An Overview of Hashimoto's Encephalopathy

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Hashimoto's encephalopathy (HE) is a rare disease associated with Hashimoto's thyroiditis, an autoimmune thyroid disease that's the most common cause of an underactive thyroid (hypothyroidism) in the United States. It affects the brain, contributing to issues such as seizures, confusion, or dementia. Because most patients have no evidence of Hashimoto's disease, some experts are suggesting that the condition should be renamed to steroid-responsive encephalopathy associated with autoimmune thyroiditis (SREAT).

Prevalence

Hashimoto's encephalopathy is considered rare, with an estimated prevalence of 2.1 people in 100,000. However, it's likely that there are many more people who are undiagnosed or misdiagnosed since the condition isn't well-understood or highly recognized.

The average age of onset of symptoms of Hashimoto's encephalopathy is around 41 to 44 years old. Like other autoimmune conditions, women are more likely to have HE; about four women are diagnosed with HE for every one man. HE can also affect children, but there aren't many cases reported in the literature.

Symptoms

Hashimoto's encephalopathy affects how your brain functions and it usually progresses in one of two ways:

  • Acute, stroke-like attacks and/or seizures
  • A progressive cognitive decline into dementia, hallucinations, confusion, sleepiness, or even a coma

The two patterns can overlap too, and both commonly have other symptoms such as:

  • Disorientation
  • Tremors
  • Concentration and memory problems
  • Psychosis and delusional behavior
  • Spasms and jerks in the muscles known as myoclonus
  • Lack of muscle coordination, which can cause difficulty walking
  • Speech problems
  • Depression
  • Irritability
  • Headaches
  • Paralysis
  • Behavioral changes
  • Personality changes
  • Anxiety

A 2016 review of 251 cases of Hashimoto's encephalopathy also found the incidence of various symptoms among the patients.

  • Seizures (47 percent)
  • Confusion (46 percent)
  • Impaired memory (43 percent)
  • Speech problems (37% percent
  • Difficulty walking (27 percent)
  • Delusions in which the patient believes he or she is being persecuted (25 percent)
  • Myoclonus (22 percent)
  • Headaches (16 percent)
  • Coma (15 percent)
  • Depression (12 percent)

Causes

It's unknown what exactly causes Hashimoto's encephalopathy, but scientists think that like Hashimoto's disease, Hashimoto's encephalopathy is autoimmune, meaning that it's caused by an aggressive but mistaken immune system targeting your body's own organs, glands, and tissues. In the case of Hashimoto's encephalopathy, the target is the brain. It's still unclear what the relationship is between HE and Hashimoto's disease, however.

Diagnosis

Currently, there isn't a definitive test for Hashimoto's encephalopathy. Because its symptoms primarily affect your brain, HE is easy to misdiagnose or overlook. Sometimes patients are misdiagnosed as having Creutzfeldt-Jakob disease, dementia, Alzheimer's disease, or as having had a stroke.

Diagnosis consists of ruling out other known causes of encephalopathy, as well as blood tests to check for the presence of specific antibodies.

Blood Tests

Your doctor will likely start by having your blood drawn to do tests that look for certain antibodies, as well as for other potential causes of your symptoms.

Antithyroid Antibodies

Testing the antithyroid antibodies called thyroid peroxidase (TPO) antibodies and antithyroglobulin (TG) antibodies is crucial since these are the key to a diagnosis. The aforementioned 2016 review found that all of 251 the patients had increased levels of one or both of these antibodies.

Thyroid Hormone Levels

Thyroid hormone levels are usually tested as well, but these vary from patient to patient. Studies have estimated that 23 percent to 35 percent of people with Hashimoto's encephalopathy have subclinical hypothyroidism, 17 percent to 20 percent have primary hypothyroidism, and 7 percent have an overactive thyroid (hyperthyroidism).

The same 2016 review found that most of the patients had normal TSH levels. Only 32 percent had been diagnosed with thyroid disease.

Other Blood Tests

Your doctor will also likely check your blood for other problems in your body that may be causing your symptoms, such as an infection, tumor, metabolic dysfunction, or a toxic agent. This could include testing levels such as your electrolytes, creatinine, glucose, calcium, and doing a complete blood count (CBC).

Ruling Out Other Causes

A major part of diagnosing HE is checking for other potential reasons behind your symptoms and ruling them out. Tests that may be performed include:

  • A lumbar puncture, also known as a spinal tap, to look at your cerebrospinal fluid for an elevated concentration of protein (which occurs in about 75 percent of HE patients) and to do a culture that looks for the presence of bacteria, viruses, or other organisms that could be causing your symptoms.
  • Electroencephalography (EEG), a non-invasive test that uses electrodes to measure your brainwaves. Abnormalities are found in 90 percent to 98 percent of people with Hashimoto's encephalopathy.
  • Magnetic resonance imaging (MRI), which is usually, but not always, normal in HE.

In order to be diagnosed with HE, you must have elevated anti-TPO antibodies and/or anti-TG antibodies present. Other potential causes of your symptoms must have been ruled out as well.

Treatment

The primary treatment for Hashimoto's encephalopathy is oral corticosteroid drugs, usually prednisone or intravenous (IV) Medrol (methylprednisolone), though prednisone was just as effective as IV Medrol in the 2016 review.

Most patients respond quickly and well to drug treatment, with their symptoms improving or even resolving within a few months. The 2016 review found that 91 percent of patients responded completely or by at least 50 percent to steroid treatment. Along with elevated antithyroid antibodies, responding to steroid treatment is what defines HE.

For people who can't take corticosteroids or whose symptoms didn't respond to them, another option is immunosuppressive medication like Azasan or Imuran (azathioprine) or cyclophosphamide. Some patients have also been reported to respond well to immunoglobulin and plasma exchange.

Prognosis

Like most autoimmune disorders, Hashimoto's encephalopathy is not considered curable, but rather treatable and the prognosis is generally good. After initial treatment, the disorder often lapses into remission. Some patients are able to discontinue drug therapy for a number of years, though there is a risk of future relapse.

In the 2016 review, only 16 percent of patients had one or more relapses, and many of those had been in a coma the first time.

A Word From Verywell

Hashimoto's encephalopathy can create a bit of a diagnostic challenge. Fortunately, most people respond well to treatment, even if they aren't diagnosed for several years. If you or your child suffer acute neurocognitive symptoms that your doctor can't explain, be sure to mention any personal or family history of Hashimoto's disease or other thyroid conditions so your doctor can look into Hashimoto's encephalopathy as a possible cause of your symptoms.

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