What type of Multiple Sclerosis is defined by a steady decline in function from onset?

Primary Progressive Multiple Sclerosis is characterized by a gradual and continuous decline in neurological function from the onset of symptoms, without the distinct bursts of relapses and remissions that are seen in other forms of the disease. This type of MS affects individuals differently, but the defining feature is the ongoing progression of disability rather than fluctuations in well-being.

In Primary Progressive MS, there are no periods of recovery or stable function as seen in Relapsing-Remitting MS, where the individual experiences attacks followed by partial or complete recovery. Additionally, Secondary Progressive MS evolves from Relapsing-Remitting MS and may initially have relapses, but eventually progresses to a steady decline. Progressive-Relapsing MS also features a progressive course but includes occasional relapses, signifying that Primary Progressive MS is unique in its relentless, uninterrupted progression from the time of onset without these intervening phases.