Peripheral nervous system electrodiagnostic abnormalities in predominantly Hispanic Multiple Sclerosis patients

Background: Peripheral nervous system (PNS) abnormalities in Multiple Sclerosis (MS) have been reported in case reports and small case series over the past several decades. Little is known, however, about the prevalence of electrodiagnostic abnormalities in patients with MS, including not only demyelinating neuropathies such as chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) but also axonal peripheral neuropathy and sympathetic dysfunction.

Methods: This is an observational, cross-sectional study with the objective of identifying the prevalence of the electrodiagnostic abnormalities in predominantly Hispanic MS patients in Miami, Florida. Electrodiagnostic data including nerve conduction study (NCS), electromyography (EMG) and sympathetic skin response (SSR) information was prospectively collected in 18 patients (16 females; 43.7±15.2 years) with a diagnosis of MS compared to 18 healthy (16 females; 39.9±11 years), age- and height-matched controls. The study was offered to all-comers in the MS Clinic over a period of 3 months, regardless of clinical suspicion for an underlying neuropathic process, in an effort to estimate the prevalence of abnormalities. Demographic data including age, sex, race/ethnicity was evaluated in addition to MS-specific characteristics including MS subtype, duration of disease, duration of therapy, clinical symptoms and laboratory data.

Results: There were no significant differences in baseline characteristics of patients and controls for age (p=0.4) and height (164.0±6.4 vs 162.3±4.6 centimeters; p=0.3). The mean disease duration was 106±27 months (median 107 months; range 5-336 months). The mean Expanded Disability Status Scale (EDSS) was 2.4±1.87 (median: 2.5; range 1.0-6.5). The ethnicity of patients (15 Hispanic, 3 non-Hispanic) and controls (13 Hispanic, 5 non-Hispanic; p=0.56) was similar. The frequency of electrophysiological axonal polyneuropathy (PN) was 77.8% (14/18 patients), and 85.6% of these patients had clinical sensory symptoms. Interestingly, 1 patient had previously unrecognized CIDP. All 18 patients displayed prolonged SSR latencies consistent with autonomic dysfunction. Thirteen patients (72.2%) reported autonomic symptoms such as bladder abnormalities and blood pressure fluctuations.

Conclusion: The prevalence of electrodiagnostic abnormalities, especially axonal polyneuropathy, in the MS population may be higher than traditionally considered. The relationship between axonal polyneuropathy and central axonopathy in the context of neurodegeneration in MS should be further explored. Analytic studies may identify common symptomatic and pathophysiologic etiologies to further understanding and potentially guide treatment of MS subtypes with PNS involvement.