Abstract
Klinefelter syndrome is a chromosomal disorder with a typical karyotype of 47, XXY, accompanied by various neurological symptoms. We herein report the first case of Klinefelter syndrome with a rare mosaic form of 47, XXY and 48, XXXY, combined with both spastic paraplegia and peripheral motor neuropathy. This case showed spasticity and hyperreflexia with pathological reflexes and ankle clonus as well as muscle weakness in all extremities. A motor nerve conduction study and the magnetic motor evoked potential suggested motor axonal neuropathy and corticospinal tract disorders. The present case suggests that Klinefelter syndrome can present with both upper and lower motor neuron degeneration.