To explore subclinical central nervous system (CNS) involvement in chronic inflammatory demyelinating
polyneuropathy (
CIDP), we recorded somatosensory evoked potentials (SEPs) and motor evoked potentials (MEPs) using
transcranial magnetic stimulation, to measure central sensory conduction time (CSCT) and central motor conduction time (
CMCT) and examined brain and spinal cord MRI in patients with probable
CIDP based on the American Academy of Neurology
AIDS Task Force criteria. Eighteen patients with probable
CIDP (12 males and 6 females; mean age at examination+/-SD, 45.8+/-17.0 years; range, 17-72) were included in the study. Of the 13 patients who underwent SEPs, one had prolonged CSCT (8%) and of the 13 who underwent MEPs, four had abnormal
CMCT (31%). Cranial MRI revealed five of 18 patients had abnormal scans, only one of which showed multiple ovoid periventricular lesions suggestive of
demyelination while none showed any intramedullary lesion on spinal cord MRI. Thus, 6 of the 18 patients were considered to have subclinical demyelinative CNS involvement which had lower disability on Global Neurological Disability Score (GNDS) (p=0.0061), a male preponderance (0.0537) and a larger compound muscle action potential (CMAP) amplitude in the median nerve (p=0.005) than those without. The decrease of GNDS with immunologic
therapies was nearly significant in the former (p=0.0556) but not in the latter. The results of the present study suggest that subclinical CNS involvement in
CIDP is not uncommon in Japanese patients and that
CIDP with subclinical CNS involvement is more demyelinative thus responsive to
immunotherapies while those without have more axonal damage and less responsive to
immunotherapies.