Short-latency afferent inhibition predicts verbal memory performance in patients with multiple sclerosis

The pathogenesis of cognitive deficits in multiple sclerosis (MS) patients is the subject of debate. A causative role of grey matter impairment has been suggested. Acetylcholinesterase inhibitors have been proposed in the treatment of cognitive impairment in MS. Short-latency afferent inhibition (SAI) is a cortical phenomenon assessed by a transcranial magnetic stimulation protocol that provides an in vivo index of central cholinergic function.

We recruited 20 consecutive relapsing-remitting or secondary progressive MS patients showing normal upper limb somatosensory and motor evoked potentials. SAI of the left-hand motor cortex from median nerve stimuli was tested. A matched group of 20 healthy subjects was also assessed. All patients underwent neuropsychological assessment with Rao's Brief Repeatable Battery (BRB). Multiple regression was performed on the number of failed tests and on scores of single BRB tests as dependent variables with Extended Disability Status Scale (EDSS) score, SAI, age, gender and disease duration as regressors. Patients with impaired SAI, were reassessed after a single oral dose of rivastigmine.

SAI was a significant predictor of the score in tests that assess verbal memory. EDSS score and age were found as predictors of the other BRB tests. SAI was significantly improved by oral rivastigmine.

Our data confirm that cognitive impairment in MS is multifactorial. The performances in the subdomain of verbal memory are predicted by SAI. These results favour the hypothesis of grey matter involvement and suggest a role of acetylcholine dysfunction in the pathogenesis of some aspects of cognitive deficits in MS.