Hashimoto’s encephalopathy is a rare autoimmune condition in which the immune system attacks the brain, causing cognitive decline, seizures, psychiatric symptoms, or stroke-like episodes. Despite its name, it often has little to do with how well the thyroid is functioning. Up to 30% of people diagnosed with the condition have completely normal thyroid levels at the time of presentation, which is part of what makes it so confusing to identify.
Because the hallmark of this condition is its dramatic response to steroid treatment, many neurologists now prefer the name SREAT, which stands for steroid-responsive encephalopathy associated with autoimmune thyroiditis. That name better captures what’s actually happening: an immune process linked to thyroid antibodies, not a thyroid problem causing brain damage.
How It Presents
Hashimoto’s encephalopathy shows up in two broad patterns. About 75% of cases follow a chronic, progressive course. These patients experience a slow decline in thinking and memory, depression, tremors, and episodes that mimic strokes (occurring in over 65% of chronic cases). The stroke-like episodes are temporary, resolving on their own, but they can be frightening and are frequently misdiagnosed as actual strokes or transient ischemic attacks.
The remaining 25% of cases present acutely, with a rapid onset of confusion, fever, and seizures. Seizures occur in over 95% of acute presentations. Psychosis is common in both forms, with visual hallucinations reported in over 90% of cases. People have described seeing animals or figures that aren’t there, and some develop paranoid delusions or tactile hallucinations. An enlarged thyroid gland and blurred vision are also typical findings on physical examination.
Other neurological signs include exaggerated reflexes (found in roughly 85% of patients), involuntary muscle jerks called myoclonus, tremors, and difficulty with coordination and balance. The combination of cognitive problems, psychiatric symptoms, and neurological deficits can look remarkably like Creutzfeldt-Jakob disease, viral encephalitis, or even a brain tumor, which is why diagnosis often takes time.
What Causes It
The exact mechanism is still not fully understood, but Hashimoto’s encephalopathy is classified as an autoimmune condition. The immune system produces antibodies against thyroid proteins, and these antibodies appear to trigger inflammation in the brain. One specific antibody that researchers have identified targets a protein called alpha-enolase, which is found in brain tissue. When antibodies attack this protein, they can cause inflammation in specific brain structures, including the basal ganglia (deep brain regions involved in movement and coordination).
What’s important to understand is that the brain symptoms are not caused by thyroid hormone levels being too high or too low. Most patients are either euthyroid (normal thyroid function) or have only mild hypothyroidism that wouldn’t explain the severity of their neurological problems. This distinguishes Hashimoto’s encephalopathy from conditions like myxedema coma, where severe hypothyroidism directly impairs brain function.
How It’s Diagnosed
There is no single test that confirms Hashimoto’s encephalopathy. Instead, diagnosis requires meeting several criteria simultaneously, and it is largely a diagnosis of exclusion, meaning other causes must be ruled out first.
The key requirements include:
- Encephalopathy with cognitive impairment plus at least one of the following: psychiatric symptoms, seizures, myoclonus, or focal neurological deficits
- Elevated thyroid antibodies in the blood, specifically anti-TPO (thyroid peroxidase) or anti-thyroglobulin antibodies
- Normal or only mildly impaired thyroid function that wouldn’t account for the brain symptoms
- No other explanation found through blood work, spinal fluid analysis, or brain imaging
- Significant improvement with steroid treatment
Anti-TPO antibodies are elevated in virtually 100% of diagnosed cases, while anti-thyroglobulin antibodies are elevated in about 48%. The antibody levels can vary widely. Some patients show anti-TPO levels around 300 units, while others have levels exceeding 1,000 units. Brain MRI results are often normal or show only nonspecific changes, and EEG recordings typically reveal generalized slowing rather than a distinctive pattern. These tests are more useful for ruling out other conditions than for confirming this one.
Treatment and Response
The first-line treatment is high-dose corticosteroids, and the response can be remarkably fast. Treatment typically begins with intravenous steroids for three to five days. Some patients show dramatic improvement after just the second dose. After the initial course, patients transition to oral steroids, which are gradually tapered over weeks to months. One documented approach involved discharging a patient on daily oral steroids, then reducing to every-other-day dosing after three months.
About 75% of patients treated with corticosteroids show marked improvement, and a review of 105 cases found that 93% achieved either complete or partial neurological recovery. For the small percentage of patients who don’t respond to steroids, other immune-suppressing treatments can help. Intravenous immunoglobulin (IVIG) and plasma exchange have both shown effectiveness in steroid-resistant cases, with IVIG in particular gaining traction as a well-tolerated alternative with fewer side effects than long-term steroid use.
Relapse and Long-Term Outlook
The overall prognosis for Hashimoto’s encephalopathy is considered favorable compared to many other forms of encephalopathy, but the condition can come back. About 16% of patients experience a relapse within the first year after treatment. Some people require long-term immune-suppressing medication to stay in remission. The chronic progressive form, with its gradual cognitive decline, can be more difficult to manage than the acute form, partly because it’s harder to recognize and patients may go longer before treatment begins.
The biggest obstacle to a good outcome is delayed diagnosis. Because the symptoms overlap with so many other neurological and psychiatric conditions, patients may undergo extensive testing or receive incorrect diagnoses before anyone checks thyroid antibody levels. In cases of unexplained encephalopathy where standard workups come back negative, testing for anti-TPO antibodies is a relatively simple blood draw that can point toward a treatable cause.