Jan 21 (Reuters) - Alzheimer"s patient groups, disappointed by Medicare"s plan to sharply limit coverage of new drugs for the brain-wasting disease, are planning publicity and lobbying campaigns to protest a proposal they say could delay their use for 10 years. "Congress has to know how bad this will be for patients," said John Dwyer, president of Global Alzheimer"s Platform Foundation (GAP) advocacy group. In a preliminary decision last week, the U.S. Centers for Medicaid and Medicare Services (CMS), which runs the government health plan for people age 65 and older, said it would cover Biogen Inc"s (BIIB.O) already approved Aduhelm, and similar Alzheimer"s disease treatments in development, only for patients enrolled in approved clinical trials. That plan would severely limit the number of patients receiving the treatment, undercutting the Food and Drug Administration"s accelerated approval of Aduhelm for patients in the early stages of the memory-robbing condition. The public disagreement over the drug"s use is unusual for the agencies, both part of the U.S. Department of Health and Human Services. Alzheimer"s Association Chief Executive Harry Johns said Medicare"s plan "usurps FDA"s role in drug approvals," calling it "an unprecedented and terrible draft decision." His group, as well as UsAgainstAlzheimer"s and GAP - three of the biggest Alzheimer patient organizations - said they plan to fight the decision by appealing to lawmakers, the Biden administration and the U.S. Health Secretary. The Alzheimer"s Association said it is using "all avenues of communication" to make its case. Biogen is also fighting the decision and in a statement said it is "supportive of the community in raising their voices on this important issue of access." The Medicare agency could alter its plan before it is finalized in April, but it is unclear what new evidence or facts would cause it to soften its stance. "There are only two clinical studies ... There isn"t any real-world experience to convince CMS," said James Chambers, a researcher at the Center for the Evaluation of Value and Risk in Health at Tufts Medical Center in Boston. "They will receive a lot of outrage as opposed to new information." Medicare has opened a 30-day comment period with a final decision due by April 11. "If the (CMS) decision changes, it will be because of political pressure," said Raymond James analyst Chris Meekins. CONTROVERSIAL DECISION The FDA"s June decision was the first approval of an Alzheimer"s drug in nearly two decades, but was a controversial one not supported by the agency"s outside advisers. It relied on evidence that the drug can reduce amyloid brain plaques, a likely contributor to Alzheimer"s, rather than proof that it slows progression of the disease. Only one of Biogen"s two large-scale trials showed that Aduhelm had an impact on cognition. The three Alzheimer"s patient groups said Medicare"s plan unfairly penalizes people with the disease - probably because there are so many of them and the cost could be enormous. Aduhelm"s price - cut recently to $28,200 from $56,000 per year - sparked concerns about Medicare"s budget since Alzheimer"s is an age-related disease and around 85% of people eligible for the drug are in the government plan. The number of Americans with Alzheimer"s is expected to rise to 13 million by 2050 from more than 6 million currently. Biogen has estimated that around 1 million would currently be eligible for Aduhelm. Other companies, including Biogen partner Eisai Co Ltd and Eli Lilly and Co (LLY.N), also are pursuing accelerated approval from the FDA for similar medications. "This decision was not about Aduhelm alone. This was a decision about drugs still in trials," said UsAgainstAlzheimer"s chairman George Vradenburg. "It is stunning preemption." Medicare typically pays for FDA-authorized medications, but by law is required to cover only products and services deemed "reasonable and necessary" for diagnosis or treatment. Vradenburg said his organization is "communicating with Congress and the Biden Administration" about its dismay. (This story corrects paragraph 13. Chris Meekins is a healthcare policy analyst at Raymond James, not Leerink.)