Different types of MND
Yes, there are different types of motor neurone disease. Doctors and patients often use the term motor neurone disease as an umbrella term to describe the condition rather than the actual sub-type of motor neurone disease, which can make things confusing. Additionally, there can be an overlap between the various subtypes.
Amyotrophic lateral sclerosis (ALS):
ALS is the most common form of MND and accounts for about 60 -70% of the total MND cases. Men are more commonly affected than women. In this type of MND, both the upper motor neurones and lower motor neurones degenerate at the same time. Symptoms and signs depend upon the area of the body where the muscles are affected first (e.g. arm or leg) and can include muscle wasting, weakness, stiffness, cramps and rippling of the muscles, known as fasciculations. Over time, as ALS progresses, different areas of the body become involved. Involvement of the muscles controlling speech, swallowing and breathing can also occur.
Progressive muscular atrophy
Progressive muscular atrophy accounts for perhaps 10% of cases of MND. In this type of MND, only the lower motor neurones degenerate and life expectancy is longer than that in ALS. Sometimes MND can initially present as progressive muscular atrophy but over time the upper motor neurons can be involved and the diagnosis then changes to ALS. Men are more likely to be affected than women.
Primary lateral sclerosis
This is an uncommon form of MND accounting for approximately 1-2% of cases. In this type of MND, only the upper motor neurones degenerate. Sometimes MND can initially look like primary lateral sclerosis but over time the lower motor neurones can become involved and the diagnosis changes to ALS. After 5 years it is rare for PLS to convert to ALS, however this may still occur.
In true cases of primary lateral sclerosis the condition progresses slowly and life span may not be reduced although disability levels can be high. Common symptoms and signs include muscle weakness, stiffness and increased reflexes response.
Progressive bulbar palsy
About 20% of all cases of MND can present as progressive bulbar palsy. The term "bulbar" refers to an area at the base of the brainstem, called the medulla oblongata. Progressive bulbar palsy is a type of MND that involves degeneration of upper and lower motor neurones from that area. These motor neurones are responsible for innervating the muscles of the tongue, pharynx and larynx (called the bulbar muscles) and so the symptoms of progressive bulbar palsy include wasting, weakness or stiffness of the tongue, difficulty with speaking and swallowing and problems with the thickness or amount of saliva
Progressive bulbar palsy is a term reserved for involvement only of the bulbar muscles in MND. Some people can develop problems with the bulbar muscles first and then go on to develop problems in the arms or legs – this is a form of ALS rather than progressive bulbar palsy. Likewise, the majority of people with ALS develop involvement of the bulbar muscles at some stage during the condition.
Flail arm / Flail leg variants
About 5-10% of all cases of MND can present with predominant lower motor weakness in both arms (Flail arm / man in a barrel syndrome) or in both legs (Flail leg). This is slowly progressive.