Charting the course of PLS and PMA

Primary Lateral Sclerosis (PLS) and Progressive Muscular Atrophy (PMA) are two rare variants of the disease ALS. Normally, ALS affects the upper motor neurons in the brain and spinal cord, as well as the lower motor neurons that send signals from the spinal cord directly to muscles. PLS and PMA are different because PLS only affects the upper motor neurons, and PMA only affects the lower motor neurons. It’s an important distinction for patients to be told about because the prognosis is less severe in these conditions.  On average, survival in ALS is typically reported to be 2-5 years, whereas for patients with PMA it’s more like 5-10 years and for PLS it’s even longer (often several decades).

ALS itself is a rare condition, affecting some 30,000 people in the United States at any one time.  PLS and PMA each represent approximately 5% of the overall ALS community, so there’s approximately 1,500 patients with each condition in the U.S at any given time.  In April 2008, PatientsLikeMe added the ability for members of our ALS community to change their diagnosis to these rare conditions.  To date, we now have 182 patients with PLS and 270 with PMA. This is truly exciting because even the largest studies in the literature have only examined 40 or so PLS patients and a similar number of PMA patients. One of our most useful features on our site for people with ALS is the percentile curves, which we display as a backdrop on their profiles to put each individual’s rate of progression into context. However, as you can see in the figure below, when you compare the progression curves of ALS patients on our site with those of a typical PLS patient, the PLS patient progression deviates significantly from the ALS curves.


With so many PLS and PMA patients sharing such valuable information about their disease on PatientsLikeMe, we had enough information to generate a new set of percentile curves for each of those communities.  To do this, we used self-report ALSFRS-R (ALS functional rating score – revised) data from 104 PLS patients and 59 PMA patients that met our criteria for data quality. We have good data for the first 4-5 years of disease after onset, and after that point we rely on linear extrapolation to make the plots.  Here we see the value of openness in action.  When you see the potential value in contributing your data, it drives a virtuous cycle: the more data you enter, the more value you get, so you enter more data!


As any of our patients in these communities will tell you, being diagnosed with a rare disease can be a frustrating experience. Aside from dealing with the condition itself, there’s the lack of public awareness, a lack of research investigating your condition, and a sense that you are being “lumped in” with a similar disease because your community doesn’t have the critical mass to merit its own attention.  These new percentile curves for PLS and PMA patients demonstrate the value and power of openness.  By sharing their health data in an open fashion, patients are providing new insights that are changing how we think and act when it comes to these very rare conditions.

Note:  A potential limitation of these curves is that they represent the outcomes for patients that are members of PatientsLikeMe and may not be generalizable to the entire population; we are working hard to better understand and correct for the biases in our population and data. As the size and longevity of each community increases, we will be in a better position to address these issues.

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9 thoughts on “Charting the course of PLS and PMA”

  1. Hi, very impressive! I hope you will expand to SMA soon, because i have been contacted by a lady whose child has this disease. Luckily it’s type II. thanks, Hans

  2. I have been in PLM since my dx 11/06 and have been considering my symptoms and I don’t seem to have at least yet the lmn symptoms of constant twitching and rapid muscle atrophy. I do have twitching at times but they don’t last more than a few minutes. I do have some muscle atrophy in my lower legs, but this is after 2 1/2 years. My weight has increased since dx do to lack of exercise, but I am thinking I have PLS. If I change my dx now will this screw up the data? What are the FRS scores going to do? etc?


  3. Russ – It’s always hard to tell exactly what is going on; the important thing is to be asssessed by a neurologist who is willing to consider that PLS and PMA are possibility alongside ALS. Some say you need to have a total absence of LMN signs for 3-5 years to be PLS, others have a different view. As you say, atrophy can be caused by immobility not just motor neuron function so it’s hard to work out. If you did change your dx (after speaking to your neurologist) then your data will be preserved and you will stay in the wider ALS community, you’d just get a different backdrop for your percentile curves and your stickman would change.

    Hans – Eventually it is our aim to have a community for every life-changing illness that exists. There are some unique challenges to illnesses where the patient is a child, and we would want to add some more family history / genetics tools to do SMA well, but yes, like all these unpleasant conditions it is on our radar screen. Thanks for your comment.

    Paul Wicks, PhD
    R&D Director, PatientsLikeMe

  4. Russ – I just realised that on my profile, somebody changed my diagnosis from ALS to PLS. From what I’m reading, I’m not sure that I disagree. But I’ve been twice diagnosed with ALS and that’s what I initially entered. What’s up?

    Look forward to hearing from you.



    1. Dear Jason,

      At the moment people who have had bulbar-onset ALS can record that in their profile and you can search for them using our advanced search feature. We haven’t yet looked into whether it would be useful to have separate percentile curves for bulbar-onset patients, good idea!

      Best wishes


  5. Mary Beth Rivetti

    This is very interesting. Last year my husband died 18 months after being diagnosed with Corticobasal degeneration. Autopsy of his brain tissue however revealed that he had Primary Lateral Sclerosis. His progression was probably much closer to ALS. The letter from the Mayo Clinic indicated that they had never studied someone presenting with asymmetrical involvement (which is why three neurologists concurred in the CBD diagnosis).

  6. There is very little on ‘straight’ PLS even on PUBMED. I feel that the symptoms list could be enlarged and refined a bit more, based on the reported symptoms on the Forums. And since the cause is not yet known, how about a medical history questionaire?
    For instance, vitamin D deficiencies. At 2 people so far have had them. What about autoimmune tests- I know I have had most of them. Allergies?, etc. I have copies of all my lab and test results, and probably alot of PLSers do.
    I’ve been trying to figure out how to make a forum questionaire, just to compare me with the other folks.
    I’d be happy to volunteer some time, especially if it would help add more knowledge about the disease.

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