In a sign of the continuing difficulty of obtaining patent protection for medical diagnostic methods since the Supreme Court’s 2012 decision in Mayo Collaborative Servs. v. Prometheus Labs., Inc. (see summary here and here), the Patent Trial and Appeal Board (PTAB) of the U.S. Patent and Trademark Office (PTO) recently affirmed a patent examiner’s rejection of a patent claiming a method for diagnosing Alzheimer’s disease. The patent application is owned by Eisai R&D Management Co., Ltd., a subsidiary of the Japanese pharmaceutical company Eisai Co., Ltd. (“Eisai”). The application claims administering lidocaine, a local anesthetic, to a patient suspected of having Alzheimer’s disease then measuring levels of lidocaine or a metabolite thereof in the patent’s cerebrospinal fluid. Levels of lidocaine or its metabolite below levels seen in healthy control subjects indicates that the patient has Alzheimer’s disease.