Frontal lobe atrophy in motor neuron diseases

Area of Science:

• Neuroscience
• Neurology
• Radiology

Background:

• Spastic paresis in motor neuron diseases is not solely explained by precentral gyrus degeneration.
• Amyotrophic lateral sclerosis (ALS) and primary lateral sclerosis (PLS) are distinct motor neuron diseases with differing pathological features.
• Cortical and white matter changes in the frontal lobes may contribute to the clinical presentation of these diseases.

Purpose of the Study:

• To investigate extensive cortical atrophy in the frontal and parietal lobes in patients with ALS and PLS.
• To compare brain MRI measurements between ALS patients, PLS patients, and healthy controls.
• To correlate observed brain changes with the clinical syndromes of upper motor neuron degeneration.

Main Methods:

• Magnetic Resonance Imaging (MRI) was used to measure the surface area of the precentral gyri and underlying white matter in the frontal and parietal lobes.
• The study included 11 sporadic cases of classical ALS, 8 patients with PLS, and 49 age- and sex-matched healthy controls.
• Patients with overt dementia or other mental diseases were excluded.

Main Results:

• Primary lateral sclerosis (PLS) showed significant atrophy of the precentral gyri and underlying white matter (approx. 75% of normal).
• Anterior frontal cortical surface area was reduced in PLS (approx. 85% of controls) with corresponding white matter loss.
• Amyotrophic lateral sclerosis (ALS) showed no significant frontal cortical atrophy but significant white matter reduction, comparable to PLS.

Conclusions:

• In PLS, widespread frontal lobe atrophy, including motor, premotor, and supplementary motor areas, explains the progressive upper motor neuron syndrome.
• In ALS, white matter shrinkage suggests axonal degeneration from sources other than the frontal cortex, potentially explaining cognitive deficits.
• Age-related frontal lobe shrinkage is less pronounced than the atrophy observed in ALS and PLS.