Diagnosis

The process of diagnosing prion diseases starts with a clinical interview and a neurological examination. If the signs and symptoms observed during the visit are compatible with the disease, additional tests are carried out to support the diagnosis and rule out other diseases:

• MRI. In 85% of cases, MRI can show changes in the brain such as an increased signal in certain sequences that make different parts of the brain (basal ganglia and cerebral cortex) ‘light up’ in a characteristic way.
• Cerebrospinal fluid analysis. A sample is obtained by making a prick in the lower back. Because this fluid is in contact with the brain, analysing it allows changes in the brain to be identified. The detection of 14-3-3 proteins as a marker of neuronal damage and the presence of pathological prion protein in this fluid are extremely helpful when diagnosing these diseases.  
• Genetic testing: as 10-15% of cases are genetic, genetic testing is recommended for patients with prion diseases.  
• Electroencephalogram: this consists of placing several electrodes distributed on the head to painlessly record brain activity. They allow the medical team to rule out other diseases such as epilepsy, and provide data to support the prion disease diagnosis.

As is the case with all neurodegenerative diseases, the definitive diagnosis of prion diseases is by post-mortem examination of the brain tissue. However, current diagnostic tests allow a very accurate diagnosis to be made while the patient is alive.