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The motor neuron diseases 

The motor neuron diseases

Chapter:
The motor neuron diseases
Author(s):

Alice Brockington

and Pamela J. Shaw

DOI:
10.1093/med/9780199204854.003.02415_update_001

Update:

This chapter has been extensively updated, most notably the sections on classification of the motor neuron diseases, amyotrophic lateral sclerosis, and spinal muscular atrophies.

Updated on 28 Nov 2012. The previous version of this content can be found here.
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date: 28 March 2017

Motor neuron diseases are a family of conditions that lead to selective loss of function of the lower and/or upper motor neurons controlling the voluntary muscles of the limbs or bulbar region. Precise diagnosis is essential for prognosis, identification of those diseases with genetic implications, and for (in a very few cases) specific treatment.

Amyotrophic lateral sclerosis (ALS) is the most common of the motor neuron diseases—a diffuse neurodegenerative disorder of (usually) unknown cause, with the brunt of pathology borne by both upper and lower motor neurons. It causes progressive paralysis of the muscles of the bulbar region (affecting speech and swallowing), limbs, and respiratory muscles. Upper and lower motor neuron signs in all three body regions are required for a definite diagnosis (El Escorial criteria). There is no specific curative treatment: the disease progresses relentlessly, with few patients surviving beyond 5 years from diagnosis.

A number of rarer motor neuron diseases affect exclusively either lower or upper motor neurons. These include childhood spinal muscular atrophy, Kennedy’s disease (X-linked recessive bulbospinal neuronopathy), monomelic motor neuronopathies, and multifocal motor neuropathy with conduction block, which may improve with high-dose intravenous human immunoglobulin therapy. Upper motor neuron syndromes are the rarest forms of motor neuron disease and include primary lateral sclerosis, hereditary spastic paraplegia, and the dietary spastic parapareses—lathyrism and konzo.

Accurate diagnosis depends on determination of upper and/or lower motor neuron involvement by clinical and electrophysiological examination, the age of onset, the rate of deterioration; and whether there is familial occurrence. Precise diagnosis is essential for prognosis, identification of those diseases with genetic implications, and (in a very few cases) for specific treatment. Motor neuron diseases are incurable for the most part, hence treatment must aim to overcome, or minimize, the diverse disabilities.

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