Symptoms usually do not develop until until after age 50. Progressive loss of muscle strength and coordination eventually interfere with the ability to perform routine activities, such as going up steps, getting out of a chair, or swallowing. Occasionally, breathing or swallowing muscles may be the first to be affected.

As the disease progresses, more muscle groups are affected and patients become progressively incapacitated. There is no effect on the ability to think or reason.

Symptoms include:

• muscle weakness, decrease in muscle strength and coordination
  • gradual onset
  • progressively worsens
  • commonly involves one limb initially (such as the hand)
  • progresses to difficulty lifting, climbing stairs and walking
• paralysis
• muscle cramps
• voice changes, hoarseness
• speech impairment, slow or abnormal speech pattern
• difficulty swallowing, gags or chokes easily
• difficulty breathing (increasing effort required to breathe)
• head drop due to weak spinal and neck muscles

• muscle contractions
• muscle spasms
• muscle atrophy
• ankle, feet and leg swelling
• weight loss
• drooling

A neuromuscular examination indicates weakness, often beginning in one limb or in proximal groups (such as shoulders or hips). There may be muscle tremors, spasms, twitching, or muscle atrophy (loss of tissue). Atrophy and twitching of the tongue are common.

The gait may be stiff or clumsy. Reflexes may be abnormal, including loss of the gag reflex. Some patients have "emotional incontinence" in which it is hard to control crying or laughing.

• An EMG indicates that the motor nerves are not functioning, yet the sensory nerves are normal.
• A Head CT or MRI of head may be done to rule out other conditions.
• If there is a family history, a genetic test may be performed.
• A breathing test may be given to see if respiratory muscles are affected.
• Blood tests can exclude other conditions that may cause similar symptoms.