consistent with PASC. Controls included patients with postural tachycardia syndrome (POTS) and healthy participants. Analyzed data included surveys and autonomic (Valsalva maneuver, deep breathing, sudomotor, and tilt tests), cerebrovascular (cerebral blood flow velocity [CBFv] monitoring in middle cerebral artery), respiratory (capnography monitoring), and neuropathic (skin biopsies for assessment of small fiber neuropathy) testing and inflammatory/autoimmune markers. Results Nine patients with PASC were evaluated 0.8 ± 0.3 years after a mild COVID‐19 infection, and were treated as home observations. Autonomic, pain, brain fog, fatigue, and dyspnea surveys were abnormal in PASC and POTS (n = 10), compared with controls (n = 15). Tilt table test reproduced the majority of PASC symptoms. Orthostatic CBFv declined in PASC (−20.0 ± 13.4%) and POTS (−20.3 ± 15.1%), compared with controls (−3.0 ± 7.5%, p = 0.001) and was independent of end‐tidal carbon dioxide in PASC, but caused by hyperventilation in POTS. Reduced orthostatic CBFv in PASC included both subjects without (n = 6) and with (n = 3) orthostatic tachycardia. Dysautonomia was frequent (100% in both PASC and POTS) but was milder in PASC (p = 0.002). PASC and POTS cohorts diverged in frequency of small fiber neuropathy (89% vs 60%) but not in inflammatory markers (67% vs 70%). Supine and orthostatic hypocapnia was observed in PASC. Interpretation PASC following mild COVID‐19 infection is associated with multisystem involvement including: (1) cerebrovascular dysregulation with persistent cerebral arteriolar vasoconstriction; (2) small fiber neuropathy and related dysautonomia; (3) respiratory dysregulation; and (4) chronic inflammation. ANN NEUROL 2022;91:367–379

We evaluated the incidence, distribution, and histopathologic correlates of microvascular brain lesions in patients with severe COVID-19. Sixteen consecutive patients admitted to the intensive care unit with severe COVID-19 undergoing brain MRI for evaluation of coma or neurologic deficits were retrospectively identified. Eleven patients had punctate susceptibility-weighted imaging (SWI) lesions in the subcortical and deep white matter, eight patients had >10 SWI lesions, and four patients had lesions involving the corpus callosum. The distribution of SWI lesions was similar to that seen in patients with hypoxic respiratory failure, sepsis, and disseminated intravascular coagulation. Brain autopsy in one patient revealed that SWI lesions corresponded to widespread microvascular injury, characterized by perivascular and parenchymal petechial hemorrhages and microscopic ischemic lesions. Collectively, these radiologic and histopathologic findings add to growing evidence that patients with severe COVID-19 are at risk for multifocal microvascular hemorrhagic and ischemic lesions in the subcortical and deep white matter.

Post-infectious anosmias typically follow death of olfactory sensory neurons (OSNs) with a months-long recovery phase associated with parosmias. While profound anosmia is the leading symptom associated with COVID-19 infection, many patients regain olfactory function within days to weeks without distortions. Here, we demonstrate that sterile induction of anti-viral type I interferon signaling in the mouse olfactory epithelium is associated with diminished odor discrimination and reduced odor-evoked local field potentials. RNA levels of all class I, class II, and TAAR odorant receptors are markedly reduced in OSNs in a non-cell autonomous manner. We find that people infected with COVID-19 rate odors with lower intensities and have odor discrimination deficits relative to people that tested negative for COVID-19. Taken together, we propose that inflammatory-mediated loss of odorant receptor expression with preserved circuit integrity accounts for the profound anosmia and rapid recovery of olfactory function without parosmias caused by COVID-19.