Efforts are underway to persuade the Health Care Financing Administration (HCFA) to expand Medicare coverage for positron emission tomography, popularly known as PET scanning. At present, the government only reimburses charges for PET scans in connection with the diagnosis of lung cancer.
Efforts are underway to persuade the Health Care Financing Administration (HCFA) to expand Medicare coverage for positron emission tomography, popularly known as PET scanning.
Last January, HCFA conducted a town meeting in Baltimore designed to let researchers and clinicians present the case for bringing their own specialties under the Medicare umbrella.
At present, the government only reimburses charges for PET scans in connection with the diagnosis of lung cancer. PET is used to differentiate benign from malignant solitary pulmonary nodules, to stage mediastinal and distant disease, and to monitor the effectiveness of therapy.
Because HCFA represents the largest third-party payer for medical care, approval by the government agency virtually ensures that other insurance plans and managed care organizations will at least review the use of PET for their own programs. Meanwhile, researchers are reporting that PET is enabling them to make significant strides in the early detection of Alzheimer's disease (AD) and the differentiation of types of dementia.
"PET is very helpful for early diagnosis and for predicting the prognosis," said meeting participant Gary W. Small, M.D., professor of psychiatry and biobehavioral sciences at the University of California, Los Angeles, and director of the UCLA Center on Aging. "The data are suggesting that you can see the abnormal pattern in brain activity years before the symptoms are apparent to clinicians.
"There are some very effective treatments that can be instituted with early diagnosis," he added, noting, "There are even some neurologists who aren't aware that there are early treatments available for Alzheimer's."
While no one is predicting a timetable for HCFA's possible adoption of broader reimbursement guidelines for PET, a spokesperson for the agency noted that the Baltimore meeting was the prototype for a new set of procedures aimed at improving the decision-making process.
Beginning this year, a 120-member Medicare Coverage Advisory Committee (MCAC) is replacing the old Technology Advisory Committee, which was disbanded in January 1998 after the General Accounting Office ruled it was not in compliance with the federal law governing advisory committees. The MCAC will be subdivided into specialty panels that will conduct further town meetings to review possible changes or expansions in coverage.
While the new system was not fully implemented in January, the PET meeting followed the format outlined in the Federal Register last December, following approval of the MCAC charter by the Health and Human Services Department in November.
Under the procedures outlined for the MCAC, once the meeting has been conducted, the panel responsible for a given area will make recommendations for a technology assessment that could lead to approval of a new protocol. A source close to HCFA said the PET meeting generated enough evidence-based data that the technology assessment may not be necessary, and that the agency's chief medical officer may feel comfortable making the decision to expand coverage without further study.
"We're getting our first glimpse of how the new Medicare Coverage Advisory Committee is going to work, with its reliance on clinical panels and evidence-based presentations," an HCFA official said. "When was the last time you heard of a payer our size holding a town meeting on a coverage issue? We think Medicare is taking an interesting step here, trying to make its coverage process more open, accessible and understandable."
PET is not new technology. It has been used in the lab since the early 1980s, Small noted. But a recent wave of new research is generating expanded interest in its clinical application. It differs from other imaging tools, such as MRI and CT scans, by visualizing metabolic processes rather than anatomical structures. CT and MRI show nonspecific atrophy or focal lesions but fail to provide a positive diagnosis of AD, according to Small.
These recent studies appear to be pointing the way to early diagnosis and treatment for AD, which until now has often been missed in clinical examinations. Small told the HCFA meeting that "two-thirds of the cases diagnosed as Alzheimer's disease are found by autopsy."
In an interview, Small said, "Alzheimer's disease is prevalent and costly, but it can be treated in its early stages. The current approach to diagnosis involves multiple costly assessments. Very often, the clinician won't be sure of the diagnosis. PET allows early positive differential diagnoses for Alzheimer's and other diseases-years before the disease appears clinically.
"The estimated costs of Alzheimer's in the United States approach $100 billion," he added. "That makes it the third most costly illness. Most mild cases go unrecognized. In one survey, only 15% of the number of cases expected [based on epidemiological projections] were actually documented in hospital records. Other studies have found that in 50% of cases, close family members don't recognize the patient's symptoms. Even when a family member recognizes the symptoms, at least 50% of the time the diagnosis is missed." The accuracy of clinical diagnosis, he added, is as low as 60%, even in experienced settings.
