Increased intracortical facilitation in patients with autosomal dominant pure spastic paraplegia linked to chromosome 2p

There are at least seven clinically indistinguishable but genetically diffe rent types of autosomal dominant pure spastic paraplegia (ADPSP). In this s tudy we investigated electrophysiological characteristics in patients with ADPSP linked to chromosome 2p (SPG4). Twelve patients from six different fa milies with ADPSP linked to chromosome 2p and 15 control persons were inclu ded. Electromyography (EMG), motor and sensory nerve conduction, and motor evoked potentials using single and paired transcranial magnetic stimulation (PTMS) was performed. From the peripheral nervous system we found signs of motor and sensory axonal neuropathy. Motor evoked potentials disclosed gre atly reduced corticospinal tract conduction velocity and amplitude of evoke d potentials to the lower extremities indicating that the very marked spast icity predominantly seems to rely on dysfunction of the fast conducting axo ns of the pyramidal tract. PTMS showed an increased intracortical facilitat ion (ICF), which may reflect an impaired function of gamma -aminobutyric ac id (GABA)-controlled interneuronal circuits in the motor cortex, alternativ ely an increased glutamatergic transmission or a compensatory recruitment o f a larger number of neurones with corticospinal projections.