The course of multiple sclerosis is largely unpredictable, and there are different types of MS that someone can be diagnosed with.
Some people are minimally affected by the disease while in others the impact of the disease is more severe, resulting in swift progress towards disability. Although every person will experience a different combination of symptoms, there are a number of distinct patterns relating to the course of the disease.
Relapsing-remitting multiple sclerosis (RRMS)
RRMS is the most common disease course characterised by clearly defined attacks or increased neurological activity followed by periods of complete or partial recovery. During periods of remission, all symptoms might disappear, however some might continue or become permanent. There is however no apparent ongoing accumulation of disability. Approximately 85% of people with MS are initially diagnosed with RRMS.
Secondary progressive multiple sclerosis (SPMS)
SPMS is diagnosed when the condition follows a history of worsening
after an original diagnosis of RRMS. To date, there is no clinical test
to provide a transition point showing when RRMS changes to SPMS.
In the past, in the absence of treatment, transition to SPMS took about
10 years. 90% of people with RRMS developed SPMS within 20-25 years
after diagnosis. With the newer Disease Modifying Therapies available,
these figures are changing. SPMS can be further characterised at
different points in time as either active (with relapses and/or evidence
of new MRI activity) or non-active, as well as with progression
(evidence of disease worsening on an objective measure of change over
time, with or without relapses) or without progression.
Primary progressive multiple sclerosis (PPMS)
PPMS is diagnosed when the condition follows a progressive course
from onset, characterised by a worsening of neurological function
(accumulation of disability) in the absence of exacerbations prior to
clinical progression. PPMS can have brief periods when the disease is
stable, with or without a relapse or new MRI activity, as well as
periods when increasing disability occurs with or without new relapses
or lesions on MRI. PPMS can be further characterised at different
points in time as either active (with an occasional relapse and/or
evidence of new MRI activity) or non-active, as well as with progression
(evidence of disease worsening on an objective measure of change over
time, with or without relapse or new MRI activity) or without
progression.
PPMS involves much less inflammation of the type seen in relapsing
MS. As a result, people with PPMS tend to have fewer brain lesions than
people with RRMS and more lesions in the spinal cord than in the brain,
making PPMS more difficult to diagnose and treat than the relapsing form
of MS.