The loss of pigmentation in the substantia nigra of the midbrain at the left in a patient with Parkinson's disease is contrasted with a normal midbrain at the right. Parkinson's disease is marked clinically by a "pill-rolling" tremor at rest, mask-like facies, and cogwheel rigidity of limbs, among other findings. Some cases occur in association with diffuse Lewy body disease, a form of dementia similar to Alzheimer's disease.

The apparent enlargement of the ventricles seen here is due to atrophy of the head of the caudate from neuronal loss with Huntington's disease, an autosomal dominant condition characterized clinically by choreiform movements.

Areas of the brain affected by AD

A = Cerebral Cortex

B = Basal Forebrain

C = Hippocampus

In this case of Alzheimer's disease, there is more marked atrophy seen superiorly and laterally, with sparing of the occipital region.

PET Scans

The characteristic microscopic findings of Alzheimer's disease include neuritic plaques ("senile plaques") which are extracellular deposits of the amyloid beta-protein (Aß). In the more numerous, smaller diffuse plaques this Aß alone is present as filamentous masses.

Amyotrophic lateral sclerosis (ALS) is uncommon. It usually begins in middle age and proceeds to death in several years. There is loss of anterior horn cells, so that patients present with progressive weakness that proceeds to paralysis from neurogenic muscular atrophy. Because of the loss of anterior horn cells, the anterior (ventral) spinal motor nerve roots with ALS demonstrate atrophy, as seen here in comparison with a normal spinal cord motor nerve roots.

Where are the anterior horn cells in this section of spinal cord? They are absent in a patient with amyotrophic lateral sclerosis (ALS).