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loss) in characteristic distributions is another biomarker that identifies the predementia form of Alzheimer's disease. While causation is a hotly disputed topic, it suffices to say that the earliest pathologic process involves the entorhinal cortex (ERC) in the medial temporal lobe and results in a functional disconnection of the hippocampus. While atrophy of the medial temporal lobe evolves over time, neuronal dysfunction is ongoing in the network of neurons connected to the ERC. PET can be difficult to accurately assess for early pathology. STRIC is fortunate to have FDA-approved quantitative analysis software that compares patients' FDG- PET regional uptake with that of normal cohorts. This has been an invaluable tool in increasing confidence levels and sensitivity in the detection of early Alzheimer's disease and in differentiating from frontotemporal lobe dementias. The high sensitivity and specificity of FDG-PET compared with cognitive test- ing and clinical assessment has led the American Academy of Neurology to modify its algorithm in the evaluation of cognitive impairment to include earlier FDG-PET scanning. As with many new imaging modali- ties, it is possible to overstate the accuracy of differentiation between Alzheimer's disease and frontotemporal lobe dementias. There is some overlap between hypometabolism patterns. While the cholinesterase inhibitors used to treat Alzheimer's disease are of no value to patients with frontotem- poral lobe dementia, it would be most unfortunate to make a diagnostic error that would deny a patient a chance to maintain cognition and independence for any amount of time. The FDA has recently approved Amyvid, an isotope for amyloid PET imaging that uses radioactive fluorine attached to an agent that binds amyloid plaques in the brain. The amyloid plaque is one of the pathologic substrates of Alzheimer's disease. (Tau protein in neurofibrillary tangles is another.) A positive Amyvid scan indicates moderate to frequent amyloid neuritic plaques. Amyvid is commercially available but extremely expensive compared to FDG. The Centers for Medicare & Medicaid Services has not yet provided guidance or approval for reimbursement. How this agent will fit into our toolbox from both cost and efficacy perspectives is to be determined. Until the pathophysiol- ogy of the disease is better established, leading to effective treatment and prevention, I will continue to focus on the tools currently available to make an early and accurate diagnoses of the progressive neurodegenerative diseases. Barry J. Menick, M.D., is a fellowship- trained diagnostic neuroradiologist with a special interest in neurodegenerative disor- ders. He received his medical degree from the Duke University School of Medicine in 1981. Dr. Menick completed his radiology residency and a two-year neuroradiology fellowship at the Hospital of the University of Pennsylvania in Philadelphia. He has been a senior member of the American Society of Neuroradiology since 1991. For more information, please contact South Texas Radiology Imaging Centers at (210) 319-4021, visit www.stric.com or follow STRIC on Facebook. ■ MDNEWS.COM ■ MD NEWS San Antonio | 11