Morrie suffers from ALS, also known as "Lou Gehrig's Disease," which is a disease which affects the neurological system. Though the book would likely not be classified as "medical" or even "scientific" in nature, what one could glean from reading it is a personal understanding of what a person suffering from this disease is likely to go through. Though there are no major scientific or medical explanations, there is a very personal account from Mitch Albom about the changes he notices his professor going through.
These changes include the slow muscle degeneration which starts with the loss of Morrie's ability to dance, followed by his inability to press the brake pedal (and therefore his ability to drive) and finally the loss of his ability to walk. He progresses to requiring assistance in the bathroom and later uses a catheter bag. He needs assistance with everything from getting dressed to eating.
As the disease progresses, Morrie has more and more trouble breathing. He is hooked up to oxygen. He speaks more slowly. He develops a terrible wracking cough that brings up a lot of phlegm and keeps him awake at night. He requires more sleep and gets tired much sooner.
Essentially, what this book shows about ALS, is its slow progression of deterioration on the body. For most, this is also a deterioration of will, independence, and often times, self-dignity. But for Morrie, this book highlights the way the disease was not allowed to take his spirit and though it is neither scientific nor medical in tone, this book could provide encouragement for someone who has a loved one suffering from ALS.