To assess if clinical relapses and radiological disease activity correlates with neurological disability in primary progressive multiple sclerosis (PPMS), and to determine if there is any correlation between lesional load, cortical atrophy and time to disability. Furthermore, to expand PPMS natural history knowledge.

PPMS has a distinct clinical phenotype representing10-15% of MS cases, characterized by disease progression from onset, leading to cumulative disability; although acute clinical or radiological relapses may occur.

Actually, there is lack of evidence to support that disease activity clearly impacts in PPMS prognosis and data from Latin American is scarce.

Patients with PPMS diagnosed from January/2007 to October/2018 in a referral tertiary center in Buenos Aires, Argentina, were included. Demographic and clinical features were analyzed. Brain and spinal cord MRI were evaluated.

Volumetric lesion load and cortical atrophy were determined by automated software. Disease activity was defined by clinical relapses or imaging(gadolinium-enhancing lesions, new or unequivocally enlarging T2-lesions) 

Were included 105 patients (M:F=1:1.6, median age at diagnosis 48 (18-75 range). Most frequent initial symptom was myelitis 70%. Oligoclonal bands were positive (type II or III) in 84% of patients.

17% of patients presented clinical relapses and 48% had radiological activity. Median times to EDSS 4, 6 and 8 were 71 (0-444), 84 (9-408), and 114 (36-300) months respectively.

This is the first specific PPMS case series from Latin America, which support that clinical and radiological phenotype is similar than those previously published from North America and Western Europe, and brings contribution to PPMS knowledge.

Even being a small cohort; we did not found significant differences in our primary outcomes.