Mapping the size of the sensory nerves in familial dysautonomia

The 12 cranial nerves carry bundles of fibers that enter and exit the brainstem at various levels. The trigeminal nerve is the largest of these nerves and provides the brain with sensory information from the face, scalp, and throat. It controls how often we blink, tear, how we bite, and chew. Each of these things we take for granted are impaired, to varying degrees, in patients with familial dysautonomia (FD).

Brain MRI scans are common in patients with neurological illness and are used by clinicians to investigate a whole host of neurological complaints from seizures to headaches. Over the years, the Center has collected routine MRI scans of the brain from patients with FD and stored them with the hope of being able to understand which particular areas are affected.

 imaging the brain can be a potentially useful way to measure response to treatment when new therapies are being tested.

Using magnetic fields, we can collect an image of the brain at various levels. The images can create a picture of the brain’s contours so you can see structures. The structures in different regions provide a measure of the density of neurons. Not only are they a diagnostic tool, brain MRIs are frequently used in clinical trials to monitor rates of neuronal degeneration.

In collaboration with the Department of Radiology at NYU, the Dysautonomia Center embarked on a study to look at the size of the trigeminal nerve in patients with FD. “We had some key questions,” explained Dr. Kaufmann, “We wanted to know what happens to the nerve and if it changes overtime”. Using routine clinical MRI scans, the team carefully analyzed each of the scans and measured the morphology of the trigeminal ganglia.

UnknownOver the years, they built up enough information to compare the scans acquired from FD patients to those in normal controls. When a healthy brain develops, the trigeminal nerve cells bundle together into a ganglia, which is particularly large and amenable to imaging. There are ganglia on both sides that bring connections from the head and neck. In an MRI scan it is possible to locate the trigeminal nerves, map the blurry edges, and measure their dimensions to calculate the area. Larger areas indicate more nerves.

What we saw in patients with FD was quite remarkable. The size of the trigeminal nerves was much smaller in the patients than in controls. This difference remained even when normalizing for body mass. The trigeminal nerves were about half the size. In addition to having smaller nerves, the patients all had signs and symptoms of loss of trigeminal sensations, including lack of tearing, corneal injuries, and swallowing difficulties. They were, however, no differences in the caliber of the nerves with age.

“The findings are encouraging, we are always looking for non-invasive ways to follow the health of the nerves.  Here you have an image of the nerves themselves measurable in a conventional MRI” – Dr. Alberto Palma

The idea that the nerves aren’t deteriorating at a rapid rate and appear stable is also important. When looking at the impact of new therapies investigators will need to assess whether they are saving the nerves from an ongoing atrophy or re-growing them. Finding good biomarkers for patients with FD is an important initiative.

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