Interferon beta treatment for multiple sclerosis has a graduated effect onMRI enhancing lesions according to their size and pathology

Objective-The ability of recombinant human interferon beta-1a (rh-IFN beta- 1a) to suppress multiple sclerosis activity, evaluated from MRI, was assess ed across a range of lesions enhancing at different gadolinium-DTPA (Gd) do ses and with different sizes. Methods-Every 4 weeks, standard dose (Sd; 0.1 mmol/kg Gd) and triple dose ( Td; 0.3 mmol/kgGd) MRI were obtained from 18 patients with relapsing-remitt ing multiple sclerosis for 3 months before and 4 months after starting trea tment with 44 mu g rh-IFN beta-1a subcutaneously, once a week. Results-The total numbers of enhancing lesions were 145 and 126 on Sd scans and 278 and 192 on the Td scans obtained before and after treatment. The i ntroduction of treatment decreased, on average, the rate of appearance of n ew enhancing lesions seen on Sd and Td scans by 37% (p<0.001). Treatment ef fects on new enhancing lesions seen on Td scans was, on average, 28% higher than on those seen on Sd scans. The distribution of lesion sizes on Td sca ns changed significantly during the treatment period (p=0.05), due to a mar ked decrease in the number of small lesions. Conclusions-The effect of 44 mu g rh-IFN beta-1a in reducing multiple scler osis disease activity, as monitored by Gd enhanced MRI, is not homogeneous, but graduated according to the pathological characteristics and size of th e lesions.