Seventeen patients with relapsing remitting multiple sclerosis (MS) Previous work using positron emission tomography (PET) has demonstrated a generalised coupled reduction in both cerebral oxygen utilisation and blood flow in MS patients. The reduction was found in both white and grey matter and correlated with cognitive impairment, rather than with locomotor disability or clinical disease duration.'9 Recently, single photon emission computed tomography (SPECT) has given information similar to that provided by PET in the study of cognitive deficit associated with Alzheimer's dementia.2"22The aim of this study was to examine the regional distribution of 99mTc HMPAO in the brain, the extent of cerebral lesions by MRI and their