What's Behind Brain Fog in Treated Hypothyroidism?

Miriam E. Tucker

June 08, 2021

The phenomenon of brain fog, as described by some patients with hypothyroidism despite treatment, is often associated with fatigue and cognitive symptoms and may be relieved by a variety of pharmacologic and nonpharmacologic approaches, new research suggests.

The findings come from a survey of more than 700 patients with hypothyroidism due to thyroid surgery and/or radioactive iodine therapy (RAI) or Hashimoto's, who reported having brain fog.

The survey results were presented May 29 at the American Association of Clinical Endocrinology (AACE) Virtual Annual Meeting 2021 by investigators Matthew D. Ettleson, MD, and Ava Raine, of the University of Chicago, Illinois.

Many patients with hypothyroidism continue to experience symptoms despite taking thyroid hormone replacement therapy and having normal thyroid function test results.

These symptoms can include quantifiable cognitive, quality of life, and metabolic abnormalities. However, "some patients also experience vague and difficult to quantify symptoms, which they describe as brain fog," Raine said.

The brain fog phenomenon has been described with somewhat varying features in several different chronic conditions, including postural orthostatic tachycardia syndrome, myalgic encephalomyelitis/chronic fatigue syndrome, fibromyalgia, post-menopausal syndrome, and recently, among people with "long haul" COVID-19 symptoms.

However, brain fog associated with treated hypothyroidism has not been explored in-depth, despite the fact that patients often report it, Raine noted.

Results Will Help Clinicians Assist Patients With Brain Fog

Fatigue was the most prominent brain fog symptom reported in the survey, followed by forgetfulness and difficulty focusing. On the other hand, rest and relaxation were the most reported factors that alleviated symptoms, followed by thyroid hormone adjustment.

"Hopefully these findings will help clinicians to recognize and treat the symptoms of brain fog and shed light on a condition which up until now has not been very well understood," Ettleson said.

Asked to comment, session moderator Jad G. Sfeir, MD, of the Mayo Clinic, Rochester, Minnesota, told Medscape Medical News: "We do see patients complain a lot about this brain fog. The question is how can I help, and what has worked for them in the past?"

"When you have symptoms that are vague, like brain fog, you don't have a lot of objective tools to [measure] so you can't really develop a study to see how a certain medication affects the symptoms. Relying on subjective information from patients saying what worked for them and what did not, you can draw a lot of implications to clinical practice."

The survey results, Sfeir said, "will help direct clinicians to know what type of questions to ask patients based on the survey responses and how to make some recommendations that may help."

Fatigue, Memory Problems, Difficulty Focusing Characterize Brain Fog

The online survey was distributed to hypothyroidism support groups and through the American Thyroid Association. Of the 5282 respondents with hypothyroidism and symptoms of brain fog, 46% (2453) reported having experienced brain fog symptoms prior to their diagnosis of hypothyroidism.

The population analyzed for the study was the 17% (731) who reported experiencing brain fog weeks to months following a diagnosis of hypothyroidism. Of those, 33% had Hashimoto's, 21% thyroid surgery, 11% RAI therapy, and 15.6% had both thyroid surgery and RAI.  

Brain fog symptoms were reported as occurring "frequently" by 44.5% and "all the time" by 37.0%. The composite symptom score was 22.9 out of 30.

Fatigue, or lack of energy, was the most commonly named symptom, reported by over 90% of both the thyroid surgery/RAI and Hashimoto's groups, and as occurring "all the time" by about half in each group. Others reported by at least half of both groups included memory problems, difficulty focusing, sleep problems, and difficulties with decision-making. Other symptoms frequently cited included confusion, mood disturbance, and anxiety.

"Each...domain was reported with some frequency by at least 85% of respondents, regardless of etiology of hypothyroidism, so it really was a high symptom burden that we were seeing, even in those whose symptoms were the least frequent," Raine noted.

Symptom scores generally correlated with patient satisfaction scores, particularly with those of cognitive signs and difficulty focusing.

Lifting the Fog: What Do Patients Say Helps Them?

The survey asked patients what factors improved or worsened their brain fog symptoms. By far, the most frequent answer was rest/relaxation, endorsed by 58.5%. Another 10.5% listed exercise/outdoor time, but 1.5% said exercise worsened their symptoms.

Unspecified adjustments of thyroid medications were said to improve symptoms for 13.9%. Specific thyroid hormones reported to improve symptoms were liothyronine in 8.8%, desiccated thyroid extract in 3.1%, and levothyroxine in 2.7%. However, another 4.2% said thyroxine worsened their symptoms.

Healthy/nutritious diets were reported to improve symptoms by 6.3%, while consuming gluten, a high-sugar diet, and consuming alcohol were reported to worsen symptoms for 1.3%, 3.2%, and 1.3%, respectively. Caffeine was said to help for 3.1% and to harm by 0.6%.

Small numbers of patients reported improvements in symptoms with vitamins B12 and D, Adderall, or other stimulant medications, antidepressants, naltrexone, sun exposure, and blood glucose stability.

Other factors reported to worsen symptoms included menstruation, infection or other acute illness, pain, and "loud noise."   

Ettleson pointed out, "For many of these patients [the brain fog] may have nothing to do with their thyroid. We saw a large proportion of patients who said they had symptoms well before they were ever diagnosed with hypothyroidism, and yet many patients have linked these brain fog symptoms to their thyroid."

Nonetheless, he said, "I think it's imperative for the clinician to at least engage in these conversations and not just stop when the thyroid function tests are normal. We have many lifestyle suggestions that have emerged from this study that I think physicians can put forward to patients who are dealing with this...early in the process in addition to thyroid hormone adjustment, which may help some patients."  

Ettleson, Raine, and Sfeir have reported no relevant financial relationships.

AACE Virtual Annual Meeting 2021. Abstract 1000765. Presented May 29, 2021.

Miriam E. Tucker is a freelance journalist based in the Washington, DC, area. She is a regular contributor to Medscape, with other work appearing in The Washington Post, NPR's Shots blog, and Diabetes Forecast magazine. She is on Twitter: @MiriamETucker.

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