Clinical course of critical demyelinating lesion-associated progressive multiple sclerosis

Progressive multiple sclerosis (MS) is usually associated with progressive asymmetrical motor impairment. A single critical demyelinating lesion anatomically associated with motor impairment was seen in > 20% of patients with progressive MS. The assessment of critical lesion-associated progressive MS requires understanding their clinical course, how prior inflammatory relapse location and their first MRI appearance relates to progressive motor impairment.

To determine: (1) clinical course and prior relapse location and (2) interval between first MRI critical lesion evidence and progressive motor impairment in patients with progressive MS with a single critical lesion.

Prospective, consecutively accrued patients with progressive MS were seen at a tertiary MS clinic (July 1, 2021-June 30, 2022). Patients with one critical lesion anatomically associated with progressive motor impairment were included. Patients with two or more tandem critical lesions along the same corticospinal tract or too extensive demyelinating lesion burden to determine the association between motor impairment and one critical lesion were excluded. A location-related relapse (LRR) was defined as a prior acute inflammatory demyelinating event at the same CNS site subsequently identified with critical lesion-associated motor progression. Clinical course was progressive from onset [primary progressive MS (PPMS)] or relapse-onset [secondary progressive MS (SPMS)] with SPMS dichotomized to those with or without LRR. MRIs were reviewed determining the earliest MRI critical lesion appearance and duration between this and the onset of progressive motor impairment.

53 of 266 (20%) patients with progressive MS had a single critical lesion associated with motor progression. Clinical course was SPMS in 36/53 (68%) and PPMS in 17/53 (32%). SPMS critical lesion onset was LRR-associated in 26/36 (72%). Critical lesion was first MRI-evident a median of 2.2 years before the onset of motor progression in SPMS (IQR -1.7 to 4.6) and -4.5 years (IQR -10.6 to -2.5) in PPMS with negative values indicating first MRI evidence came after motor progression onset.

In people with a single critical lesion-associated motor progression, this typically presents as SPMS and often follows an LRR. This emphasizes the anatomic association between initial lesion-associated inflammatory presentation and subsequent motor progression.