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What's the difference between MND and ALS?


This article explains why Motor Neuron Disease is often called Amyotrophic Lateral Sclerosis, and other terms that Neurologists use.

The term Motor Neuron Disease (MND) encompasses several different conditions whose common feature is the premature degeneration of motor nerves (known as neurons or sometimes neurones). There are two groups of motor neurons - upper motor neurons travelling from the brain down the spinal cord, and lower motor neurons branching outwards to supply muscles in the face, throat, arms, chest and legs. Both groups of neurons tend to be involved in MND but to varying extents, which is one of the many reasons why each patient's disease is subtly unique.

Nearly 90% of patients with MND have the mixed ALS form of the disease, so that the terms MND and ALS are commonly used to mean the same thing. Within this large ALS group there is still a huge variation in the way the disease presents and progresses. With further study it is apparent that the other 10% of patients tend to show either predominantly lower motor neuron damage with prominent muscle wasting, or solely upper motor neuron degeneration with relatively little muscle wasting but prominent stiffness. The former group is termed Progressive Muscular Atrophy (PMA) and the latter group Primary Lateral Sclerosis (PLS), to reflect each end of a spectrum. Some of these cases, particularly those with PLS, seem to have a much slower rate of progression.

So the terms MND and ALS effectively mean the same thing. Finally, there are other ways that neurologists sometimes categorise MND cases. One method is by the site where the disease symptoms being - for example if it is in the speech and swallowing motor nerves (which arise from the 'bulb' of the brain stem) then it is termed bulbar-onset MND. Another group of MND patients have a disease that predominantly affects the arm muscles, and is termed the 'flail arm' variant. These so-called 'regional phenotypes' follow some common trends in their patterns of progression, but no system of categorisation to date can predict with certainty the course of the disease for an individual patient.

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