The symptoms of ALS appear gradually.

So gradually, in fact, many patients may miss the earliest signs

The first symptoms patients tend to notice include:

• Twitching
• Cramping
• Stiffness in muscles
• Muscle weakness affecting an arm or leg
• Slurred or nasal speech
• Difficulty chewing or swallowing

Muscles damaged early on by the disease are often the parts of the body that show symptoms first. Symptoms may be subtle—patients may notice that they are tripping more often when they walk, or that they are having trouble buttoning their shirt. Overall, muscle weakness is the predominant initial symptom, occurring in about 60% of patients.

As the disease progresses, additional parts of the body become damaged as the muscle weakness and atrophy spreads. For a patient to be diagnosed with ALS, they must present with symptoms in of both upper and lower neuron damage that cannot be attributed to any other condition.

Typically, ALS does not affect cognitive abilities. However, evidence exists that a small percentage of patients may, in fact, experience difficulties with their memory and decision-making abilities, even developing some form of dementia. It's important that patients make informed decisions about their health care in advance, in case there is any diminishment in cognitive abilities.

In the later stages of ALS, the muscles of the respiratory system become increasingly weak, eventually requiring mechanical assistance to help with breathing.