Motor neuron disease (MND) is a progressive neurological disorder that destroys the cells which control voluntary muscle movements such as walking, breathing and speaking. Normally, the signals are transmitted from the nerve cells in the brain to the brain stem and the spinal cord which are then sent to various muscles. The upper motor neurons are responsible for the controlling of movements such as walking and the lower motor neurons control the movements of the arms, legs, chest and face. When the disruptions of the signals happen, the muscles may not function properly continuing to weaken and waste away causing uncontrolled twitching. When the signaling process between the upper and lower motor neurons occurs, it can result in limb stiffness and the tendon reflexes such as the knee-jerks can become overactive. Progressively, the control of voluntary movements of the affected individual can also become lost. MND commonly affects individuals in their mid-50s with the survival rate of around 2-5 years from the time the symptoms develop.
Causes
This condition develops when the nerve cells (motor neurones) in the brain and the spinal cord lose their function. In most cases, it does not present a family history of the condition although around 5% of individuals have a close family relative with this disease. Some of the possible causes include abnormal clumps of protein that occurs inside motor neurones, disruption of the transport system in the motor neurones, problems with the glial cells that support motor neurones providing them with nutrients and abnormal mitochondria in the motor neurones.
Types of motor neuron disease
Amyotrophic lateral sclerosis is the common form of MND which involves the upper and the lower motor neurone and is characterized by the weakness and the wasting of the limbs. The average life expectancy is around 2 to 5 years from onset of symptoms.
Progressive bulbar palsy involves both the upper and the lower motor neurones presenting symptoms such as slurring of speech and difficulty swallowing. The average life expectancy is around six months and three years from the initial onset of symptoms.
Progressive muscular atrophy mainly affects the lower motor neurones with symptoms such as weakness or clumsiness of the hand. The life expectancy can extend to more than five years in most of the cases.
Primary lateral sclerosis is a rare form involving the upper motor neurones presenting weakness of the lower limbs. The life expectancy can be normal but can be life-limiting.
Diagnosis
The diagnosis is possible based on the symptoms evident and the physical examination by a neurologist. Additional tests may include blood tests, MRI scan, electromyography that measures the electrical activity of the muscles, nerve conduction test and a muscle biopsy.
Treatment
There is no cure for MND but the treatment can provide relief from the symptoms and to slow the progression of the disease. The treatment to relieve the symptoms includes physiotherapy to help with muscle cramps and medications to treat muscle stiffness, drooling and provide pain relief. A language therapist can help teach techniques for communication difficulties. In the case of swallowing problems, a feeding tube may be implanted into the stomach to provide nutrition.
References
http://www.nhs.uk/Conditions/Motor-neurone-disease/Pages/Treatment.aspx
http://imnda.ie/about-mnd/common-symptoms-and-effects-of-mnd/
https://www.neura.edu.au/health/motor-neurone-disease/
