Which type of multiple sclerosis is characterized by a progressive course from the onset?

Primary Progressive Multiple Sclerosis (PPMS) is characterized by a steady progression of neurological function decline from the onset of symptoms without any distinct relapses or remissions. Individuals diagnosed with PPMS experience a gradual worsening of disability over time, which distinguishes it from other forms of multiple sclerosis.

In contrast to other types, such as Relapsing-Remitting Multiple Sclerosis (RRMS) where patients experience clear relapses followed by periods of remission, or Secondary Progressive Multiple Sclerosis (SPMS) which typically develops in someone who initially had RRMS, PPMS starts with a progressive trajectory right from the beginning. This makes it unique in its clinical presentation and management challenges, as patients do not experience the same episodic nature of symptoms that occurs in the relapsing forms of the disease.

Progressive-Relapsing Multiple Sclerosis (PRMS) also features a progressive course but includes occasional relapses, which further differentiates it from PPMS. Thus, by defining PPMS as having a continuous decline in function from the outset, it is clear why this type is the correct answer to the question.