Measurement of White Matter Structure Changes in Amyotrophic Lateral Sclerosis Using Fractal Analysis

Amyotrophic lateral sclerosis (ALS) is recognized as a motor neuron disorder affecting the structure and function of the brain and neuromuscular system. Very little is known, however, that the nervous system degeneration is dependent on disease phenotypes of ALS. The purpose of this study was to determine the degree of brain white matter (WM) structure degeneration in four ALS patient groups characterized by their clinical signs and neuroimaging measurements. Fractal dimension (FD) of three-dimensional (3D) brain WM images was quantitatively analyzed to evaluate the WM structural complexity, including complexity levels of the WM skeleton, surface and general structures in ALS patients and control subjects. A total of 100 participants were assigned into five groups: ALS patients with frontotemporal dementia (ALS-FTD, n=20), ALS patients with predominantly upper motor neuron (UMN) signs and hyperintensity MRI signals on corticospinal tract (CST) (UMN-CST + , n=20), ALS patients with predominantly UMN signs but without hyperintensity signal on CST (UMN-CST-, n=27), ALS patients with an equal amount of UMN and lower motor neuron (LMN) signs (ALS-classic, n=22), and a neurological control group (n=11). The brain was extracted