November 7, 2011
First described in 1966, Hashimoto's encephalopathy (HE) is still considered a controversial disorder, likely under-recognized, with diagnosis primarily based on exclusion. That is, if no other causes for the neurological symptoms are found and high titers of thyroid antibodies are present, a diagnosis of HE is made.
Several studies indicate that HE is associated with intrathecal production of thyroid antibodies although spinal fluid antibody titers do not correlate with disease severity. Diagnosis of HE is based on the presence of high titers of thyroid antibodies in the blood or thyroid antibodies in the spinal fluid along with inflammatory changes demonstrated on electroencephalograms (nonspecific slow background activity) and MRI (cerebral atrophy, focal cortical abnormality, diffuse subcortical abnormality and nonspecific subcortical focal white matter abnormality). Often, the C-Reactive Protein (CRP) and sed rates are elevated, and liver enzymes may be slightly elevated.
Subtypes and Symptoms
Occurring primarily in the fifth decade of life, HE may occur as a sudden vasculitic type or as a progressive subacute type associated with cognitive dysfunction, confusion and memory loss. HE primarily occurs in females (four times more often than in males) and is associated with Hashimoto's thyroiditis, Graves' disease, primary biliary cirrhosis, pernicious anemia, rheumatoid arthritis, glomerulonephritis, and myasthenia gravis.
One case report describes a previously healthy 62-year old woman who developed right arm tremor, enuresis (involuntary urination), slowness performing daily activities, difficulty walking and trouble dressing. Relatives reported transient episodes of disorientation and inappropriate irritability. Upon admission to a hospital, the patient was found to have trouble with speech (apraxia, dysphasia), attention deficity and amnesic episodes. The patient was also found to have hypothyroidism and was treated with thyroid replacement hormone. Symptoms persisted until she was later treated with prednisone. A good response to corticosteroids has traditionally been used to help confirm a diagnosis of HE.
Studies show that 25 percent of patients follow a stroke-like pattern of multiple recurrent episodes with variable cognitive dysfunction and consciousness impairment. About 75 percent of patients present with a diffuse progressive pattern of slow cognitive decline with dementia, confusion and hallucinations. These two subtypes may overlap over the course of the disease. Two-thirds of patients may have focal or generalized tonic-clonic seizures and 12 pecent may present with status epilepticus. Myoclonus or tremor is seen in 38 percent of patients and hyper reflexes may occur in up to 85 percent of patients.
Thyroid Status Association
Thyroid status in HE is variable. The results of two recent studies show that 23-35 percent of patients have subclinical hypothyroidism; 17-20 percent have hypothyroidism; 7 percent have hyperthyroidism and 18 to 45 percent of patients with HE were euthyroid at the time of diagnosis.
Most patients respond favorably to corticosteroids or a combination of corticosteroids and levothyroxine; occasionally, patients respond to levothyroxine alone.
Carlos Canello-Aybar, Hashimotos encephalopathy presenting with neurocognitive symptoms: a case report, Journal of Medical Case Reports, October 2010.