Calculating Odds of ALS Diagnosis

[BriBriBB]

now my math could be wrong but since I was bored, using an estimate of 289,000,000 people in the U.S. and also using estimate of about 5000 people in the U.S. are diagnosed with ALS in a year, and of those 6.7% have twitches as their first and only symptom I came up with these odds.

0.00001730% chance of someone having ALS.
and then out of those 6.7% have twitches alone the odds are 0.00000258% that you have ALS.

 

[Weegidy73]

Brian,

It's not quite that simple. I wouldn't have come up with the stat issue again, but since you asked the question, let me try to answer it:

of course you are right with your calculations, this is the very low probability that anyone out of the GENERAL population will get "twitch-onset" ALS.

However, for a person who suddenly develop twitching we can no longer
take the general population as a basis. Here comes conditional probability
into play. For this person, the real question is: "How are the odds of ALS,
given the fact that I already have one of the symptoms (i.e widespread
twitching) Now we must take as "basis population" the subgroup of twitchers instead of the whole population.
(That's why it would be so important to know the actual frequency of BFS
in the population)

Fortunately, though, it is reasonable to assume that BFS is indeed quite common, (my own estimate would be about 1 Percent)
So we could take the 2,890,000 twitchers (out of 289,000,000 general population) as the basis which leads to a higher but still very reassuring low odds for ALS.

Furthermore, if you factor in other facts like clean EMG and neuro exam,
then, of course, the odds are still much lower

Let me add that this post is really not meant to sound priggish/know-it-all-ish (I hope it isn't perceived in that way I just wanted to clarify the so-often misunderstood issue about (conditional) probability...

 

[LetsGoBucs]

Asterix,
Actually, I called a neuro about this issue, I am a little neurotic. He said that in his case fasics with out the presence of clinical weakness doesn't make your chances of having ALS higher it makes them lower. He said that if twitching is found without clinical weakness, than your chances are less than the average person who does not know or think about whether they have weakness or not. He assured me that FASICS WITHOUT WEAKNESS is never ALS. He said that the 6.7% may have had slight weakness, but it was there. They wouldn't have presented with a twitch in this finger, and than a twitch in their stomache, and than a twitch in their toe, it is very rare for ALS to present like that. He said that ALS almost always presents with weakness and fasics in a confined area, and than the fasics move as the weakness does. It is most rare to find an ALS patient with widespread fasics in the beginning stages of ALS. Also my neuro didn't say this, but for the young people out there (under 30) the chances of you having ALS twitching or not, are ASTRONOMICAL if you do not have the familial trait in your families. My research shows that almost always those diagnosed at 20 and 25 are diagnosed with the familial form. Hope this helps.

 

[emurray1]

Great info Guest!! Twitching with no weakness=NO ALS. Its that simple. I have been twitching for 6 months, no weakness, plus I am 27. I have no worries. Forget the stats go on how you feel.

 

[dylan.dibber1]

Great stuff, especially in view of the always creepy 6.7% study being posted in another topic

I know not everyone here is under 40, but those of you who are can indeed take even more comfort that the odds against non-familial ALS are astronomical.

Even amongst the infamous 6.7% of ALS sufferers who presented with fascics only (in one study), NONE were abnormally young (I think the study said mean age around 53 plus or minus 12 years). Even the authors of that letter, who were urging caution, were urging it specifically for either people over 45 or people with ALS in their families.

 

[emurray1]

what's the deal with familial als? my grandfather's brother had als at the age of 70 something. how is that related? i'd look online myself, but i don't trust myself with any sites about als.

 

[GypsyDuBois]

7tidalwave (gosh it's hard remembering how to type your name!)

I just re-read the survey and saw that you've been having your fascics for 2 years. I really, really, really don't think you have much to worry about, regardless of family history. ALS does its whole thing inside 5 years in the majority of cases. By 2 years you'd be facing some significant weakness. I think you're off the hook buddy. Relax!

 

[Alonzo]

thanks jblack. i don't worry so much during the day, but i was up too late last night and really overtired. it seems like however much confidence i gain, it doesn't take that much to make me worry. thanks for the quick reply.