Background: Relapsing-remitting multiple sclerosis (RRMS) is characterized by the occurrence of clinical relapses, followed by remitting phases of a neurological deficit. Clinical remission after a relapse can be complete, with a return to baseline function that was present before, but is sometimes only partial or absent. Remyelination and repair of the neuronal damage do contribute to recovery, but they are usually incomplete.
Objective: We tested the hypothesis that synaptic plasticity, namely long-term potentiation (LTP), may represent an additional substrate for compensating the clinical defect that results from the incomplete repair of neuronal damage.
Methods: We evaluated the correlation between a measure of LTP, named paired associative stimulation (PAS), at the time of relapse and symptom recovery, in a cohort of 22 newly-diagnosed MS patients.
Results: PAS-induced LTP was normal in patients with complete recovery, and reduced in patients showing incomplete or absent recovery, 12 weeks after the relapse onset. A multivariate regression model showed that PAS-induced LTP and age may contribute to predict null, partial or complete symptom recovery after a relapse.
Conclusion: Synaptic plasticity may contribute to symptom recovery after a relapse in MS; and PAS, measured during a relapse, may be used as a predictor of recovery.
Keywords: Evoked potentials; long term potentiation; paired associative stimulation; recovery; relapse; relapsing–remitting multiple sclerosis; remyelination; synaptic plasticity; transcranial magnetic stimulation.