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Brain volumes in children with multiple sclerosis (MS) were smaller than in those without the disease due to a lack of age-expected brain growth and progressive atrophy, researchers reported.

Using longitudinal MRI data from patients with relapsing-remitting MS onset prior to age 18, Berengere Aubert-Broche, PhD, of McGill University in Montreal and colleagues noted that "significant group and age interactions were found with the adjusted models fitting brain volumes and normalized thalamus volumes (P<0.10-4)." They also found that T2 lesion volume correlated with a greater reduction in age-expected thalamic volume compared with children without MS......... Read More - http://www.ms-uk.org/paediatric

Of course, this is the vascular comorbidity, the angiopathy caused by the virus VZV.
Gates are jammed, cellular respiration is impaired, cells loose size.
Atrophy of any tissue means a decrement in the size of the cell http://en.wikipedia.org/wiki/Cerebral_atrophy