Corpus callosum atrophy as a marker of clinically meaningful cognitive decline in secondary progressive multiple sclerosis.  Impact on employment status. 
Cognitive impairment in Multiple Sclerosis (MS) is more frequent and pronounced in secondary progressive MS (SPMS).  Cognitive decline is an important predictor of employment status in patients with MS.  Magnetic Resonance Imaging (MRI) markers have been used to associate tissue damage with cognitive dysfunction.  The aim of the study was to designate the MRI marker that predicts cognitive decline in SPMS and explore its effect on employment status.  30 SPMS patients and 30 healthy participants underwent neuropsychological assessment using the Trail Making Test (TMT) parts A and B, semantic and phonological verbal fluency task and a computerized cognitive screening battery (Central Nervous System Vital Signs).  Employment status was obtained as a quality of life measure.  Brain MRI was performed in all participants.  We measured total lesion volume, third ventricle width, thalamic and corpus callosum atrophy.  The frequency of cognitive decline for our SPMS patients was 80%.  SPMS patients differed significantly from controls in all neuropsychological measures.  Corpus callosum area was correlated with cognitive flexibility, processing speed, composite memory, executive functions, psychomotor speed, reaction time and phonological verbal fluency task.  Processing speed and composite memory were the most sensitive markers for predicting employment status.  Corpus callosum area was the most sensitive MRI marker for memory and processing speed.  Corpus callosum atrophy predicts a clinically meaningful cognitive decline, affecting employment status in our SPMS patients.