Test predicts transition from normal to impaired cognition

The Stages of Objective Memory Impairment (SOMI) system predicted transitions from normal cognition to incident symptomatic cognitive impairment, longitudinal data showed.

Over an average follow-up of approximately 6 years, cognitively normal older adults whose memory test scores reflected moderate impairment in retrieval (SOMI-2) were twice as likely to progress to incident cognitive impairment as those whose memory was intact (SOMI-0), according to Ellen Grober, PhD, of the Albert Einstein College of Medicine in New York and co-authors.

Participants with memory storage deficits (SOMI-3 or SOMI-4) were three times more likely to progress, researchers reported in Neurology. After adjusting for all biomarkers, SOMI stage remained an independent predictor of incident cognitive impairment.

“There is mounting evidence that some people without thinking and memory problems may in fact show very subtle signs of early cognitive impairment,” Grober said in a statement.

“In our study, a sensitive and simple memory test predicted the risk of developing cognitive impairment in people who were otherwise considered to have normal cognition,” she added. “Our results support the use of the SOMI system to identify those most likely to develop cognitive impairment.”

Previous studies have linked SOMI scores to presence of Alzheimer’s disease pathology in people without cognitive impairment as part of the clinical trial on anti-amyloid treatment in asymptomatic Alzheimer’s disease (A4).

SOMI is based on the Free Cued Selective Recall Test (FCSRT). The test begins with a study phase in which people are shown four cards, each with drawings of four elements, and asked to identify an element that belongs to a particular category (for example, an apple would belong to the fruit category). Participants are then asked to recall the items; if they get stuck, they receive category hints to prompt them.

“The FCSRT provides measures of memory retrieval (free recall) and memory storage (total recall),” Grober and co-authors wrote. “Free recall scores predict incident mild cognitive impairment and incident dementia, particularly dementia due to Alzheimer’s disease, and often outperform other cognitive tests.”

The SOMI system maps free recall and total recall scores into steps. At SOMI-0, free recall and total recall are normal. SOMI-1 and SOMI-2 reflect increasing retrieval difficulty with decreasing free recall in the context of intact total recall, beginning 7–8 years before clinical dementia. In SOMI-3 and SOMI-4, cueing fails to retrieve all missed items in free recall, indicating a memory storage deficit occurring approximately 1–3 years before clinical dementia.

Grober and colleagues followed 969 cognitively normal people from Knight Alzheimer’s Disease Research Center in St. Louis who had a clinical evaluation of dementia (CDR) from 0 initially. The mean age was approximately 69 years, the mean follow-up was 6.36 years, and 59.6% were female.

About a third (33.8%) of participants were APOE4 positive. A total of 555 people had cerebrospinal fluid and structural MRI measurements (the biomarker subset) and 144 were amyloid positive. Results were adjusted for age, gender, education, and APOE4 Status.

Participants in SOMI-1 through SOMI-4 had elevated hazard ratios for transition from normal cognition to symptomatic cognitive impairment, defined as CDR ≥ 0.5.

SOMI-2 (HR 2.07, 95% CI 1.32-3.01) and SOMI-3/4 (HR 3.11, 95% CI 1.94-4.97) were significantly associated with incident cognitive impairment compared to SOMI-0 (P<0.001 for both). In subgroups with biomarkers and positive amyloid status, SOMI-1 participants also showed an increased risk of cognitive impairment.

In models including measures of amyloid and tau pathology and hippocampal volume, SOMI remained a significant predictor of time to CDR ≥ 0.5.

Only 4.9% of participants (47 people) were classified as SOMI-3 or SOMI-4, which limits the interpretation of data from this group, Grober and his co-authors said. Most of the participants were white and highly educated, and the results may not apply to others.