Medicare is extending coverage of PET scans to include patients who meet the criteria for both frontotemporal dementia and Alzheimer's disease but for whom the diagnosis remains unclear.
The Centers for Medicare and Medicaid Services concluded in September that 18fluorodeoxyglucose PET (FDG-PET) imaging can be useful in patients with a documented cognitive decline of at least 6 months and a recently established diagnosis of dementia.
To be eligible for the new coverage, these patients must meet criteria for both frontotemporal dementia (FTD) and Alzheimer's disease (AD), but have an unclear diagnosis even after extensive clinical evaluation and alternative imaging (MRI and CT).
The specific conditions required to receive PET scan coverage to distinguish FTD and AD include:
▸ The onset, clinical presentation, or course of impairment is atypical for AD, and FTD is suspected as an alternative neurodegenerative cause.
▸ The patient has had a comprehensive clinical evaluation–as defined by the American Academy of Neurology–encompassing a medical history from both the patient and a well-acquainted informant, a physical and mental status examination aided by cognitive scales or neuropsychological testing, laboratory tests, and structural imaging.
▸ The patient has been evaluated by a physician experienced in the diagnosis and assessment of dementia.
▸ The evaluation did not identify a likely, specific neurodegenerative disease that is causing the clinical symptoms.
It's estimated that 12%-16% of patients with degenerative dementia may have FTD, which is often misdiagnosed as AD.
FTD is characterized by the formation of microvacuoles, gliosis with or without inclusion bodies, and swollen neurons.
FDG-PET imaging can be particularly useful in distinguishing frontotemporal dementia from Alzheimer's disease.
FDG-PET imaging assesses brain activity, with regions of atrophy appearing inactive.
FTD leads to frontotemporally predominant atrophy, while AD pathology is typically more severe in posterior temporoparietal regions–patterns that are distinguishable in a PET scan.
“This is important because the treatments for Alzheimer's disease do not help patients with frontotemporal dementia,” Gary W. Small, M.D., the director of the Center on Aging at the University of California, Los Angeles, said at a recent symposium on imaging sponsored by the Institute of Molecular Technologies.
Alzheimer's symptoms of memory and cognitive function impairment appear gradually.
Signs of frontotemporal dementia tend to appear as deficits in judgment and conduct, appearing early in disease development.
“There tends to be sort of a loosening of personality,” Dr. Small said.
CMS also concluded that although there are not adequate data to support the use of PET imaging for the diagnosis of patients with mild cognitive impairment or early dementia, the technique shows promise.