How Is SREAT Differentiated From Dementia and CJD?

SREAT (Steroid-Responsive Encephalopathy Associated with Autoimmune Thyroiditis), also known as Hashimoto’s encephalopathy, is a condition that must be carefully differentiated from neurodegenerative dementias and other brain disorders. SREAT is considered a “diagnosis of exclusion” ^[1]. This means doctors must systematically rule out other causes—such as infections, toxins, vascular disease, or tumors—before attributing symptoms to SREAT ^[2].

Urgent Warning: Symptoms like rapidly worsening confusion, a first or prolonged seizure, fever with altered mental status, new weakness, or an inability to walk require immediate emergency medical evaluation ^[2]. Do not wait for an outpatient appointment or start any treatments without medical supervision.

Symptom Timing and Features

While typical neurodegenerative dementias like Alzheimer’s disease usually progress gradually over years, SREAT often presents as an acute or subacute encephalopathy (a broad term for a disease that affects the brain’s function or structure, causing altered mental status) that develops over days to weeks ^[3]. However, some dementias can progress rapidly, and some cases of SREAT develop more slowly, so timing alone is not enough to make a diagnosis ^[4].

SREAT is often accompanied by physical neurological symptoms, such as:

• New, unexplained seizures ^[3].
• Aphasia (difficulty speaking or understanding language) ^[4].
• Severe gait disturbances (unsteadiness when walking) ^[3].
• Stroke-like episodes or prominent psychiatric symptoms ^[4].

These features help clinicians distinguish SREAT from typical early dementia, though none of these symptoms confirm SREAT on their own ^[4].

The Graus 2016 Criteria for Autoimmune Encephalitis

Because there is no single test for SREAT, neurologists often use the Graus 2016 consensus criteria to evaluate patients for possible autoimmune encephalitis (brain inflammation caused by the immune system) ^[5][4]. Meeting these criteria does not specifically confirm SREAT, but it provides a framework for evaluation. The criteria require:

1. A rapid onset (less than three months) of memory deficits, altered mental status, or psychiatric symptoms ^[5].
2. At least one of the following: a new focal finding in the central nervous system, an unexplained seizure, CSF pleocytosis (an increased white blood cell count in the spinal fluid), or MRI features suggestive of encephalitis ^[5].
3. The reasonable exclusion of alternative causes ^[5].

While an abnormal EEG (electroencephalogram, a test that measures brain waves) often shows diffuse slowing in SREAT and can be a helpful clue, it is not one of the specific four alternative features required by the Graus criteria for possible autoimmune encephalitis ^[5].

Why Thyroid Antibodies Are Not Enough

Elevated thyroid antibodies (such as anti-TPO) are a defining feature of SREAT, but they do not prove that a patient has the condition ^[4][6]. These antibodies are relatively common in the general population and can be found in people with normal thyroid function, primary psychiatric disorders, and unrelated dementias ^[6][4]. Furthermore, antibody levels do not reliably correlate with the severity of brain symptoms ^[7]. Therefore, doctors must find objective evidence of brain dysfunction or inflammation (like specific MRI or spinal fluid findings) rather than relying on blood tests alone ^[4].

Differentiating from Creutzfeldt-Jakob Disease (CJD)

SREAT can sometimes mimic Creutzfeldt-Jakob disease (CJD), a rare, rapidly progressive, and fatal neurodegenerative disease ^[8]. Doctors look for clues to differentiate them: seizures and spinal fluid inflammation are more frequently seen in SREAT ^[8], while myoclonus (sudden muscle jerks) and akinetic mutism (an inability to move or speak) point more toward CJD ^[8].

To help distinguish between the two, doctors may perform a lumbar puncture (spinal tap) to test the cerebrospinal fluid using an RT-QuIC test ^[9]. A positive RT-QuIC strongly supports a diagnosis of prion disease like CJD ^[9]. However, a negative test does not completely rule out CJD, nor does it directly confirm SREAT ^[9]. Test results must always be interpreted alongside MRI scans, EEGs, and physical examinations ^[9].

The Role of a Steroid Trial

SREAT is named for its response to corticosteroids, but a “steroid trial” is not a standardized diagnostic test ^[6]. There is no universally accepted dose, duration, or response threshold ^[6]. If an individualized trial is directed by a neurologist, it may support a working diagnosis of SREAT if the patient improves ^[3]. However, improvement is not specific to SREAT, as steroids can temporarily improve symptoms of other inflammatory conditions or tumors, and a lack of improvement does not reliably exclude SREAT ^[6][3].

Before and after treatment, doctors may use objective measures—such as a formal cognitive assessment, an EEG, or observation of daily function and seizures—to track changes ^[10][11]. Steroids should never be started without medical supervision, as they can worsen unrecognized infections, obscure malignancies, and cause severe side effects like sleep changes, high blood sugar, and mood alterations.