Have You Seen This ‘New’ Memory Condition?

Patients experiencing memory problems often come to neurologist David Jones, MD, for second opinions. They repeat questions and sometimes misplace items. Their primary care clinician has suggested they may have Alzheimer’s disease or something else.

In many cases, Jones, a neurologist with Mayo Clinic in Rochester, Minnesota, performs a series of investigations and finds the patient instead has a different type of neurodegenerative syndrome, one that progresses slowly, seems limited chiefly to loss of memory, and which tests show affects only the limbic system.

The news of diagnosis can be reassuring to patients.

“Memory problems are not always Alzheimer’s disease,” Jones told Medscape Medical News. “It’s important to broaden the differential diagnosis and seek diagnostic clarity and precision for patients who experience problems with brain functioning later in life.”

Jones and his colleagues recently published clinical criteria for what they call limbic-predominant amnestic neurodegenerative syndrome (LANS).

Various underlying etiologies are known to cause degeneration of the limbic system, the most frequent being a buildup of deposits of the TAR DNA-binding protein 43 (TDP-43) protein referred to as limbic-predominant, age-related TDP-43 encephalopathy neuropathological change (LATE-NC). LATE-NC first involves the amygdala, followed by the hippocampus, and then the middle frontal gyrus, and is found in about 40% of autopsied brains in people over age of 85 years.

By contrast, amnestic syndromes originating from neocortical degeneration are largely caused by neuropathological changes from Alzheimer’s disease and often present with non-memory features.

Jones and his colleagues also classified a degree of certainty for LANS to use when making a diagnosis. Those with the highest likelihood meet all core, standard, and advanced features.

Patients with a high likelihood of having LANS meet core features, at least three standard features and one advanced feature; or meet core features, at least two standard features as well as two advanced features. Those with a moderate likelihood meet core features and at least three standard features or meet core features and at least two standard features and one advanced feature. Those with a low likelihood of LANS meet core features and two or fewer standard features.

To develop these criteria, the group screened 218 autopsied patients participating in databases for the Mayo Clinic Study of Aging and the multicenter Alzheimer’s Disease Neuroimaging Initiative. They conducted neuropathological assessments, reviewed MRI and PET scans of the brains, and studied fluid biomarkers from samples of cerebrospinal fluid.

In LANS, the neocortex exhibits normal function, Jones said. High-level language functions, visual spatial functions, and executive function are preserved, he said, and the disease stays mild for many years. LANS is highly associated with LATE, for which no biomarkers are yet available.

The National Institute on Aging in May 2023 held a workshop on LATE, and a consensus group was formed to publish criteria to help with the diagnosis. Many LANS criteria likely will be in that publication as well, Jones said.

Several steps lay ahead to improve the definition of LANS, the authors wrote, including conducting prospective studies and developing clinical tools that are sensitive and specific to its cognitive features. The development of in vivo diagnostic markers of TDP-43 pathology is needed to embed LANS into a disease state driven by LATE-NC, according to Jones’ group. Because LANS is newly defined, clinical trials are needed to determine the best treatments, he said.

“We are increasingly recognizing that the syndrome of dementia in older adults is heterogeneous,” said Sudha Seshadri, MD, DM, a behavioral neurologist and founding director of the Glenn Biggs Institute for Alzheimer’s and Neurodegenerative Diseases at the University of Texas Health Science Center at San Antonio, San Antonio.

LANS “is something that needs to be diagnosed early but also needs to be worked up in a nuanced manner, with assessment of the pattern of cognitive deficits, the pattern of brain shrinkage on MRI, and also how the disease progresses over, say, a year,” said Seshadri. “We need to have both some primary care physicians and geriatricians who are comfortable doing this kind of nuanced advising and others who may refer patients to behavioral neurologists, geriatricians, or psychiatrists who have that kind of expertise.”

About 10% of people presenting to dementia clinics potentially could fit the LANS definition, Seshadri said. Seshadri was not a coauthor of the classification article but sees patients in the clinic who fit this description.

“It may be that as we start more freely giving the diagnosis of a possible LANS, the proportion of people will go up,” Seshadri said.

Primary care physicians can use a variety of assessments to help diagnose dementias, she said. These include the Montreal Cognitive Assessment (MoCA), which takes about 10 minutes to administer, or an MRI to determine the level of hippocampal atrophy. Blood tests for p-tau 217 and other plasma tests can stratify risk and guide referrals to a neurologist. Clinicians also should look for reversible causes of memory complaints, she said, such as deficiencies in vitamin B12, folate, or the thyroid hormone.

“There aren’t enough behavioral neurologists around to work up every single person who has memory problems,” Seshadri said. “We really need to partner on educating and learning from our primary care partners as to what challenges they face, advocating for them to be able to address that, and then sharing what we know, because what we know is an evolving thing.”

Other tools primary care clinicians can use in the initial evaluation of dementia include the General Practitioner Assessment of Cognition and the Mini-Cog, as part of annual Medicare wellness visits or in response to patient or caregiver concerns about memory, said Allison Kaplan, MD, a family physician at Desert Grove Family Medical in Gilbert, Arizona, who coauthored a point-of-care guide for the American Academy of Family Physicians. Each of these tests takes just 3-4 minutes to administer.

If a patient has a positive result on the Mini-Cog or similar test, they should return for further dementia evaluation using the MoCA, Mini-Mental Status Exam, or Saint Louis University Mental Status examination, she said. Physicians also can order brain imaging and lab work, as Seshadri noted. Dementias often accompany some type of cardiovascular disease, which should be managed, Kaplan said.

Even if a patient or family member doesn’t express concern about memory, physicians can look for certain signs during medical visits.

“Patients will keep asking the same question, or you notice they’re having difficulty taking care of themselves, especially independent activities of daily living, which could clue you in to a dementia diagnosis,” she said.

The sources in this article disclosed no relevant financial relationships.

Karen Blum is a freelance medical/science writer in the Baltimore area.