Axonal integrity of corticospinal projections to the upper limbs in patients with pure hereditary spastic paraplegia.

OBJECTIVE

Patients with hereditary spastic paraplegia (HSP) show pathological findings when transcranial magnetic stimulation (TMS) is used to test corticospinal projections to the lower limbs. However, TMS studies on the pathways to the upper limbs revealed inconsistent results. Standard clinical TMS procedures are not well suited for testing axonal integrity, which is thought to be affected in HSP. More appropriate measures can be achieved by testing corticospinal projections with the triple stimulation technique (TST).

METHODS

TST was used to test axonal integrity of corticospinal projections to the upper limbs in 15 patients with pure HSP (13 of whom were tested positive for SPG 4) and 15 healthy control subjects.

RESULTS

TST measurements revealed normal values for corticospinal transmission in all 15 patients with pure HSP, as well as in all healthy control subjects. No differences between groups could be found.

CONCLUSIONS

Axonal integrity of projections to the upper limbs is unimpaired in patients with pure HSP. The pathological mechanisms leading to spasticity and motor disability seem to be restricted to those fibres of the corticospinal pathways projecting to the lower limbs.

SIGNIFICANCE: Abnormal corticospinal function to the upper limbs seems to be incompatible with pure HSP.