Motor Neurone Disease
Symptoms
- Weakness.
- Muscle wasting.
- Twitching of the muscles (fasciculation). The weakness may start in a limb or in muscles necessary for speech or swallowing (bulbar).
- Respiratory muscle involvement is usually later.
Diagnosis
The full pattern may not be present initially but the characteristic pattern of muscle weakness with signs of both upper motor neurone and lower motor neurone involvement and the lack of involvement of sensory nerves, bladder function or eye muscle involvement will particularly, if a lot of fasciculation is present, be important clues to the examining Neurologist.
Electromyography and nerve conduction studies are important to confirm the lower motor neurone involvement in some cases and to rule out motor neuropathy, some of which are treatable. Scans cannot positively identify Motor Neurone Disease but may be necessary to rule out other possibilities. With a bulbar presentation, the usual chief differential diagnosis is Myasthenia Gravis.
With limb involvement, trapped nerves rarely from tumours but sometimes from degenerative disease of the spine may cause difficulty and if all signs are lower motor neurone, motor neuropathies which can on occasion respond to suppression of the immune system can cause some diagnostic difficulties.
Cause
Very rarely is the cause genetic. A few genetic mutations have been discovered, all affecting a protein known as SOD-1. Age is a risk factor as it becomes increasingly common with each decade.
In 99% of cases, the cause is unknown.
Effect
The motor nerve cells that travel from the motor cortex down through the bulbar region to the spinal cord degenerate. So do the nerves that pass from the spinal cord out to the muscles. This causes upper motor neurone signs by way of increased reflexes and usually mild spasticity. The lower motor neurone component causes the muscle wasting and fasciculation. It is the combination of the upper and lower motor neurone signs and the pattern of muscles that are affected particularly bulbar muscles that are rare with other neurological conditions and help make the diagnosis. The nerve cells degenerate in a progressive manner. The illness is generally serious with progression of the weakness so although there is a wide-spread, the average time to terminal care is around 3-4 years. The mechanism of the cell death is uncertain but may involve the neuro-transmitter, glutamate. Accumulation of protein inparticular SOD-1 at least in some patients may be important.
Treatment
Largely supportive. A drug is available (Riluzole). This is felt to have a slight effect on slowing down the disease process. However, more important at the moment is a multi disciplinary care package with good education, physician support with significant need for physiotherapy, occupational therapy and speech therapy input and later rehabilitation expertise and terminal care.
Some patients with swallowing problems that become significant will need tube feeding through a gastrostomy or more rarely, trans-nasally. A few patients elect for respiratory support.
In some patients, anti spasticity agents and pain relief is important.
