Hashimoto’s encephalopathy is an uncommon disorder associated with inflammation of the thyroid gland (thyroiditis). The encephalopathy is thought to be most characterized by confusion, altered consciousness, and often seizures, but has been suggested to cause a wide range of symptoms.
While the syndrome is considered to be very rare, some researchers believe it to be under-diagnosed. Even very aggressive screening, however, leads to an estimated prevalence of about 2 per 100,000 people. The average age is thought to be in the early 40s, with women being more commonly affected than men.
Controversy exists about the nature and even the existence of Hashimoto’s encephalopathy. At the very least, it is very unclear whether the thyroiditis is the cause of the neurological symptoms, or if a shared autoimmune disorder happens to impact both the thyroid gland and the brain, as most researchers now believe. For example, thyroid hormone levels can be completely normal while the patient is confused (encephalopathic).
Cause of Hashimoto’s Encephalopathy
The immune system is meant to attack invading organisms like viruses and bacteria. Sometimes, however, the immune system mistakes part of the body, including part of the brain, as an invader, resulting in inflammation in brain tissue. Studies have shown inflammatory cells around the blood vessels in the brain. Antibodies against the thyroid are an essential component of the disease. The encephalopathy improves with anti-inflammatory treatments such as steroids.
Signs and Symptoms of Hashimoto’s Encephalopathy
Because the disease is rare and difficult to diagnose, it is difficult to even define the symptoms it causes. Generally, there may be a slowly progressive cognitive impairment with confusion and sometimes hallucinations or seizures. Alternatively, there may be several recurrent episodes of focal deficits and altered consciousness. About two–thirds of patients have seizures. The neurological examination may show myoclonus or increased reflexes.
Diagnosing Hashimoto’s Encephaloapthy
Because Hashimoto’s encephalopathy is treatable with steroids, it is important that it be recognized when present. Steroids can have side effects, and require a degree of certainty in the diagnosis before being given. While elevated anti-thyroid antibodies such as anti-thyroid peroxidase antibody or anti-thyroglobulin antibody correlate well with this encephalopathy, the antibodies are also high in up to 20 percent of healthy adults. Similarly, the degree of autoantibody elevation does not correlate with either the severity of symptoms or their improvement.
A lumbar puncture may be attempted in the diagnosis, as cerebrospinal fluid (CSF) abnormalities have been described in about 80 percent of patients with Hashimoto’s encephalopathy. The most common abnormality is an elevated protein concentration, though this finding is nonspecific and can be caused by a wide range of other neurological problems. More specific CSF findings such as oligoclonal bands or an increased IgG index have sometimes, but not always been reported.
Electroencephalography has been reported in at least 90 percent of patients with Hashimoto’s encephalopathy, though again, the findings are not specific to any particular disorder, but rather just show a general slowing of brain activity.
Neuroimaging studies such as magnetic resonance imaging (MRI) are usually normal. Sometimes there may be some signal hyperintensities in white matter, though such abnormalities are not uncommon even among patients without encephalopathy.
In short, high antithyroid antibodies are necessary for a diagnosis of Hashimoto’s encephalopathy, but not sufficient. Other available tests may be suggestive of the diagnosis, but are also not definitive, as the results are very nonspecific and can be caused by other disorders. The result is that while it is important to diagnose Hashimoto’s encephalopathy, doing so can also be challenging.
Treating Hashimoto’s Encephalopathy
The mainstay of treatment for Hashimoto’s is immune suppression with steroids. Other, more aggressive methods have also been used, but are less common. Even steroids have risks of side effects including mood swings, jitteriness, increased blood pressure, weight gain and more. Because the goal is to suppress the immune system, people who take steroids for a long period are also at an increased risk of infection.
By reducing inflammation in the body and increasing energy levels, steroids often make people feel better even if there is no major impact on the underlying illness. For this reason, it is difficult to use improvement on steroids as a sign that the disease was, in fact, Hashimoto’s encephalopathy. That said, over 90 percent of patients with Hashimoto’s improve with steroids, though some residual deficits may remain in about 25 percent of cases.
Brain L, Jellinek EH, Ball K. Hashimoto's disease and encephalopathy. Lancet 1966; 2:512.
Ferracci F, Bertiato G, Moretto G. Hashimoto's encephalopathy: epidemiologic data and pathogenetic considerations. J Neurol Sci 2004; 217:165.
Kothbauer-Margreiter I, Sturzenegger M, Komor J, et al. Encephalopathy associated with Hashimoto thyroiditis: diagnosis and treatment. J Neurol 1996; 243:585.