Estimates aren’t evidence
The Swanson/Volkow commentary contains a lot of references to “might, could, and may,” said Dr. Coghill. While it’s true that COVID-19 could produce a novel etiologic subtype of ADHD, “the point here is at the moment, all of this is based on hypotheses,” he said.
The Spanish flu did produce mental health consequences – survivors reported depression, sleep disturbances, mental distraction, dizziness, and difficulties coping at work. In the United States, flu death rates from 1918 to 1920 were directly attributed to suicide rates. Unfortunately, these impacts weren’t widely researched, said Dr. Coghill.
It also seems clear that the 1918 Spanish flu outbreak was associated with significant neurological consequences, said Dr. Coghill. By 1919 and 1920, physicians and researchers in the United Kingdom were reporting increases in a variety of symptoms among some patients recovering from flu, such as neuropathy, neurasthenia, meningitis, degenerative changes in nerve cells, and a decline in visual acuity.
The EL cases Dr. Swanson mentioned did coincide with and reach epidemic proportions alongside the Spanish flu. “But still, a causal relationship is far from proven,” said Dr. Coghill.
Sol Levy, MD, described a “disease of criminals” following the 1918 pandemic, in which patients exhibited a high degree of general hyperkinesis, a difficulty in maintaining quiet attitudes, abruptness and clumsiness, and “explosive motor release of all voluntarily inhibited activities.”
However, these impairments suggest a much broader presentation typically seen in ADHD, noted Dr. Coghill.
Neurological complications occur more commonly than initially thought in severe COVID-19, with estimates ranging from 36% to 84%. But in a systematic review of neuropsychiatric complications of severe coronavirus infection, researchers found few psychiatric sequelae of these infections. While they did mention impaired concentration and difficulties with emotional ability, it’s very important to remember that these conditions “are cardinal symptoms of a wide range of psychiatric disorders,” said Dr. Coghill.
Overall, more neurological and neuropsychiatric symptoms largely confine to those with severe COVID-19, meaning they’re much less likely to occur in children and young adults, he said.
If there are severe effects of COVID-19, Dr. Swanson countered that “they might have more ADHD than the complex residual effects [Dr. Coghill] described. I hope that he’s right, but I do think there will be biological co-effects of COVID-19 that will produce symptoms that are more ADHD than other neurological disorders.”
Epigenetic effects
Researchers are now seeing transgenerational and intergenerational effects of potential infection. “So I certainly back high-quality studies looking at the effects of maternal and paternal infection on offspring,” said Dr. Coghill. Establishing clinical cohort studies to follow up on this population would be essential in understanding the risks of SARS-CoV-2. “That might be one way we’ll see an increase in ADHD,” said Dr. Coghill.
The reality is COVID-19 hasn’t been around for that long, and current knowledge about it is limited, he said. Rapid publications, cross-sectional or retrospective data, and poor methodological quality and rigor make generalizability difficult. In addition, limited testing and detection probably underestimate prevalence of neurological and neuropsychiatric complications.
“If history teaches us anything, it is that we should always be measured in how we glean lessons from the past. So let’s not get ahead of ourselves,” he cautioned.
An informal, post-discussion survey of session participants revealed that a slight majority – 55%-60% – expected residual effects of COVID-19 to lead to more ADHD, compared to 40%-45% who didn’t think this would happen.
Dr. Swanson has two patents: (PIXA4), which uses a “time-of-flight” camera to measure growth on infants, and a provisional patent on the mechanism of tolerance to stimulant medication (PATSMTA). Dr. Coghill worked for several pharmaceutical companies but had no disclosures relevant to this debate.