Hemispheric Dissociation between Ipsilateral Motor and Contralateral Somatosensory Representation of the Paretic Hand: Deterioration of Hand Function after Hemispherotomy in a Case of Hemispheric Polymicrogyria

Aims: Hemispheric polymicrogyria (HPMG) often causes unilateral spastic cerebral palsy and severe therapy-resistant epilepsy. The most effective treatment regarding seizure freedom is hemispherotomy. Prediction of hand function after hemispherotomy is challenging, as PMG can not only harbor function, but also induce interhemispheric reorganization. Previous studies showed preserved postoperative grasp function when the paretic hand was controlled via ipsilateral corticospinal projections; whether such patients can show a deterioration of hand function is, however, not known.

Methods: We report a case of an 8-year-old girl with HPMG, therapy-resistant epilepsy, and good motor function of the paretic hand who underwent vertical parasagittal hemispherotomy.

Results: Preoperatively findings of the paretic hand were as follows:

• Good grasp function, some individual finger movements, and mirror movements.

• Assisting hand assessment: 66 units.

• Transcranial magnetic stimulation: lesional hemisphere: no response; contralesional hemisphere: bilateral short-latency responses.

• Functional MRI: bilateral central activation during active movement of the paretic hand; activation only in the HPMG during passive movement.

These findings suggested a “hemispheric dissociation” between an ipsilateral primary motor (M1) and a contralateral (i.e., in the HPMG) primary somatosensory (S1) representation of the paretic hand.

Postoperative findings were as follows:

• Clearly reduced function of the paretic hand.

• Steady improvement during intensive inpatient rehabilitation for 4 weeks with the AHA score already back to 49 units.

Conclusion: Like in a former study (Epilepsia, Zsoter et al 2012), in our patient with HPMG and hemispheric “M1-S1-dissociation” grasp function was preserved after hemispherotomy. Our novel finding here is that, with careful documentation of pre- and postoperative hand function, a clear deterioration of hand function after disconnection the S1-representation was seen, with rapid improvement during postoperative intensive rehabilitation. We speculate that the improvement reflects the habituation to the loss of somatosensory feedback.