Encephalopathy is a term for any diffuse disease of the brain that pathologically alters brain structure or function. Hashimoto’s encephalopathy (HE) is so termed due to historical circumstances because the condition was first described in a patient with Hashimoto's thyroiditis who displayed cognitive and neurological abnormalities.
Most scientists believe the name “Hashimoto’s Encephalopathy” is ill-advised since the disease is not causally related to Hashimoto’s thyroiditis (HT), despite the fact that HT is usually present in patients with HE. It is this correlation that originally led to the creation of the term Hashimoto’s Encephalopathy. Until scientists find common ground and settle on an accepted name, we will use HE as a shorthand way of referring to Hashimoto’s Encephalopathy. HE is recognized as a rare disease by the U.S. National Institutes of Health’s Office of Rare Diseases Research, which refers to it as “Hashimoto’s encephalitis,” however it is recently being discovered that like other autoimmune encephalitis, it may not be as rare as once believed. Due to the lack of knowledge to many in the medical professions, AE/HE are not identified and treated as commonly as they should.
It is not yet known what causes HE. Unlike many other autoimmune encephalitis, there is no known antibody (sero negative) or virus that causes the autoimmunity against the brain and nervous system. More research is needed. The high thyroid antibodies such as the thyroid peroxidase (TPO) or thyroglobulin (TgAb) are only a marker used to help with the diagnosis of HE and as of yet are not proven to have any role in causing damage to the brain and nervous system.
Research studies and case summaries are generally based on small patient populations, use different criteria for inclusion and may not include comprehensive demographic or health history details. Tests and findings across case reports often vary widely.
A Study by Mayo Clinic
Who Gets HE?
HE strikes people, adults and children alike from all walks of life. HE diagnosis does occur more frequently in women than men in a ratio that appears to be at least 2:1. The most common ages of patients being in their 40's and 50's. There is suspicion, among both patients and physicians, that HE is under-diagnosed, and perhaps not consistently diagnosed across populations. This makes it difficult to explain what the "typical" HE patient looks like.
How Common is Autoimmune Encephalitis?
A Study by Mayo Clinic
To identify cases of encephalitis, the study used data from the Rochester Epidemiology Project, a medical records database of all medical providers in Olmsted County, Minnesota. The researchers found about 14 per 100,000 people had autoimmune encephalitis in their lifetime, compared to 12 per 100,000 who had infectious encephalitis. One study limitation is that the diagnostic criteria for autoimmune and infectious causes of encephalitis differed, which could affect the comparison.“Previously, we did not know how common autoimmune encephalitis was, as no prior studies evaluated this,” Dr. Flanagan says. “This study allows us to estimate that approximately 1 million people worldwide had autoimmune encephalitis in their lifetime. We also estimate that, currently, about 90,000 people around the world develop autoimmune encephalitis each year.”
In this study, the researchers used 2016 diagnostic criteria for autoimmune encephalitis. Using the Mayo Clinic Neuroimmunology Laboratory, which performs comprehensive neural autoantibody testing on blood and spinal fluid, the researchers were able to identify neural antibody markers that indicate a likely autoimmune cause.
“Our study showed that clinicians are now detecting more cases of autoimmune encephalitis than they were in the past because of the discovery of these new neural autoantibody markers. These advances in diagnostic testing are good news for patients, as they have allowed doctors to diagnose and treat autoimmune encephalitis more effectively.” Dr. Flanagan says.
How is Hashimoto's Encephalopathy Related To Hashimoto's Thyroiditis?
It is important to note that while elevated antithyroid antibodies are present in both Hashimoto's thyroiditis and Hashimoto's encephalopathy, and while both conditions have "overlapping" symptoms such as fatigue and cognitive difficulties, they are nevertheless ENTIRELY seperate conditions with their own distinct causes, treatments and prognosis.
Are There Different Types of HE?
HE symptoms are generally reported to follow one of two patterns:
Relapse remitting- stroke-like episodes, with transient focal neurological deficits. Symptoms vary in intensity and duration and can come and go quickly
Progressive- It may be more frequently characterized by dementia and psychiatric symptoms.
Many patients, however, display an overlap in symptoms between the two types.