Although PMA (Progressive Muscular Atrophy) was seen and noted by Doctors before ALS (Amyotrophic Lateral Sclerosis) it is much less widely known. Originally noted around 1850 it was originally called Aran–Duchenne muscular atrophy, Unfortunately, even today the medical establishment cannot decide whether to call PMA a subset of ALS or consider it a separate disease.
PMA is a motor neuron disease (MND) which affects ONLY the lower motor neurons (LMN). In some countries, Progressive Muscular Atrophy is called LMN predominant ALS and indeed, 20% of PMA sufferers will progress to full-on ALS.
I am not going to give a full clinical explanation because this has been done so much better by others.
What Is PMA?
In layman’s terms, lower motor neurons are the way the brain’s messages are sent from the brain stem, through the spinal cord to the voluntary muscles. When these motor neurons become damaged or eventually die, it prevents the muscles from firing properly and subsequently leads to muscle atrophy. Upper Motor Neurons originate in the brain and carry the impulses to the brain stem where they are passed off to the lower motor neurons. For a confirmed diagnosis of ALS most jurisdictions mandate that BOTH upper and lower motor neurons must be affected.
How is PMA diagnosed?
The quick answer is that very often, it isn’t. In other cases, PMA is misdiagnosed as ALS or many other variants thereof. Unfortunately, there is no hard and fast method for determining if a given patient has PMA. It is usually viewed as a diagnosis of exclusion. This means that once everything else has been eliminated, Progressive Muscular Atrophy emerges as the only solution left. In many cases, it can take years before a final diagnosis is confirmed. Even then, it can subsequently be determined that some other disease is really present.
How is PMA Treated?
There is currently no known cure for any type of motor neuron disease including PMA. The best the current state of medical knowledge can do is to manage symptoms. There are currently two recognised treatments for ALS – Rilutek and Edaravone which are routinely prescribed for PMA sufferers even though there were never trials specific to Progressive Muscular Atrophy. These drugs do not claim to cure motor neuron disease but have been shown to prolong life expectancy for SOME patients. There are a bunch of drugs that might be used to alleviate symptoms. The sad truth is that PMA, like most other motor neuron diseases, cannot easily be defined, categorised, diagnosed or treated.
What is the Prognosis for PMA Sufferers?
When I was initially personally diagnosed with Motor Neuron Disease in October of 2017, I was told that my life expectancy was between 2 – 5 years, which is the accepted norm for ALS patients. Even this is almost meaningless since there are so many different levels of progression. Some progress quickly and are well advanced before being diagnosed. Yet others live up to 20 years with varying levels of function. The one thing that seems clear is that, in general, PMA sufferers have longer survival rates. Most trustworthy sources quote an average life expectancy of 5 – 10 years with the same caveat as for ALS.
PMA by the Numbers
- ALS is already fairly rare: In Canada, it is estimated to occur to 1 in every 50,000 people. PMA accounts for approximately 5 – 7% of all Motor Neuron Disease patients.
- In my region of 1.5 million residents, there are currently (2019) only 3 known cases of PMA currently definitively diagnosed.
- Men are far more likely to be Diagnosed with PMA than women. Some estimate the ratio to be as high as 5:1.
- The average age at which PMA manifests is below 50.
- PMA is generally considered to be sporadic rather than hereditary, while almost 10% of ALS diagnoses are of the familial variety
For a more extensive explanation of PMA see the following document from the MND Association