Loss of smell, confusion, strokes: Does Covid-19 target the nervous system?


Reports of patients with neurological symptoms have emerged during the pandemic. Scientists don’t yet know whether these are a direct effect of the virus or part of the body’s response to infection.

For many people, a sudden loss of smell is the first sign that something’s wrong. “One gentleman said he realized it with hand sanitizer,” says Carol Yan, a rhinologist at the University of California, San Diego. “All of a sudden it was like water to him.” The loss of smell, or anosmia, is such a common symptom of Covid-19 that the US Centers for Disease Control and Prevention recently added it to its official list.

The loss of smell (or taste) is one of many emerging hints that the SARS-CoV-2 virus may affect the nervous system. Physicians around the world have documented neurological symptoms in a significant fraction of Covid-19 patients. Some patients have experienced headaches, dizziness and other relatively minor symptoms, while others have had more serious problems like confusion and impaired movement, and even seizures and strokes.

Such reports have been circulating on message boards used by physicians, and they are just now making their way into the peer-reviewed scientific literature. Nobody knows at this point how widespread neurological symptoms are, nor the extent to which they contribute to the overall clinical picture for Covid-19.

Another huge unknown is whether SARS-CoV-2 can attack the nervous system directly by infecting neurons — as rabies and a number of other viruses do — or cause neurological symptoms indirectly, by triggering rampant inflammation or blood clotting

These are critical questions, says Samuel Pleasure, a neuroscientist and neurologist at the University of California, San Francisco. For a small number of patients, neurological symptoms seem to be the earliest or even the only indicator of infection. For others, lingering or post-infection neurological problems could complicate recovery. “We don’t know whether or not that’s going to be the case yet, but it’s an important unanswered question,” says Pleasure.

No-smell test

Reports of lost taste and smell — often in the absence of the kind of nasal congestion that interferes with olfaction with the common cold — have been circulating for months. In one of the first peer-reviewed journal articles on the subject, Yan and colleagues describe results from an online survey of 262 patients in the UCSD hospital system. Slightly more than two-thirds of those who tested positive for Covid-19 experienced taste and smell deficits.

The deficits weren’t subtle, Yan says. “Most people went from like a ten to zero.” Fortunately, as patients get better, they seem to be regaining their sensory abilities, usually within a few weeks, the team reported April 12 in the International Forum of Allergy & Rhinology

In an April 22 letter to the Journal of the American Medical Association, physicians reported a similar prevalence of anosmia in Covid-19–positive patients at a regional hospital in Treviso, Italy. For 12 percent of these patients, the loss of smell occurred prior to other symptoms. For 3 percent, it was the only symptom they ever experienced.

Such reports have prompted several medical associations for ear, nose and throat specialists to issue statements urging physicians to consider anosmia as a [ … ]

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