Motor-neuron disease (MND) is a class of disorders that affect the motor neurons and results in marked muscle weakness, loss of muscle bulk (atrophy), and often tiny muscle twitches known as fasciculation. The cause of MND is not known, but these conditions selectively attack motor neurons, the nerve cells that control muscle movement, while sparing the sensory systems. There are two main types of motor neurons. The “upper motor neurons” live in an area of the brain just in front of a major groove called the central sulcus, and send their axon fibers down the spinal cord. These fibers send information to the “lower motor neurons” that directly contact the muscles. Loss of the lower motor neurons causes weakness and atrophy of the muscles and twitches called fasciculation. Loss of the upper motor neurons leads to decreased coordination for skilled tasks, stiffness, and spasticity, and increased (“brisk”) spinal reflexes.
The most widely known MND is amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig’s disease, in which both upper and lower motor neurons are affected. Other forms include primary lateral sclerosis (PLS), which affects primarily the upper motor neurons and often has a less severe course than ALS, and progressive muscular atrophy (PMA), which primarily affects the lower motor neurons. MND is considered neurodegenerative with gradual progression and severe disability, often leading to death in a few years. If an MND is suspected, you should see a neuromuscular specialist who will order or perform an EMG which can confirm or exclude the diagnosis. Sometimes other conditions can mimic MND. If you have MND, regular visits to your neuromuscular specialist are important. Since the disease can progress rapidly, changes in breathing, speech and swallowing function can occur and require supportive treatments. Although this is a progressive and incurable disease at the present time, there have been significant improvements in survival and quality of life, mostly associated with better supportive treatments such as gastrostomy tubes and non-invasive ventilation. Riluzole and edaravone are medications FDA approved for the treatment of MND and are associated with a modest extension of life expectancy. There are many ongoing clinical trials being conducted around the world to find new treatments for this condition.