Progressive muscular atrophy (PMA), also known as
Duchenne-Aran muscular atrophy and
Duchenne-Aran disease — is a rare subtype of
motor neuron disease (MND) that affects only the
lower motor neurones. PMA is thought to account for around 4% of all MND cases. This is in contrast to
amyotrophic lateral sclerosis (ALS), the most common form of MND, which affects both the
upper and
lower motor neurones, or
primary lateral sclerosis, another rare MND variant, which affects only the upper motor neurons. The distinction is important because PMA is associated with a better prognosis than classic ALS.