99% Certainty

Yesterday someone posted an Anonymous comment in my blog about Hope asking "Is the test for ALS definitive?" That is an interesting question to ask. It speaks to me of the search for hope, of the possibility that the doctors might be incorrect. It's the very question I asked when I was first given this dreadful diagnosis. The neurologist freely admitted that they might be wrong. It happens. When I asked how often, I got the real story. My neurologist said that they were more than 99% certain.

The problem is that there is no "definitive" test for ALS; no blood test, no DNA test, no muscle test nor biopsy test. Nothing. So how do they know? How do they test for a disease when there is no actual definitive test for the disease? They do it through what is called a "clinical diagnosis".

A clinical diagnosis is one where the presence, or absence, of a particular disease or condition is determined by the existence of symptoms and the determination that all other potential causes for the symptoms are not present. In other words in an ALS clinical diagnosis, they look at your symptoms and rule out every other possibility for the cause.

They start with a physical examination focused on the area of muscle loss, looking specifically at muscle control, muscle loss and fasciculations. Then they do reflex testing to determine if your reflexes are normal. They run all kinds of blood tests and urine tests. They do full body MRI scans and take x-rays of your brain. The results of these tests provide the neurologists with a range of possible suspects.

The next step is to narrow that range, first with more blood tests, additional MRI's, and then with physical torture. Well, it feels like physical torture. Once they get to the point where they suspect denervation, they test the nerves. This typically takes the form of a nerve conduction velocity (NCV) test and a session of Electromyography (EMG). Both of these involve pain.

With the NCV test, a technician hooks up electrodes to your skin, one at the top of the target nerve system and the other at the bottom of the target nerve system. In my case it was my legs. The the technician shoots an electrical charge through your nerves to see how long it takes to get from one end of the nerve to the other end of the nerve. Basically they electrocute you with enough of a charge to test the nerve but not enough to kill you. It is also enough of a charge to cause various other muscles to release that which they hold back. It's a messy outcome.

The EMG is even more exciting. Since this is a more challenging test, it is performed by a doctor and is often done more than once. It was twice in my case, once by the muscle specialist and the second time by the neurologist. The doctor pushes a long needle into the target muscle and nerve area. Then the needle is wiggled about to touch the end of the motor nerve servicing the muscle. Then you are asked to not move while the doctor wiggles the needle some more to see if the nerve is working properly.

Remember, through all of this it is only the motor nerves that are dying. Your sensory nerves, the ones that feel pain, all work just fine. It hurts, a lot.

After doing all this, the neurologist looks at the results. If there is nothing else causing the denervation and loss of muscle, then it is ruled as "probable ALS". The ultimate, final, definitive diagnosis of ALS can only be made by autopsy, by inspecting the nerves after death. I am not going to bother with that part. I think a certainly level of 99% is sufficient for me.