Researchers say they are isolating tools for early diagnosis and treatment. A fluorine isotope known as [18F]-labeled 2-deoxyglucose, or FDG, mimics the absorption of normal glucose in the brain and is widely used for neurological studies. Small and his UCLA team used PET and FDG to measure cerebral glucose metabolism in subjects at risk for AD and found that the inheritance of the gene apolipoprotein E type 4 allele (APO E4) appears to be associated with reduced cerebral parietal metabolism and increased left-right asymmetry in individuals at risk for AD.
In 1996, Eric M. Reiman, M.D., and his colleagues at the University of Arizona reported using PET to investigate regions of the brain in which the rate of glucose metabolism declines progressively in patients with probable AD. They found that "in late middle age, cognitively normal subjects who are homozygous for APO E4 have reduced glucose metabolism in the same regions of the brain as patients with probable Alzheimer's disease. These findings provide preclinical evidence that the presence of the APO E4 allele is a risk factor for Alzheimer's disease. PET may offer a relatively rapid way of testing future treatments to prevent Alzheimer's disease."
The impact of early diagnosis could be an increase in the use of cholinesterase inhibitors and other agents that delay the onset of the disease. Small's group looked at patients receiving donepezil (Aricept) treatment over a six-month period. At the end of the study, only 5% of the patients receiving donepezil were institutionalized for AD, compared with 10% of the patients not taking donepezil.
Another study by David Knopman, M.D., of the University of Minnesota department of psychiatry, and others found that patients receiving the cholinesterase inhibitor tacrine (Cognex) in large doses over a 30-week period were less likely to be placed in nursing homes. Nursing home placement, the researchers wrote, "is a proxy for severe disability in AD, although an imperfect one."
In his presentation to the HCFA meeting, Small said that the use of cholinesterase inhibitors results in significant improvement in memory and other cognitive functions in mild to moderate cases of AD. By stabilizing and delaying the functional decline, he added, patients can maintain autonomy longer and nursing home admissions can be delayed, resulting in both cost savings and less of a burden on caregivers.
In addition to AD and other forms of dementia, researchers are now using PET scans to determine whether or not a patient has a deficiency in dopamine synthesis in the brain, indicating the presence of Parkinson's disease. Parkinson's patients show decreased activity in the basal ganglia region of the brain. Post-transplant PET scans are used to monitor the effectiveness of fetal dopamine-synthesizing cells implanted surgically. And PET is also used to identify regions of reduced glucose metabolism and to pinpoint epileptogenic tissue, which can be removed surgically, in children with seizures.
In addition, PET can be used to grade the degree of malignancy in brain tumors, to determine the degree and extent of brain damage following a stroke, to differentiate unipolar from bipolar depression and to differentiate chronic depression from AD.
PET is widely used in diagnosing a number of cancers. For example, it can be used to differentiate tumor from scar, to image metastases of advanced thyroid carcinoma, and to detect primary and recurrent or residual musculoskeletal tumors and to monitor response to therapy. It also can be used be used to detect primary breast cancer in patients with breasts that are difficult to evaluate with mammography. It can help determine the extent of disease in patients with breast cancer and monitor the effectiveness of therapy.
In cardiology, it can be used to define areas of myocardial ischemia, to diagnose and localize myocardial infarction, to detect coronary artery disease and identify individual, stenosed vessels both at rest and during stress. PET studies can be used for cardiac wall motion assessment, determining the viability and potential reversibility of dysfunctional myocardial segments and assessing perfusion.
Following cardiac bypass surgery, PET is used to evaluate the effect of the surgery on myocardial perfusion and metabolism. It also is used in percutaneous transluminal coronary angioplasty assessment to differentiate ischemia, viable myocardium that responds to revascularization and assess the recovery of metabolism in the ischemic area.
But despite its broad range of uses, PET continues to be classified as experimental, except for lung cancer, which makes the outcome of the HCFA assessment procedure most crucial.