Impairment of transcallosal inhibition in patients with corticobasal degeneration

Objective: To evaluate the motor function of the transcallosal pathways in patients with clinical diagnosis of corticobasal degeneration (CBD). Methods: In a group of 7 patients (4 males, 3 females; mean age 70.6 years) with clinical diagnosis of probable CBD (and in 8 age-matched normal controls) we evaluated the suppression of the ongoing voluntary EMG activity in the opponens pollicis muscle induced by focal transcranial magnetic stimulation (TMS) of the ipsilateral hand motor cortex. Such ipsilateral silent period (iSP) is mediated from one motor cortex to the contralateral side via a transcallosal pathway. In addition, CBD patients were investigated with magnetic resonance imaging (MRI) and neuropsychological assessment. Results: iSP was normal in 4 CBD patients, while it was bilaterally disrupted in the other 3. MRI showed an atrophy of the corpus callosum (middle-posterior part of the trunk) in the CBD patients with iSP disruption. Neuropsychological evaluation showed in patients with iSP impairment a decrease of verbal fluencies associated with an impairment of attentive function. Conclusions: A proportion of CBD patients shows physiological evidence of impaired callosal motor function and atrophy of the corpus callosum on MRI, possibly correlated to dysphasic and cognitive disorders.