SHORT REPORT ABSTRACT: The role of intracortical organization in the pathophysiology of cerebral palsy (CP) is not clear. We used transcranial magnetic stimula- tion to investigate the paradigm of transcallosal inhibition (TI) in a group of adolescent patients with diplegic CP (n = 4), hereditary spastic paraplegia (n = 2), and healthy control adolescents (n = 4). None of the patients with CP showed TI, whereas all other subjects had normal TI. These findings indicate a lack of inhibitory control of the motor cortex in CP. © 1999 John Wiley & Sons, Inc. Muscle Nerve 22: 255–257, 1999 ABSENCE OF TRANSCALLOSAL INHIBITION IN ADOLESCENTS WITH DIPLEGIC CEREBRAL PALSY FLORIAN HEINEN, MD, 1 JANBERND KIRSCHNER, MD, 1 URBAN FIETZEK, 1 FRANZ-XAVER GLOCKER, MD, 2 VOLKER MALL, MD, 1 and RUDOLF KORINTHENBERG, MD 1 1 Department of Neuropediatrics, Albert-Ludwigs-Universita ¨t Freiburg, Freiburg, Germany 2 Department of Neurology, Albert-Ludwigs-Universita ¨t Freiburg, Freiburg, Germany Accepted 14 August 1998 Cerebral palsy (CP) is an umbrella term for a group of frequent disorders of motor function due to a nonprogressive lesion of the developing brain. In most patients one predominant motor manifestation is spasticity. This is thought to be caused mainly by hyperexcitability of the spinal alpha motoneuron, which in turn has been attributed to interruption of descending modulatory influences and impaired lo- cal spinal regulation. In addition, altered muscle fi- ber properties may play an important role in the development of muscle hypertonia. 1 So far however, the role of intracortical control in the pathophysiol- ogy of spasticity remains speculative. In an attempt to establish whether intracortical organization is impaired in cerebral palsy, we used transcranial magnetic brain stimulation to investi- gate the paradigm of transcallosal inhibition (TI). TI is due to activation of callosal fibers, which connect both primary motor cortices. It results in a suppres- sion of ongoing voluntary electromyographic activity in the ipsilateral distal hand muscles after focal mag- netic stimulation. 3–5 This inhibitory phenomenon is probably fully developed around the age of 10 years. 3,6 MATERIALS AND METHODS A group of adolescent patients with diplegic cerebral palsy (n = 4, age 12–15 years) or hereditary spastic paraplegia (n = 2, age 15 and 16 years) and healthy control adolescents (n = 4, age 10–15 years) were studied with local ethical committee approval and informed consent. Table 1 shows the clinical find- ings in the upper limbs of each subject and, where available the results of cerebral magnetic resonance (MR) scans. Focal transcranial magnetic stimulation (TMS) was performed over the hand area of the left motor cortex with a figure-of-eight magnetic coil, using a MagStim 200 magnetic stimulator. Compound muscle action potentials (CMAPs) were recorded from both first dorsal interosseous (FDI) muscles using surface electrodes and a Nicolet Viking IV elec- tromyograph apparatus. The precise site of the coil was adjusted to produce a maximal response in the right FDI. After determining motor threshold and central conduction time (CCT), another eight stimuli were Abbreviations: CCT, central conduction time; CMAP, compound muscle action potential; CP, cerebral palsy; FDI, first dorsal interosseous; MR, magnetic resonance; PSP, postexcitatory silent period; PVL, periventricu- lar leucomalacia; TI, transcallosal inhibition; TMS, transcranial magnetic stimulation Key words: cerebral palsy; transcranial magnetic stimulation; transcallo- sal inhibition; children Correspondence to: Florian Heinen, Children’s Hospital, Freiburg Univer- sity, Department of Neuropediatrics, Mathildenstrasse 1, D-79106 Freiburg, Germany CCC 0148-639X/99/020255-03 © 1999 John Wiley & Sons, Inc. Short Reports MUSCLE & NERVE February 1999 255