What Is Hashimoto's Encephalopathy?

Hashimoto's encephalopathy (HE) is a rare disease that involves impaired brain function (encephalopathy). The condition is named for its possible association with Hashimoto's thyroiditis, a common autoimmune thyroid disease, but the exact cause is not fully understood. HE contributes to neurological issues such as seizures, confusion, or dementia. It's usually reversible with treatment.

Hashimoto's encephalopathy is considered rare, affecting just two people out of every 100,000. However, it's likely that many more cases 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 40 to 55 years old. Women are diagnosed with it about four times more often than men. HE can also affect children, but that's believed to be rare.

Hashimoto's Encephalopathy Symptoms

Hashimoto's encephalopathy affects how your brain functions, causing cognitive decline and altered consciousness. It usually progresses in one of three ways:

• Relapsing and remitting: Episodes of acute symptoms come and go, often involving seizures and stroke-like attacks.
• Progressive: Cognitive decline gradually progresses into dementia, hallucinations, confusion, sleep-wake cycle impairment, or even a coma.
• Self-limiting: After a symptomatic period, the disease resolves on its own without treatment.

Symptoms common to the different types include:

• Depression, which may be the first symptom of the progressive form
• Fatigue
• Anxiousness
• Over-responsive reflexes
• Poor appetite
• Confusion
• Cerebral ischemia (lack of blood flow to areas of the brain)
• Altered consciousness
• Tremors
• Disorientation
• 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
• Headaches
• Lack of concentration and inattentiveness
• Emotional instability
• Withdrawal from social activities
• Personality changes

A 2016 review looked at how common various symptoms were among 251 people with HE.

Causes

It's unknown what exactly causes Hashimoto's encephalopathy, but scientists think that like Hashimoto's thyroiditis, HE is an autoimmune condition, meaning that the immune system mistakenly targets your body's own tissues as if they were a virus or bacteria. In the case of HE, the target is the brain.

In Hashimoto's thyroiditis, the immune system attacks the thyroid gland, causing hormonal problems. It's still unclear what the relationship is between these conditions.

Diagnosis

Currently, healthcare providers don't have a definitive test for Hashimoto's encephalopathy. Because its symptoms primarily affect your brain, HE is easy to misdiagnose or overlook. People are sometimes misdiagnosed with Creutzfeldt-Jakob disease, dementia, Alzheimer's disease, or stroke.

Diagnosis consists of first ruling out other known causes of encephalopathy, then checking for the presence of specific antibodies (the immune system's "attack" cells) and thyroid dysfunction.

Causes of Encephalopathy

The term "encephalopathy" isn't well-defined by medical science and instead serves as a broad term for diseases that alter the function or structure of the brain. Many diseases do this, including some that are chronic and others that are acute (short-term) and reversible.

Chronic encephalopathies usually result from permanent changes to the brain. They include:

• Traumatic brain injury
• Heavy metal exposure
• HIV-related changes
• Korsakoff encephalopathy
• Spongiform encephalopathies such as Creutzfeldt-Jakob

Acute encephalopathies include temporary changes in function due to:

• Toxins (e.g., medications, recreational drugs, or hazardous chemical exposure)
• Metabolic disturbances
• Combinations of the above causes, including kidney or liver failure, electrolyte imbalance, fever, infections, and nutrient deficiencies

Blood tests may be done to check for any of these possible causes, depending on what your healthcare provider believes are the most likely problems.

Antithyroid Antibodies

Testing for two antibodies that attack the thyroid gland—called thyroid peroxidase (TPO) antibodies and antithyroglobulin (TG) antibodies—is crucial since these are the key to a diagnosis of HE. In the aforementioned 2016 review, all 251 participants 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 person to person. According to a paper published in 2010:

• Between 23% and 35% of people with Hashimoto's encephalopathy have subclinical hypothyroidism (low hormone levels that don't meet the threshold for thyroid disease)
• Between 17% and 20% have primary hypothyroidism (underactive thyroid disease)
• About 7% have hyperthyroidism (overactive thyroid disease)

The 2016 review also found that most of the patients had normal levels of thyroid-stimulating hormone and only 32% had been previously diagnosed with thyroid disease.

Ruling Out Other Causes

A major part of diagnosing HE is running tests for other potential reasons behind your symptoms and ruling them out.

• A lumbar puncture, also known as a spinal tap, looks for high concentrations of protein in your cerebrospinal fluid, which is present in about 75% of HE cases. The fluid can also be cultured to find any bacteria, viruses, or other pathogens that could be causing your symptoms.
• Electroencephalography (EEG) is a non-invasive test that uses electrodes to measure your brainwaves. Abnormalities are found in between 90% and 98% of people with Hashimoto's encephalopathy.
• Magnetic resonance imaging (MRI), which produces detailed images of the brain. MRIs are usually, but not always, normal in HE.

Treatment

The primary treatment for Hashimoto's encephalopathy is oral corticosteroid drugs, usually prednisone, or intravenous (IV) Medrol (methylprednisolone). Most people respond quickly and well to drug treatment, with their symptoms improving or even resolving within a few months.

The 2016 review found that 91% of participants responded completely or by at least 50% to steroid treatment. Response to steroid treatment is considered part of what defines HE.

For people who can't take corticosteroids or whose symptoms didn't respond to them, other options are:

• Immunosuppressive medication like Cytoxan (cyclophosphamide), CellCept (mycophenolate mofetil), or Rituxan (rituximab)
• Intravenous immunoglobulin (IVIG), in which antibodies from healthy donors are delivered into the veins, which helps remove and/or inhibit the action of harmful antibodies
• Plasma exchange, in which your plasma (the fluid in your blood) is extracted and replaced with healthy plasma in order to remove harmful antibodies

Prognosis

Like most autoimmune disorders, Hashimoto's encephalopathy is not considered curable, but rather treatable. 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.

There is a risk of future relapse, but in the 2016 review, only 16% percent of patients had one or more relapses, and many of those people previously had severe HE that involved being in a coma.

Frequently Asked Questions

Which type of healthcare providers treats Hashimoto encephalopathy?

Neurologists are often the best-equipped specialists to diagnose and oversee treatment for Hashimoto encephalopathy. Other healthcare providers who may be involved in diagnosis and management of this autoimmune condition include rheumatologists, psychiatrists, psychologists, and immunologists.

Is Hashimoto encephalopathy a form of dementia?

Dementia is a symptom of Hashimoto encephalopathy (HE). HE may cause rapidly progressive dementia or dementia of unknown origin, but the cognitive changes may be reversible with proper treatment.

Summary

Hashimoto's encephalopathy causes symptoms like seizures, confusion, and memory problems. Its cause is unknown, but it's thought to be an autoimmune condition possibly related to Hashimoto's thyroiditis.

Diagnosis is a challenge and involves ruling out other possible causes, checking for specific antibodies, and monitoring thyroid function. Fortunately, most people respond well to treatment with steroids or other therapies, even if they aren't diagnosed for several years. 

If you or someone close to you develops acute neurocognitive symptoms that your healthcare provider can't explain, be sure to mention any personal or family history of Hashimoto's disease or other thyroid conditions so your practitioner can look into Hashimoto's encephalopathy as a possible cause of your symptoms.