Can hyperthyroidism cause brain damage?

Hyperthyroidism, also known as overactive thyroid, is a condition in which the thyroid gland produces excess thyroid hormones. Thyroid hormones regulate many essential body functions, so too much of these hormones can significantly impact the body and brain.

Some of the key questions around hyperthyroidism and brain function include:

Does hyperthyroidism directly damage the brain?

What brain abnormalities are associated with hyperthyroidism?
Can hyperthyroidism cause cognitive impairment?
Are the effects reversible with treatment?

This article reviews the current evidence on the effects of hyperthyroidism on the brain and cognition.

Table of Contents

Can Hyperthyroidism Directly Damage the Brain?

Research suggests hyperthyroidism can cause certain brain abnormalities, but there is limited evidence that it directly damages brain tissue.

Some studies have found hyperthyroidism is associated with:

Cortical brain atrophy (shrinkage of the outer layer of the brain)
Enlargement of brain ventricles (fluid-filled spaces in the brain)
Generalized brain atrophy

However, these studies rely on imaging and have not proven hyperthyroidism actually destroys brain cells or tissues. The abnormalities may be reversible if thyroid levels are normalized.

So while hyperthyroidism may temporarily alter brain structure, direct damage is difficult to prove. More research is needed on the underlying mechanisms.

Main Brain Abnormalities Seen in Hyperthyroidism

Here are some of the main brain abnormalities associated with untreated hyperthyroidism:

Brain Abnormality	Description
Cortical atrophy	Thinning of the cerebral cortex, the outer layer of the brain involved in functions like memory, thinking and awareness.
Ventricular enlargement	Enlargement of the fluid-filled ventricles deep in the brain.
Cerebellar atrophy	Degeneration of the cerebellum, the part of the brain important for motor control and coordination.
White matter hyperintensities	Lesions in the white matter, the inner neural pathways of the brain.

These abnormalities are often detected through CT and MRI scans. Some may be reversible if thyroid levels are controlled.

Can Hyperthyroidism Impair Thinking and Memory?

In addition to structural changes, research indicates hyperthyroidism can also impair cognitive functions like memory, attention and concentration.

However, the evidence is mixed overall:

Some studies show hyperthyroid patients perform worse on cognitive tests, especially tasks involving mental speed and working memory.
Other studies find no significant difference in cognitive performance compared to healthy individuals.
The cognitive effects appear to be subtle overall.

Treatment to control thyroid levels often (but not always) improves symptoms.

In general, the cognitive impact is likely related to overactivity of thyroid hormones in certain brain regions. With treatment, these changes may be reversible.

Possible Mechanisms for Cognitive Changes

Here are some theorized mechanisms for how excess thyroid hormone could impair cognition:

Effects on neurotransmitters: Thyroid hormones influence levels of neurotransmitters like serotonin, dopamine and acetylcholine, which are essential for cognitive processes.
Cerebral blood flow changes: Hyperthyroidism increases blood flow to the brain, which can potentially cause hypoperfusion in certain regions.
Altered brain metabolism: Thyroid hormones accelerate brain glucose metabolism, which may impair neuronal activity.

Structural changes: Cortical atrophy and ventricular enlargement may affect memory, attention and other cognitive skills.

More research is needed to clarify the exact mechanisms. But it is likely a combination of factors driven by hyperactive thyroid hormones in the brain.

Can Hyperthyroidism Increase the Risk of Dementia?

Some studies suggest hyperthyroidism may raise the risk of certain forms of dementia, including:

Alzheimer’s disease: Some analyses have found an association, but the evidence has been mixed overall.
Vascular dementia: Several studies link hyperthyroidism to an increased risk of vascular dementia, likely related to blood vessel changes in the brain.

However, this is still an emerging area of research. More longitudinal studies tracking thyroid function and brain changes over time are needed.

It is possible excess thyroid hormone causes gradual brain changes that raise dementia risk later in life. But this link needs to be clarified by further research.

Can Treatment Reverse the Effects?

For most patients, the cognitive symptoms of hyperthyroidism can be reversed with treatment to normalize thyroid hormone levels.

However, recovery varies for different aspects:

Improvements in mood, anxiety, irritability and sleep often occur within weeks.
Cognitive symptoms like memory and concentration impairment may take several months to resolve.
Some studies show shortened attention span and mental slowing can persist long-term in some patients.

Structural changes like cortical atrophy may take 6-12 months to reverse.

So while many brain changes are reversible, it can take time for the brain to recover after thyroid levels are controlled. Adequate treatment and monitoring of cognition is important.

Mainstay Hyperthyroidism Treatments

Here are some of the main medical treatments for hyperthyroidism:

Antithyroid medications: Drugs like methimazole and propylthiouracil block thyroid hormone production.
Radioactive iodine: Damages the thyroid to reduce excess hormone production.
Surgery: Removes part or all of the thyroid gland if medications are ineffective.

Beta blockers: Used short-term to control symptoms like rapid heart rate.

Treatment is tailored to the individual based on factors like age, severity of hyperthyroidism, and other medical conditions.

Who is Most at Risk?

Research shows certain groups may be more vulnerable to brain changes with hyperthyroidism:

Older adults: Cognitive impairment and structural changes are more pronounced in older patients.
Patients with pre-existing cerebral atrophy: Those with prior cortical atrophy appear most susceptible to further damage.
Patients with longstanding hyperthyroidism: The risk increases with longer duration of elevated thyroid hormones.

Additionally, patients with more severe hyperthyroidism tend to experience more significant effects on the brain.

Takeaways

Here are some key summary points on hyperthyroidism and the brain:

Hyperthyroidism may cause reversible changes in brain structure, including cortical thinning, ventricular enlargement and cerebellar atrophy.

It can potentially impair cognition, especially attention, concentration, memory and mental speed.
The cognitive impact appears subtle in most cases, but may be more pronounced in older adults.
Treatment to normalize thyroid hormone levels will reverse most changes, but recovery can take months.

More research is still needed on whether hyperthyroidism increases long-term dementia risk.

In conclusion, untreated hyperthyroidism can negatively impact the brain. However, the effects are usually not severe or irreversible with proper treatment. Close monitoring of brain structure and cognitive function is important for hyperthyroid patients.

References

Bunevicius R, Prange AJ. Thyroid disease and mental disorders: cause and effect or only comorbidity? Curr Opin Psychiatry. 2010;23(4):363‐367.

Carvalho GA, Sanchez MN, Ward LS. The clinical use of thyroid function tests. Arq Bras Endocrinol Metabol. 2013;57(3):193‐204.
Chakraborty P, Bhattacharjee R, Chakraborty A, Kamal NM. Neuropsychiatric disorders in hyperthyroidism. Indian J Endocrinol Metab. 2017;21(4):673‐677.
Eskelinen SI, Vahlberg TJ, Isoaho RE, Kivelä SL, Irjala KM. Hyperthyroidism and dementia: a population-based study. Exp Clin Endocrinol Diabetes. 2007;115(10):586-90.

Guimarães JM, de Souza Lopes C, Baima J, Sichieri R. Depression symptoms and hypothyroidism in a population-based study of middle-aged Brazilian women. J Affect Disord. 2009;117(1-2):120‐123.
Kanaya AM, Harris F, Volpato S, Pérez-Stable EJ, Harris T, Bauer DC. Association between thyroid dysfunction and total cholesterol level in an older biracial population: the health, aging and body composition study. Arch Intern Med. 2002;162(7):773‐779.