A motor neuron disease
) is any of several neurological disorder
s that selectively affect motor neuron
s, the cells that control voluntary muscles
of the body. They include amyotrophic lateral sclerosis
(ALS), hereditary spastic paraplegia
(HSP), primary lateral sclerosis
(PLS), progressive muscular atrophy
(PMA), progressive bulbar palsy
(PBP) and pseudobulbar palsy
. Spinal muscular atrophies
(SMA) are sometimes included in the group by some neurologists but it is different disease with clear genetic cause. They are neurodegenerative
in nature and cause increasing disability and eventually, death.
In the United States, the term is often used to denote ALS, the most common disorder in the group. In the United Kingdom, the term is also spelt motor neurone disease
(MND) and is sometimes used for the entire group; but mostly it refers to ALS.
While MND refers to a specific subset of similar diseases, there are numerous other diseases of motor neuron
s that are referred to collectively as "motor neuron disorders", for instance disease belonging to spinal muscular atrophies
. However, they are not classified as "motor neuron diseases" by the tenth International Statistical Classification of Diseases and Related Health Problems
(ICD-10), which is the definition followed in this article.
Motor neuron diseases affect either upper motor neuron
s (UMN) or lower motor neuron
s (LMN), or both: