Age at onset determines the occurrence of the progressive phase of multiple sclerosis.

We investigated the influence of age at disease onset on timing of the progressive phase in 957 patients with multiple sclerosis (MS). Age at onset powerfully predicts the probability of developing a primary progressive form of the disease. Moreover, age at onset strongly determines the time to conversion to secondary progression for patients presenting with a relapsing form. This suggests that age at onset strongly influences the neurodegenerative component of MS.