Is a Normal Brain MRI Common in Hashimoto's Encephalopathy?

Yes, a normal or non-specific brain MRI is frequently reported in Hashimoto’s Encephalopathy (also known as SREAT, or Steroid-Responsive Encephalopathy Associated with Autoimmune Thyroiditis) and does not rule out the diagnosis ^[1][2]. It is possible for patients to experience severe neurological symptoms while their MRI scans come back looking normal or showing only mild, non-specific changes ^[3].

Why Is the MRI Often Normal?

An MRI (Magnetic Resonance Imaging) is a detailed picture of the brain’s physical structure. While it can identify structural issues, conventional MRI may not detect the functional disturbances occurring in SREAT, and the exact reasons for this are not fully understood.

When researchers look at MRI results in SREAT patients, the estimates vary depending on the study size and criteria used. One review noted that specific, focal abnormalities on an MRI that can be tied to SREAT are found in fewer than 30% of cases ^[2]. Another small study of 13 patients found that nearly 85% of them had normal MRIs ^[3]. These percentages are not universal, but they highlight that normal scans are common. When changes are present, they are most often non-specific white matter hyperintensities—small bright spots that can be caused by many different things, such as aging or migraines, and do not specifically point to SREAT ^[2][4].

How is SREAT Evaluated if the MRI is Normal?

Because an MRI cannot definitively diagnose or rule out SREAT, doctors treat it as a “diagnosis of exclusion.” This means they must carefully rule out other causes of brain dysfunction—such as infections, metabolic imbalances, medication side effects, other autoimmune diseases, and structural issues—while gathering supportive clues ^[5][6]. If clinically appropriate, specialists may consider:

• Electroencephalogram (EEG): An EEG measures the brain’s electrical activity. In one large review, an EEG was abnormal in roughly 82% of reported SREAT cases ^[7]. The most common finding is diffuse slowing, meaning the brain’s overall electrical rhythm is slower than normal ^[7]. While this supports the presence of diffuse brain dysfunction, it is non-specific and can be caused by medications, infections, or other illnesses. An EEG can also help detect hidden seizures, though prolonged monitoring is sometimes needed if a routine EEG misses them ^[8][7].
• Lumbar Puncture (Spinal Tap): Analyzing the cerebrospinal fluid (CSF) can look for signs of inflammation. Some patients with SREAT have elevated protein levels or mildly elevated white blood cells (pleocytosis) in their CSF ^[3][9]. However, CSF can also be completely normal, these findings are non-specific, and the procedure carries some risks.
• Clinical History and Blood Tests: Doctors look closely at the rapid onset of symptoms like confusion, cognitive decline, seizures, or coordination issues. They will also test for antithyroid antibodies, such as anti-TPO ^[5][7]. While high antibody levels are supportive, they are common in people with ordinary thyroid disease, their direct role in causing brain symptoms is actively debated, and they do not prove a SREAT diagnosis on their own ^[7][10].

What You Should Know

If your brain MRI is normal, it is understandable to worry that your care team will not believe your symptoms. A normal MRI is helpful because it makes some large structural abnormalities, like large tumors or major strokes, less likely. However, it does not rule out all physical conditions (such as small strokes or early disease) and does not mean your symptoms are imagined.

Because SREAT involves a complex, uncertain diagnostic process, it is important to follow your doctor’s evaluation closely. Seek urgent or emergency medical care if you experience a first or prolonged seizure, rapidly worsening confusion, new weakness, speech trouble, severe headache with a fever, or an inability to stay awake, rather than waiting for outpatient testing.