Motor neurone disease

Motor neuron diseases (MNDs) are a group of neurodegenerative disorders that selectively affect motor neurons, the cells which control voluntary muscles of the body. According to ICD-11, the following disorders are counted among motor neuron diseases: amyotrophic lateral sclerosis (ALS), progressive bulbar palsy (PBP), pseudobulbar palsy, progressive muscular atrophy (PMA), primary lateral sclerosis (PLS), and monomelic amyotrophy (MMA), as well as some rarer variants resembling ALS. Motor neuron diseases affect both children and adults. While each motor neuron disease affects patients differently, they all cause movement-related symptoms, mainly muscle weakness. Most of these diseases seem to occur randomly without known causes, but some forms are inherited. Studies into these inherited forms have led to discoveries of various genes (e.g. SOD1) that are thought be important in understanding how the disease occurs. Symptoms of motor neuron diseases can be first seen at birth or can come on slowly later in life. Most of these diseases worsen over time; while some of them shorten one's life expectancy (e.g. ALS), others do not. Currently, there are no approved treatments for the majority of motor neuron disorders, and care is mostly symptomatic. In the United States, the term motor neuron disease is often used to denote amyotrophic lateral sclerosis (Lou Gehrig's disease), the most common disorder in the group. In the United Kingdom, the term is spelled motor neurone disease and is frequently used for the entire group, but can also refer specifically to ALS. While MND refers to a specific subset of similar diseases, there are numerous other diseases of motor neurons that are referred to collectively as 'motor neuron disorders', for instance the diseases belonging to the spinal muscular atrophies group. However, they are not classified as 'motor neuron diseases' by the 11th edition of the International Statistical Classification of Diseases and Related Health Problems (ICD-11), which is the definition followed in this article. Motor neuron disease describes a collection of clinical disorders, characterized by progressive muscle weakness and the degeneration of the motor neuron on electrophysiological testing. As discussed above, the term 'motor neuron disease' has varying meanings in different countries. Similarly, the literature inconsistently classifies which degenerative motor neuron disorders can be included under the umbrella term 'motor neuron disease'. The four main types of MND are marked (*) in the table below.