Transmissible spongiform encephalopathies (TSE) are difficult to positively diagnose. When a TSE is suspected, treatable forms of dementia (e.g., encephalitis, chronic meningitis) must first be ruled out. This may involve a spinal tap or computerized tomography (CAT scan) of the brain. After other forms of dementia have been ruled out, a probable diagnosis of a TSE can be made by a physician’s evaluation of the patient’s medical history, the presentation of signs and symptoms, magnetic resonance imaging (MRI) of the brain and an electroencephalogram (EEG). Many types of TSEs cause unique abnormalities on EEG or brain MRI.

TSE can be positively diagnosed using a brain biopsy. This is an invasive and risky procedure that removes a small amount of brain tissue for laboratory examination. However, the tissue may be taken from a part of the brain that is not affected by the disease, resulting in a false negative result. TSE can be positively diagnosed with the greatest degree of reliability through a microscopic examination of brain tissue during an autopsy. However, this is only possible after death.

Research on new diagnostic tests for TSE is ongoing.