Types of ALS
An estimated 90% or more of all ALS cases are considered sporadic, which means there is no known cause or family history of ALS. Up to 10% of all ALS cases are familial, which means a child inherits ALS from a parent.

​Beyond these two categories, there are subtypes, or forms, of ALS that begin by affecting different parts of the body.

Primary Lateral Sclerosis

Primary lateral sclerosis (PLS) is a rare motor neuron disease that only affects the upper motor neurons. PLS tends to progress more slowly than ALS, has a longer life expectancy, and isn’t considered fatal.

​Because the initial symptoms of PLS and ALS can be similar, it may take a few years before a neurologist can verify whether a patient has PLS or slow-progressing ALS. Sometimes an initial PLS diagnosis changes to ALS when lower motor neuron involvement becomes apparent.

Progression of PLS varies from person to person. Symptoms can include leg and arm weakness, muscle stiffness, problems with balance, and difficulty speaking and swallowing.

Progressive Muscular Atrophy

Progressive muscular atrophy (PMA) is a rare motor neuron disease that affects the lower motor neurons and has similarities to ALS. A PMA diagnosis can change to an ALS diagnosis if additional symptoms develop. ​

Pseudobulbar Palsy

This condition starts by affecting the upper motor neurons that control speaking, swallowing, and chewing. It is also associated with sudden episodes of involuntary laughing or crying. People with pseudobulbar palsy often go on to develop ALS. ​

What are motor neurons?

Motor neurons are nerve cells in the brain that send messages to voluntary muscles throughout the body. When ALS causes motor neurons to deteriorate, the messages are disrupted, which leads to muscle weakness, atrophy, and ultimately paralysis.

Upper motor neurons are located in the upper prefrontal cortex of the brain and affect behavior and executive function. Lower motor neurons are located in the brainstem and spinal cord and are connected to muscles in the limbs and face and neck region. 

In traditional ALS, both the upper and lower motor neurons are affected. In PMA, just the lower motor neurons are affected. In PLS, just the upper motor neurons are affected.