The exact cause of ALS is unknown, but about 10% of patients with ALS inherit the disease as an autosomal dominant trait. ALS may also be caused by a virus that creates metabolic disturbances in motor neurons or by immune complexes, such as those formed in autoimmune disorders. The leading theory is that the neurotransmitter glutamate contributes to cellular injury and neuronal degeneration.

Precipitating factors that can cause acute deterioration include severe stress, such as myocardial infarction, traumatic injury, viral infections, and physical exhaustion.

Common complications of ALS include respiratory tract infections such as pneumonia, respiratory failure, and aspiration; complications of physical immobility include pressure ulcers and contractures.

Signs and symptoms of ALS depend on the location of the affected motor neurons and the severity of the disease. Keep in mind that muscle weakness, atrophy, and fasciculations are the principal signs and symptoms of the disorder; that the disease may begin in any muscle group; and that, eventually, all muscle groups become involved. Unlike other degenerative disorders, such as Alzheimer’s disease, ALS doesn’t affect mental function.

The patient’s history may reveal other family members with ALS if the problem was inherited. In the early disease stages, the patient may report asymmetrical weakness first noticed in one limb. He also usually reports fatigue and easy cramping in the affected muscles. Inspection may reveal fasciculations in the affected muscles if these muscles aren’t concealed by adipose tissue and muscle atrophy. Fasciculations and atrophy are most obvious in the feet and hands.

As the disease progresses, the patient may report progressive weakness in muscles of the arms, legs, and trunk. Inspection reveals atrophy and fasciculations. Neurologic examination commonly reveals brisk and overactive stretch reflexes. Muscle strength tests confirm the reported muscle weakness.

When the disease progresses to involve the brain stem and the cranial nerves, the patient has difficulty talking, chewing, swallowing and, ultimately, breathing. In these patients, auscultation may reveal decreased breath sounds.

In some patients (about 25%), muscle weakness begins in the musculature supplied by the cranial nerves. When this occurs, initial patient history reveals difficulty talking, swallowing, and breathing. Occasionally, the patient may report choking. Inspection may reveal some shortness of breath and, occasionally, drooling.

Although no diagnostic tests are specific to this disease, the following tests may aid in its diagnosis: