Case report: Congenital mirror movements in a 12-year-old girl. Clinical and neurophysiological findings

Objectives: A 12-year-old girl of Arabic origin presented with isolated mirror-movements (MM) of the fingers. The neurological examination, EEG, cranial and spinal MRI and the patients history revealed normal findings.

Material and Methods: The patient performed fine motor skill tests, analysed with the ZEBRIS®-system, where tiny mobile loudspeakers are attached to both index fingers and thumbs in order to measure the distance between each fingers. Focal TMS delivered motor evoked potentials (MEP), active (AMT) and resting motor thresholds (RMT) and contralateral silent periods (CSP). Additionally we performed functional MRI (fMRI) and Magnetoencephalography (MEG).

Results: The detailed clinical examination, showed isolated MM of the fingers. We could not detect any MM during movement of hands or arms. The finger-tapping-tasks, evaluated with the ZEBRIS®-system revealed MM harmonizing exactly with the initiation of the movement in the task hand. The TMS-study delivered AMT=35% and RMT=38%. It was remarkable that even at low stimulus intensities ipsilateral MEPs (iMEP) were present, with the same latency as the contralateral MEP. We found normal values for the CSP latency and duration. In addition we found distinct Silent Periods (SP) in the ipsilateral muscle.

Conclusions: We saw a 12-year-old girl with congenital MM. Our data give strong evidence, that ipsilateral representations from the motor cortex to the finger muscles are established in our patient. We suggest that the SP of the ipsilateral muscle reflects the postexcitatory silent period following the iMEP. Our data replicate earlier findings in patients with MM showing ipsilateral corticospinal connections. In conclusion, investigation of patients with MM with focal TMS can provide new insights into the organisation and development of the corticospinal system. The additional results delivered by fMRI and MEG will be discussed after complete analysis.