ALS itself can be classified a few different ways: by how fast the disease progresses (slow vs fast progressors), by whether it is inherited or sporadic, and by where it starts. Most commonly (~70% of the time) the limbs are affected first. In this case, neurons in the brain (upper motor neurons) and in the spinal cord (lower motor neurons) are dying and this form is called ''limb onset''. In about 25% of cases, muscles in the face, mouth, and throat are affected first because motor neurons in the part of the brain stem called the medulla oblongata (formerly called the ''bulb'') start to die first along with lower motor neurons. This form is called ''bulbar onset''. In about 5% of cases muscles in the trunk of the body are affected first. In all cases the disease spreads and affects other regions. The symptoms may also be limited to one spinal region.

Can we conclude that in most cases does als affect the brain?
yes