Long COVID has a long list of symptoms – and a lesser-known but troubling one is the feeling of having internal shaking, often with no outward signs of it. In a new Long COVID study conducted at Yale, over a third of participants report this strange symptom that feels like shaking. inside their bodies.
This is no small thing. These are people who are suffering greatly and this symptom contributes in part to their suffering.
Harlan Krumholz, MD, SM
Long COVID remains one of the least understood aspects of the SARS-CoV-2 pandemic. Shortly after the pandemic began in 2020, health experts had to come to terms with the fact that some patients who survive their first COVID-19 infection never fully recover. People with Long COVID have developed a variety of symptoms ranging from gastrointestinal problems to chronic fatigue.
Now researchers at the Yale School of Medicine have added this symptom to the list. According to their study, a subgroup of people with Long COVID appear to develop “internal tremors” – a twitching or vibrating sensation that is not visible to the naked eye and is not associated with physical spasms. The study was published on July 26 in the American Journal of Medicine.
“Many patients (with this symptom) were turned away because doctors had never heard of it – and many patients wondered if anyone else had experienced it,” says Harlan Krumholz MD, SM, Harold H. Hines Jr. Professor of Medicine at Yale School of Medicine (YSM) and director of the Yale New Haven Hospital Center for Outcomes Research and Evaluation. Krumholz hopes this study “makes people feel less alone.”
When COVID became a persistent disease
Krumholz and his research team focus on cardiovascular disease, but during the pandemic, they used their skills to fight SARS-CoV-2. As Long COVID became established as a persistent health problem for many people, Krumholz and his team, in collaboration with immunologist Akiko Iwasaki, PhD, Sterling Professor of Immunobiology at Yale School of Medicine, turned their attention to Long COVID. While speaking to patients with Long COVID, they noticed that some of them mentioned what he calls a “very unusual syndrome.”
“They felt as if their muscles were shaking,” he says, or as if “their nerves were vibrating” just beneath their skin.
Neurological diseases such as Parkinson’s can cause tremors. However, according to Krumholz, in long-COVID patients who complained of this symptom, there was no noticeable tremor, nor were any spasms detectable under the skin. Krumholz had never heard of such a thing before. In fact, the team’s research found fewer than 10 other scientific studies that described something similar, says Dr. Tianna Zhou, a first-year resident at Brigham and Women’s Hospital in Boston who worked on the project as a student at Yale School of Medicine and is lead author of the current study.
The fact that the symptom was novel and largely invisible helped Krumholz explain why doctors largely ignored it when their patients brought it up.
To find out how widespread internal tremors really are, Krumholz and Iwasaki and their teams surveyed 423 members of a Yale-based Long COVID research group about their health and life experiences. All participants had contracted COVID-19 between May 2022 and June 2023.
Internal tremors are a disturbing symptom
A total of 37% – 158 survey participants – said they had experienced internal tremors. That’s a surprising number because “it’s not a symptom that’s commonly reported,” says Zhou. Sensations ranged from annoying to unbearable, with “most people just finding it extremely bothersome,” says Krumholz. Interestingly, the 158 people with internal tremors were in poorer health overall, more financially burdened, and more likely to struggle with housing insecurity than long-COVID patients without tremors.
Even though the feeling is usually not visible to others, “it’s not trivial,” says Krumholz. “These are people who are suffering significantly, and part of what contributes to their suffering is this symptom.”
The survey found that people with internal tremors were more likely to report nervous system disorders, as well as symptoms such as dizziness and heart rate problems, as part of their long-COVID experience. However, what lies behind the feeling is still unknown.
Despite the umbrella term used for it, Long COVID is “not really a disease,” says Krumholz. Internal tremors can indicate one of the subtypes of the condition, which may have implications for treatment. Krumholz hopes that identifying the different symptoms of Long COVID will help researchers pinpoint the causes and determine a wide range of therapies for patients who are still experiencing the effects of the virus and whose lives have been severely disrupted by it.
