['We performed diffusion tensor imaging (DTI) and magnetic resonance spectroscopy (MRS) studies in a group of patients with subacute sclerosing panencephalitis (SSPE) in order to estimate the pathologic process underlying the phenotypic variability.', 'Patients with SSPE who had MRI including DTI and MRS examinations were evaluated according to their clinical status as determined by the SSPE Scoring System and their mental age as determined by tests appropriate for age and developmental level. Comparisons of fractional anisotropy (FA) and apparent diffusion coefficient (ADC) values and metabolite ratios of frontal periventricular white matter, parieto-occipital periventricular white matter, and globus pallidus in both hemispheres were made between control and SSPE groups, and between SSPE subgroups.', 'Control (n = 18) and SSPE (n = 39) groups differed in all DTI and MRS parameters except FA, choline (Cho), and Cho/creatine (Cr). SSPE cases had higher ADC and lower N-acetylaspartate (NAA), NAA/Cho, and NAA/Cr in all regions of interest, suggesting cell loss. Disease progression rate and neurologic deficit appeared to be associated with the degree of ADC elevation and NAA reduction: the group with severe global deterioration had the lowest NAA (230.75 ± 197.97 in forceps minor), and rapid progression was associated with acute reduction in NAA.'] Is neuronal loss an early component of subacute sclerosing panencephalitis?