Applying Imaging to the Diagnosis of Memory Disorders: Positron Emission Tomography (PET) Scanning

Concetta Forchetti, MD, and Jennifer Clauson

The diagnosis of a memory disorder such as Alzheimer’s disease is usually prompted by a subjective complaint; for example, a patient (or a family member) reports difficulty remembering information or making decisions, or more frequent misplacement of objects. After age 65, all patients should undergo simple neuropsychological tests (e.g., the Mini-Cog test)¹ as part of their annual exam. However, subjective complaints sometimes signal the early stages of a memory disorder, even if the Mini-Cog test is normal. Patients might be referred for formal neuropsychological testing, which is considered the gold standard for diagnosing a memory disorder.

The Memory Disorder Center at the AMITA Health Neurosciences Institute has a group of board-certified and experienced adult neuropsychologists who can administer these tests. Neurologists also can start the process of ruling out other conditions, including stroke, which can cause cognitive decline. Magnetic resonance imaging (MRI) can detect anatomical signs of stroke, as well as identify brain atrophy that occurs secondary to dementia. Once other conditions have been ruled out, patients might undergo more specific diagnostic testing to detect beta amyloid, a protein fragment that aggregates in the brain to form plaques characteristic of Alzheimer’s disease and other memory disorders.

Positron Emission Tomography (PET) Scanning

For many years, the only way to definitively diagnose Alzheimer’s disease or other beta amyloid-related memory disorders was to detect beta amyloid protein and aggregates in the brain at autopsy. The advent of beta amyloid PET scanning has made it possible to non-invasively detect beta amyloid fragment in the brain earlier in disease progression.^2,3 An earlier diagnosis of a memory disorder such as Alzheimer’s disease can give patients time to make lifestyle changes and plan for the future, as well as give them access to new investigational medications under development. An earlier diagnosis can also provide important information to future generations about their own risk of developing memory disorders.

Conversely, beta amyloid PET scanning can also help to confirm a false positive diagnosis or correct a misdiagnosis of Alzheimer’s disease. One patient seen at the Memory Disorders Clinic at the AMITA Health Neurosciences Institute had been diagnosed with Alzheimer’s disease two years prior based on EEG and other tests. She was referred to the Memory Disorders Clinic for a second opinion and underwent a PET scan. Her results were negative for beta amyloid, and she subsequently underwent an MRI to further investigate the cause of her symptoms. A 24-hour EEG and MRI identified a focus of seizure in the hippocampus, the same area of the brain where beta amyloid accumulation affects memory and cognitive function in Alzheimer’s disease. The patient was treated for the seizures and is now doing well. As another example, depression in the elderly can be mistaken for early symptoms of Alzheimer’s disease. A patient was referred to the Memory Disorders Clinic because of a change in energy levels and excessive crying and was found to have a negative PET scan result, which ruled out Alzheimer’s disease. The patient was referred to a neuropsychiatrist who adjusted his medications and provided counseling support, and the patient is now doing well.

There is a less expensive and similarly sensitive test that can measure beta amyloid in the cerebrospinal fluid (CSF) — however, it requires a lumbar puncture and can cause a prolonged headache. PET scanning is much less invasive. Although a small amount of radioactive material (tracer) is injected to detect beta amyloid, the majority of the tracer is excreted from body four hours after injection (half-life of 110 minutes). Patients might experience a reaction at the injection site.

“By referring patients to be evaluated for the IDEAS demonstration study and clinical trials of beta amyloid PET scanning, physicians can not only provide valuable options to their current patients, but also potentially help thousands of people and change lives by adding to the evidence base that PET scanning can definitively diagnose — or rule out — Alzheimer’s disease and other amyloid-related memory disorders at an early stage.”

– Concetta Forchetti, MD, PhD

Beta amyloid PET scanning has been used primarily in research and clinical trials. Since its use in the clinic is currently limited by its high cost, the AMITA Health Neurosciences Institute has two ways a patient can undergo a beta amyloid PET scan for the diagnosis of a memory disorder. First, patients can be enrolled in the Medicare demonstration study called “Imaging Dementia – Evidence for Amyloid Scanning” (IDEAS),⁴ which is examining the cost-effectiveness of amyloid beta PET scanning by studying differences in healthcare utilization (such as the number of hospitalizations or emergency department visits) based on PET scan results. People who are 65 years of age and over and who have Medicare as a primary insurance can qualify to undergo a beta amyloid PET scan and Medicare will reimburse providers for the cost of the scan. Patients are responsible for any copays or deductibles. Patients can be referred to Concetta Forchetti, MD, PhD, or Ajay Sood, MD, PhD, who are IDEAS participating physicians, to schedule a PET scan (884.366.0623). As IDEAS participants, patients will have one follow-up visit at the Memory Disorders Clinic at the AMITA Health Neurosciences Institute, and then return to their referring physician’s care. The results of the PET scan and any other relevant information will be shared with the referring physician.

The Memory Disorders Clinic joined the IDEAS demonstration trial not only to make amyloid beta PET scanning available to its patients, but also to help prove the benefits of testing. To date, the AMITA Health Neurosciences Institute has performed the most PET scans under the IDEAS study in Illinois: 105 patients, with five to 10 patients added each week.

The second opportunity for patients to undergo a beta amyloid PET scan is to enroll in an ongoing clinical trial at the AMITA Health Neurosciences Institute, which is open to people who are healthy, age 65 or older and who might be at increased risk for Alzheimer’s disease. Referring physicians are invited to contact the Clinical Research Office at 847.593.8553 for more information about the clinical trial.