Multifocal slowing of nerve conduction in metachromatic leukodystrophy.

Polyneuropathy is invariably associated with the late-infantile form of metachromatic leukodystrophy (MLD), and occurs frequently in the early juvenile, juvenile, and adult variants. Uniform slowing of nerve conduction velocity is the neurophysiologic hallmark of metachromatic leukodystrophy and other inherited demyelinating polyneuropathies. To evaluate the consistency of this principle, we reviewed nerve conduction studies in 9 children with late-infantile or early-juvenile metachromatic leukodystrophy. Each child had significant slowing of motor nerve conduction velocity (NCV). The compound muscle action potentials showed abnormal temporal dispersion in 3 of the 9 children, which is usually regarded as the hallmark of acquired demyelinating polyneuropathies. There are reports of multifocal slowing in other hereditary processes including X-linked Charcot-Marie-Tooth disease, hereditary neuropathy with liability to pressure palsies, and adrenomyeloneuropathy. Although multifocal NCV slowing in a child with polyneuropathy is seen most commonly in acquired conditions, a hereditary process, including MLD, cannot always be excluded in this setting.