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Amyotrophic lateral sclerosis

Also known as Lou Gehrig's disease (after the famous baseball player), ALS is the most common form of progressive motor neuron disease. The incidence is 1:100,000 prevalence 4-6:100,000. It appears mainly in advancing age and male slightly more than females.

In each of these diseases, the affected motor neurons undergo shrinkage, often with accumulation of the pigmented lipid (lipofuscin) that normally develops in these cells with advancing age. In ALS, the motor neuron cytoskeleton is typically affected early in the illness. Focal enlargements are frequent in proximal motor axons; ultrastructurally, these "spheroids" are composed of accumulations of neurofilaments.

Both upper and lower motor neuron abnormalities are found.

Clinical suspicion

Mixture of both upper and lower motor neuron abnormali?ties are found.

Typical patient with ALS develops progressive limb weakness affecting distal more than proximal areas, and especially affecting the small muscles of the hand. Early atrophy and fasciculations are prominent.

The deep tendon reflexes are usually preserved in the early phase of the disease, at least in the upper extremities. Signs of upper motor neuron involvement may develop at any time but almost always appear by the time muscle involvement has lasted a year. Characteristically bladder and bowel functions remain unaffected. ALS spares the extraocular muscles but in the late stages can interfere with supranuclear oculomotor control.

Amyotrophic lateral sclerosis may be associated with a form of late-life dementia characterized by prominent signs of frontal lobe dysfunction.

It progresses over 2 to 7 years until death.

Diagnosis

Mixture of LMND with exaggerated reflexes. Painless weakness and atrophy of the hands, fasciculations in the entire upper extremities, and spasticity and reflex hyperactivity of the legs with extensor plantar responses.

CSF is normal. Electrodiagnostic testing is helpful.

Prognosis

Average survival is 3yrs. Death from pulmonary insufficiency and infection are common.

N.B. Progressive bulbar palsy: a variant of ALS that causes relatively rapidly advancing upper and lower motor neuron involvement of the muscles of the jaw, pharynx, and tongue.

Treatment

There is no treatment capable of arresting the underlying pathologic process in ALS. The drug riluzole was approved for use in ALS because it produces a modest lengthening of survival. In one trial, the survival rate at 18 months with riluzole (100 mg/d) was similar to placebo at 15 months. The mechanism of this effect is not known with certainty; it may reduce excitotoxicity by diminishing glutamate release.

In the absence of a primary therapy for ALS, a variety of rehabilitative aids may substantially assist ALS patients.

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