CNS Involvement in Chronic Inflammatory Demyelinating Polyneuropathy: A Visual Evoked Potential Study

Chronic inflammatory demyelinating polyneuropathy (CIDP) is considered to be an autoimmune disorder of the peripheral nervous system. Central nervous system (CNS) involvement has been clinically observed in 5% [1] and 8% [2] of patients and in many cases of CIDP, there is accompanying CNS demyelination with the presence of subclinical electrophysiological and magnetic resonance imaging (MRI) abnormalities [3-5]. In an attempt to investigate the possible existence of CNS demyelinating lesions in CIDP patients, we prospectively studied visual evoked potentials (VEPs) in 10 patients.


Introduction
Chronic inflammatory demyelinating polyneuropathy (CIDP) is considered to be an autoimmune disorder of the peripheral nervous system. Central nervous system (CNS) involvement has been clinically observed in 5% [1] and 8% [2] of patients and in many cases of CIDP, there is accompanying CNS demyelination with the presence of subclinical electrophysiological and magnetic resonance imaging (MRI) abnormalities [3][4][5]. In an attempt to investigate the possible existence of CNS demyelinating lesions in CIDP patients, we prospectively studied visual evoked potentials (VEPs) in 10 patients.

Patients and Methods
Ten patients (61.1±16.9 years, mean±SD) with CIDP, fulfilling the diagnostic criteria outlined by the Joint Task Force of the EFNS and the PNS [6] and 25 normal subjects (66.6±9.5 years) participated in this study. The clinical features of the patients are described in (Table  1). Age at examination ranged from 38 to 77 years (61.1±16.9 years) and duration of illness ranged from 4 months to 10 years. None of the patients had a history of CNS involvement. Clinical course was chronic progressive in 5 patients and relapsing-remitting in the remaining 5. Electrophysiological data were consistent with a demyelinating polyneuropathy and the etiology of the neuropathy was unknown. Patients with paraneoplastic disorders, monoclonal gammopathy, HIV, metabolic disorders, sarcoidosis, lupus erythematous, or angiitis were excluded. All patients underwent an ophthalmological examination to rule out refractive error and retinal lesions which may affect the VEP study. All patients had corrected visual acuity beyond 0.7 in each eye. CSF protein level was normal in 2 patients (20%) but over 40 mg/dl in 8 patients (range 45-135 mg/dl) without oligoclonal bands.
VEP studies were performed in all patients before and 2 and 4 weeks after treatment with intravenous immunoglobulins (IVIg). To record the VEPs, Ag/AgCl electrodes were placed at O1, Oz and O2, referred to as Fpz in the international 10/20 system. Pattern reversal VEPs were elicited using a black and white checkerboard pattern on a TV screen. The screen was subtended at an angle of 17° at the eyes and each check was subtended an angle of 1°. The mean luminance of

Abstract
The visual evoked potentials (VEPs) of 10 patients with chronic inflammatory demyelinating polyneuropathy (CIDP) and 25 normal subjects were studied to identify possible evidence of central nervous system (CNS) demyelination. VEPs were performed in each patient before and 1 month after treatment with intravenous immunoglobulins (IVIg). Prolonged P100 latency (≥mean±2SD of normal subjects) in 3 patients (30%) in at least one eye before IVIg treatment was improved in both eye stimulations after treatment. They also showed recovery of motor function after IVIg administration. MRI showed no lesions suggestive of CNS demyelination in any patients. Our findings suggest the existence of combined central and peripheral demyelinating lesions in CIDP and emphasize the possibility of a common pathogenic mechanism for both lesions.
the checkerboard was 50 cd/mm 2 with high contrast (60%). Monocular stimuli were delivered at a frequency of 1 Hz. The responses were amplified and potentials to 100 stimulations were averaged with the Neuropack MEB-2208 measurement system (Nihon-Koden, Japan). The filter window was 1-100Hz and the analysis time was 200 ms. P100 responses to independent left and right eye stimulations were recorded at O1, O2 and Oz. The P100 latency referred to the interval between the stimulus and the peak of the major positive components and the P100 amplitude referred to the peak-to-peak amplitude between N75 and P100 responses. The P100 latency and amplitude at Oz in response to left and right eye stimulation were used for comparison. Informed consent was obtained from all study participants.

Results
In the normal subjects, mean P100 latency and amplitude of the VEPs were 102.5±9.2 ms and 7.4±2.8 μV, respectively. More than 120.9 ms (mean+2SD) in P100 latency and less than 1.8 μV (mean+2SD) in amplitude were considered to be abnormal. The results for P100 latency and amplitude of the VEPs for the 10 subjects are summarized in (Table 2). Compared with the controls, 3 patients (Nos. 2, 4 and 10) had increased P100 latency preoperatively in at least one eye, which was shortened (Figure 1) in both eyes after treatment with IVIg (Table 2). After the IVIg administration, muscle weakness and cranial nerve palsy improved in all 3 patients. On the other hand, in the other 7 patients (Nos. 1, 3, 5, 6, 7, 8 and 9) P100 latency was within normal range and remained unchanged after treatment with IVIg.