A new study suggests that a simple eye exam and retinal imaging test may help improve the diagnostic accuracy of frontotemporal degeneration (FTD), a disease which causes progressive damage to the temporal and/or frontal lobes of the brain.
FTD is often misdiagnosed as Alzheimer’s or vice versa but there are some key differences between the two. For example, FTD typically manifests as a gradual decline in behavior and/or language, but unlike Alzheimer’s, memory is often well-preserved. In addition, onset of FTD usually occurs in a person’s 50s and 60s, although it has been seen as early as 21 and as late as 80 years. Alzheimer’s typically begins after age 65.
For the study, researchers from the Perelman School of Medicine at the University of Pennsylvania used an inexpensive, non-invasive, eye-imaging technique. They found that patients with FTD showed thinning of the outer retina (the layers with the photoreceptors through which we see) compared to control subjects.
The retina is potentially affected by neurodegenerative disorders because it is a projection of the brain. Previous research has shown that patients with Alzheimer’s disease and ALS (amyotrophic lateral sclerosis) may also have thinning of the retina — although in a different part of the retina. Imaging the retina may help doctors confirm or rule out FTD.
“Our finding of outer retina thinning in this carefully designed study suggests that specific brain pathologies may be mirrored by specific retinal abnormalities, said study lead author Benjamin J. Kim, M.D., assistant professor of ophthalmology at Penn’s Scheie Eye Institute.
In general, neurodegenerative disease are challenging to diagnose, and often are confirmed only by direct examination of brain tissue at autopsy. Now that science appears to be on the brink of developing effective treatments for these diseases, the need for better diagnostic methods is becoming extremely important.
“As we enter an era of disease-modifying treatments for neurodegenerative disorders, it is essential for us to have tools that can identify the specific pathologies accumulating in the brain so that we can administer the appropriate treatments to patients who are likely to benefit,” said study senior author Murray Grossman, M.D., a professor of neurology and director of the Penn FTD Center.
The study involved 38 FTD patients and 44 healthy control subjects. The FTD patients were carefully evaluated with clinical exams, cerebrospinal fluid biomarkers to exclude Alzheimer’s disease and genetic testing.
The researchers then used a non-invasive eye-imaging technology called spectral-domain optical coherence tomography (SD-OCT), which uses a safe light beam to image tissue with micron-level resolution.
Measurements of the retinal layers showed that the outer retinas of the FTD patients were thinner than those in the control subjects. This relative thinning of outer retinas was caused by a thinning of two specific portions of the outer retina: the outer nuclear layer (ONL) and ellipsoid zone (EZ). The ONL of FTD patients was about 10 percent thinner than controls, and this ONL thinning was the primary source of the outer retina thinning.
In addition, the severity of retinal thinning among FTD patients tended to be worse when the patients’ scores on a standard cognition test were lower.
The findings are published in the journal Neurology.