Utility of somatosensory evoked potentials in the assessment of response to IVIG in a long-lasting case of chronic immune sensory polyradiculopathy

Abstract

Background: Chronic immune sensory polyradiculopathy (CISP) identifies a progressive acquired peripheral dysimmune neuropathy recognized as a chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) variant. We describe a young woman with a thirteen-year history of CISP with a belated variable response to intravenous immunoglobulin (IVIG) and an almost erratic anticipation of symptoms between IVIG cycles. The association of IVIG and corticosteroids, immunosuppressants, plasmapheresis, did not lead to clinical improvement and was characterized by significant side effects. We evaluated a combined clinical and somatosensory evoked potentials (SSEPs) approach aimed to identify possible predictive parameters concerning the effect and duration of each IVIG administration. Neurologic disability was evaluated using INCAT - Overall Disability Sum Score (INCAT-ODSS).

Case presentation: A 30-year-old woman presented on 2004 for the subacute onset of asymmetric paresthesias in the lower limbs over the previous six months. The symptoms had been relapsing-remitting during the first four months, followed by a slow progression, resulting in limbs ataxia and a progressive gait disturbance requiring Canadian crutches. Motor and sensory nerve conduction studies and electromyographic evaluation were into normal limits. Median SSEPs were normal, while tibial SSEPs were characterised by the bilateral absence of both lumbar and cortical responses. Cerebrospinal fluid detected an increased protein concentration, while spinal MRI showed a pronounced thickening of the sacral nerve roots, together with a tube-shaped enlargement. These findings led to the diagnosis of CISP and the patient was treated with IVIG reaching a stable remission over the following 9 years. In early 2014, the patient began to show a variable response to treatment with erratic anticipation of sensory disturbances, and a more pronounced walking disability: corticosteroids, plasmapheresis, mycophenolate mofetil and cyclophosphamide were uneffective and burdened by relevant side effects. To better assess the response to IVIG in terms of time-effect, consistency and duration, we have combined a scheduled clinical and SSEPs evaluation during and after each IVIG cycle.

Conclusions: The correlation between the neurophysiological data and the INCAT-ODSS scores has allowed the modulation of IVIG cycles with a significant reduction of the clinical fluctuations and disability. SSEPs may therefore represent an useful and recommended additional aid for the treatment schedule of this rare clinical form.

Keywords: Chronic immune sensory polyradiculopathy; Chronic inflammatory demyelinating polyneuropathy; INCAT - Overall disability sum score; Intravenous immunoglobulin; Somatosensory evoked potentials.

Fig. 1

Spinal MRI study. MR coronal STIR (a), sagittal STIR (b) and T2-weighted sagittal (c) images of the cauda equina showing marked thickening of the nerve roots together with a tube-shaped enlargement. (R = right; L = left; A = anterior; P = posterior)

Fig. 2

Sural nerve biopsy. Cross section of plastic embedded left sural nerve stained with Toluidin blue showing slight axonal impairment without inflammatory infiltrate, a minimal reduction in myelinated fibers density with some isolated aspects of chronic (cluster) reinnervation (white arrow) and sporadic fibers in Wallerian

Fig. 3

Superimposed graphs of the daily ODSS and the longitudinal trend of tibial SSEPs (N22 and P40 latencies) recorded every 7 days over a period of 16 consecutive weeks. The bold lines below the horizontal axis refer to each cycle of IVIG scheduled every 28 days. Note the large P40 latencies fluctuations significantly correlated to the highest ODSS values

Fig. 4

Example of SSEPs pattern recorded at the 28th-day control after an IVIG cycle. Upper traces: SSEPs from median nerve stimulation show normal responses. Lower traces: SSEPs from tibial nerve stimulation show absence of both the peripheral and cortical responses

Fig. 5

Superimposed graphs of the daily ODSS and the longitudinal trend of tibial SSEPs (N22 and P40 latencies) recorded the first day of each IVIG administration and after 7–14 days for 13 consecutive recordings. The bold lines below the horizontal axis refer to each cycle of IVIG scheduled every 18 days. Note the relevant stabilization of P40/N22 latencies and the reduction of ODSS values

Fig. 6

Example of SSEPs pattern recorded at the 18th-day control after an IVIG cycle. Upper traces: SSEPs from median nerve stimulation show normal responses. Lower traces: SSEPs from tibial nerve stimulation show the presence of both the peripheral (N22) and cortical (P40) response, although the latter with increased latency