Motor neuron disease (MND) is a rapidly progressing neurological disease that destroys motor neurons, causing them to stop working properly. Motor neurons are the cells responsible to control primary muscle activity, which includes breathing, speaking, swallowing, and walking. Generally, messages from nerve cells in the brain (upper motor neurons) are transferred to nerve cells in the brain stem and spinal cord (lower motor neurons), then the messages are transmitted from lower motor neurons to particular muscles. When there are disruptions in the signals between the lower motor neurons and the muscle, the muscle will not work properly, it will progressively decline and may begin to deteriorate.
Most people who develop motor neuron disease usually have no family history of the condition. It is also very unlikely to develop in other family members. However, the disease has inherited forms, which appear in children, and the symptoms can be present at birth. It can also occur at any age, but in adults, the symptoms usually appear after the age of 40. There are several types of motor neuron disease. Doctors classify the disease according to whether they are inherited or sporadic.
- The most common MND in adults is amyotrophic lateral sclerosis (ASL) that affects both the upper and lower motor neuron. Muscles of the arms, legs, mouth, and respiratory system can be affected.
- Progressive bulbar palsy (PBP) involves the brain stem. Usually, people with ALS have PBP too. It causes frequent choking spells, difficulty eating, swallowing, and speaking.
- The rarest form of MND is the primary lateral sclerosis, which affects the neuron in the brain. It is not fatal, but it can seriously disturb a person’s life.
- Progressive muscular atrophy (PMA) affects the lower motor neurons in the spinal cord. It is one of the rarest conditions which causes slow but progressive muscle wasting.
- Spinal muscular atrophy (SMA) is an inherited MND, and it affects children. This condition tends to affect the legs, arm, and trunk.
The symptoms of MND begin regularly over weeks and months. It usually takes place on one side of the body and then gets gradually worse. The common early symptoms are a weakened grip, slurred speech, dragging of the leg, weak ankle muscles, and weakness at the shoulder. The condition is mostly not painful. As the damage is progressing, it will extend to other parts of the body until the person is eventually unable to move.
Little is known about the exact causes of motor neuron disease. Experts believe that 90% of MNDs happen randomly (not currently known), and the other 10% are hereditary. According to the National Institute of Neurological Disorders and Stroke, sporadic or inherited MNDs may be implicated by environmental, toxic, viral, or genetic factors. Doctors also often find it tough to diagnose MND, particularly in the early stages since it can resemble other conditions like multiple sclerosis. When a doctor suspects someone has MND, they will typically refer them to a neurologist and suggest a thorough examination and tests, including blood and urine tests, MRI brain scan, muscle biopsy, electromyography (EMG), or spinal tap.
MND does not have a cure yet, but the right treatment may slow its progression. The treatments usually involve supportive devices and physical therapy. For some types of MND, the disease progression can also be slowed down by drugs. New medications are emerging, and researchers are investigating many options in hope to produce a cure. And although it is still unclear what causes motor neurons to stop working properly, better knowledge of genetic factors might prevent inherited MND.