Hashimoto's encephalopathy (HE) is a rare, serious condition that impacts brain function. It is thought to be connected to autoimmune thyroid conditions, particularly Hashimoto's thyroiditis, although the precise cause remains unclear. HE can produce a range of neurological symptoms such as confusion, seizures, and even dementia-like states. Fortunately, in most cases, these symptoms can be managed and often reversed with appropriate treatment.

HE is estimated to affect roughly two out of every 100,000 individuals. Despite its rarity, experts believe it may be underdiagnosed due to its subtle onset and overlap with more common neurological disorders. Most individuals diagnosed are between the ages of 40 and 55, and women are disproportionately affected—being diagnosed four times more often than men. While HE can occur in children, this is believed to be very uncommon.

Some experts suggest renaming HE to "steroid-responsive encephalopathy associated with autoimmune thyroiditis" (SREAT), as many people diagnosed with HE do not exhibit the classic signs of Hashimoto's thyroiditis.

Common Symptoms of HE

HE typically presents as a decline in cognitive function. The condition can follow three distinct courses:

  1. Relapsing-remitting: Individuals experience episodes that come and go. These episodes may include seizures or stroke-like events.

  2. Progressive: The symptoms develop and worsen gradually, sometimes leading to dementia, hallucinations, or disturbances in consciousness.

  3. Self-limiting: Symptoms may occur for a limited time and then resolve without intervention.

Across these different courses, some common symptoms include:

  • Persistent fatigue

  • Emotional disturbances such as depression or anxiety

  • Difficulty concentrating or remembering things

  • Muscle tremors or spasms (myoclonus)

  • Poor coordination and trouble walking

  • Slurred or difficult speech

  • Headaches and personality changes

  • Social withdrawal

  • Delusions or psychotic episodes

  • Altered consciousness or disorientation

These symptoms can vary in severity and presentation, making diagnosis particularly challenging.

Underlying Causes

While the exact cause of Hashimoto's encephalopathy is not fully known, the condition is believed to stem from autoimmune processes. Similar to Hashimoto's thyroiditis, where the immune system attacks the thyroid gland, HE is thought to result from immune-mediated attacks on the brain.

What complicates the understanding of HE is the unclear relationship between brain dysfunction and thyroid hormone levels. In some individuals with HE, thyroid hormone levels remain within normal limits, while others may show signs of underactive or overactive thyroid function.

How HE Is Diagnosed

There is no definitive single test to diagnose Hashimoto's encephalopathy. Because its symptoms often resemble those of other neurological disorders, HE is frequently misdiagnosed as Alzheimer's disease, stroke, or Creutzfeldt-Jakob disease.

To arrive at a diagnosis, healthcare providers typically:

  • Rule out other conditions: Tests are conducted to eliminate possible causes such as infections, metabolic imbalances, or other types of encephalopathy.

  • Measure thyroid-related antibodies: The presence of elevated thyroid peroxidase (TPO) antibodies or antithyroglobulin (TG) antibodies suggests an autoimmune origin.

  • Evaluate thyroid hormone levels: Though not always abnormal, thyroid hormone tests help assess overall thyroid function.

  • Conduct imaging and brainwave tests:

    • MRI scans may show brain changes, although many individuals with HE have normal results.

    • EEGs (electroencephalograms) often reveal abnormalities, with the majority of people with HE displaying irregular brainwave activity.

  • Perform a lumbar puncture: High protein levels in cerebrospinal fluid, without signs of infection, can support the diagnosis.

A diagnosis of HE typically requires both the presence of thyroid antibodies and the exclusion of other potential causes.

Treatment Approaches

The cornerstone of HE treatment is corticosteroid therapy. Most patients respond favorably to oral steroids such as prednisone or IV administration of drugs like methylprednisolone. Rapid and substantial improvement in symptoms is a key characteristic of the condition.

For individuals who do not respond to steroids or who cannot tolerate them, alternative treatments may include:

  • Immunosuppressive medications such as cyclophosphamide or mycophenolate mofetil

  • Intravenous immunoglobulin (IVIG) to help modulate the immune response

  • Plasma exchange (plasmapheresis) to remove harmful antibodies from the bloodstream

Treatment duration varies depending on symptom severity and patient response, but some individuals may eventually be able to reduce or discontinue therapy under medical supervision.

Prognosis and Long-Term Outlook

While Hashimoto's encephalopathy is not considered curable, it is typically manageable with prompt and consistent treatment. Many individuals achieve remission and return to their regular activities. Relapse is possible but occurs in a relatively small percentage of patients. For those who do experience a relapse, it often involves re-emerging symptoms that respond well to reintroduction of treatment.

The overall prognosis for HE is favorable, particularly when recognized and treated early. Awareness among healthcare professionals and patients is essential to reducing the risk of misdiagnosis and delayed treatment.

Conclusion

Hashimoto's encephalopathy is a complex, immune-related brain disorder that often goes unrecognized due to its diverse and sometimes subtle symptoms. While the exact cause remains unclear, its association with thyroid antibodies points to an autoimmune mechanism. Despite its rarity, the condition is highly treatable—especially when diagnosed early.

If you or someone you know begins experiencing sudden neurological symptoms like confusion, memory loss, or unusual behavior, especially with a history of thyroid issues, it's crucial to bring up the possibility of Hashimoto's encephalopathy with a healthcare provider. Early diagnosis and treatment can make a significant difference in managing the condition and improving quality of life.