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Motor Neurone Disease.
Motor neurone disease is the name given to a group of related disease where the motor neurones degenerate causing weakness and wasting of the muscles. MND is a neurodegenerative disease which can potentially affect all muscle groups with only a small number being spared.
It is characterised by progressive degeneration of the anterior horn cells of the spinal cord, motor neurones in the brain stem and the corticospinal tracts, usually presenting as mixed upper and lower motor neurone signs with no sensory involvement. The anal and bladder sphincters are spared and the ocular motor muscles are also intact. The senses are not affected.
There are four main subtypes of MND
Amyotrophic Lateral Sclerosis (ALS) - This is the most common type of MND with approximately 65% of all cases in this catagory. It involves both the upper and lower motor neurones and so people may experience weakness, wasting and spasticity. People may aso experience emotional lability, weight loss and muscle twitches (fasciculations). The limbs, speech, swallowing and breathing may be affected. The average duration from onset of symptoms is approximately 2-5 years although this is variable.
Progressive Bulbar Palsy (PBP) - Approximately 25% of patients have this subtype of MND. Both the upper and lower motor neurones are affected in this type of MND. It is characterised by difficulty with speech and swallowing. There are no symptoms in the limbs. Breathing is affected by this type of MND and people may also experience emotional lability. The average duration from onset of symptoms is 6 months to 3 years.
Progressive Muscular Atrophy (PMA) - This subtype of MND affects approximately 10% of people. Only the lower motor neurones are affected in this type of MND which is characterised by muscle weakness and wasting. Weight loss and muscle twitches (fasciculations) may also occur. The average duration is over 5 years.
Primary Lateral Sclerosis (PLS) - This is rare. Only the upper motor neurones are affected so the clinical picture is characterised by spasticity of the arms and legs. Speech and swallowing may also be affected. progression may be very slow but many will develop lower motor neurone weakness within the first few years so they then move into the the category of ALS. In som cases, however, there may be a normal life span.
MND is a disease which usually affects older people becoming more common from the age of 60. The peak incidence is in the 70-80 years age group and the incidence declines thereafter.
Presentation
Motor neurone disease may present in a number of ways. Symptoms may be caused by upper or lower motor neurone degeneration. Depending on the area affected first, the symptoms will vary.
Signs of upper motor neurone damage
- weakness
- spasticity
- hyperreflexia
- spastic dysarthria
- difficulty with swallowing
Signs of lower motor neurone damage
- weakness
- fasciculations
- cramps
- hyporeflexia or absent reflexes
- hypo/hypernasal speech
- feeling breathless or difficulty with breathing
When making a diagnosis of MND a combination of upper and lower motor neurone signs should be present.
How the diagnosis is made . The diagnosis of motor neurone disease may be difficult to establish and a number of investigations may need to be performed. The diagnosis may be made by assessing the clinical signs and symptoms and observing the deterioration of these over time. A number of upper and lower motor neurone signs need to be detected before the diagnosis is definite.The El Escorial criteria were outlined at a consensus conference to assist in making a reliable diagnosis of MND for research purposes. Many people may be very likely to have MND but may not fulfil these strict criteria.