Stephen Hawking has lived with ALS for the majority of his life. He's pictured delivering a lecture to mark NASA's 50th anniversary in 2008.

Paul. E. Alers/NASA via Getty Images

ALS Symptoms and Diagnosis

When ALS begins, its symptoms are often hard to notice. Some people may become clumsier than usual. Others may experience muscle weakness or stiffness. Still others may slur their words.

Which symptoms appear first depends on the muscles affected. When the disease damages lower motor neurons, muscles in a particular part of the body (like the hand or foot) will be affected. When ALS impacts upper motor neurons, people will experience general clumsiness, slurred speech and difficulty swallowing. Eventually, the disease will spread to all of the body's muscles and lead to total paralysis.

In the early stages of the disease, symptoms may include muscle weakness in one part of the body (an arm or leg); clumsiness, such as tripping and dropping things; difficulty speaking or swallowing; muscle twitches (fasciculations) and cramps; fatigue in the arms or legs; weight loss and the loss of muscle mass; and uncontrolled laughing or crying, called emotional incontinence.

How the disease progresses varies from person to person. But as it worsens, people may experience shortness of breath or difficulty breathing, stiff muscles and exaggerated reflexes (including a strong gag reflex).

Eventually people may lose the ability to breathe on their own and will need to be put on a ventilator. Most people with the disease eventually die from respiratory failure or pneumonia -- because they can't swallow properly, they aspirate food and fluid into the lungs.

While ALS can devastate the body, it doesn't affect involuntary muscles (such as bowel and bladder function), the senses (smell, taste, hearing and sight), or the ability to think.

ALS isn't an easy disease to diagnose. Its symptoms mimic those of other diseases (such as Parkinson's) and there isn't one test to spot it. Often doctors will rule out other diseases to arrive at a diagnosis. For the very small percentage of people with familial ALS, there's a genetic test to look for the faulty SOD1 gene. However, because most people with ALS don't have this gene, the test isn't very useful.

Some tests that are used to diagnose ALS include:

  • Electromyogram (EMG) inserts a thin electrode into the muscle to detect electrical activity and see how well the muscles are working.
  • Nerve conduction velocity (NCV) passes a small shock through a nerve to measure the speed of nerve signals.
  • Spinal tap inserts a needle into the spinal canal and removes fluid (cerebrospinal fluid) for testing.
  • X-rays, CT scans and MRI create images of the brain and spinal cord to look for any abnormalities.
  • Blood and urine tests look for abnormal levels of certain substances in the blood and urine.
  • Muscle or nerve biopsy removes a small sample of tissue, which is sent to a lab for testing.

Once a person is diagnosed, the average survival time is only three to five years. However, about 10 percent of people with ALS live for 10 years or more, and the lifespan for ALS patients is increasing as new treatments are introduced [source: ­ALSA].