title: Do patients having a decrease in SNAP amplitude during the course of MMN present with a different condition?
abstract: A decrease in sensory nerve action potentials (SNAP) amplitude has been recently reported in some patients during the course of multifocal motor neuropathy with conduction blocks (MMNCB). It is not known if those patients have different clinical expression and disability when compared with typical MMNCB. Clinical, biological and electrophysiological assessments were performed in 15 patients fitting the diagnosis criteria of MMNCB, including normal SNAP amplitude at initial examination. Patients presenting with nerve entrapment or associated disease causative of sensory neuropathy were excluded. Median time of follow-up was 3 years (1-17 years). At the last examination, four patients had at least one SNAP amplitude below 50% of normal value. None had clinically objective sensory loss. Clinical and electrophysiological data obtained at the last examination were compared between patients with normal SNAP amplitude and patients with decreased SNAP amplitude. No difference between both population in term of age, sex, disease duration, anti-GM1 antibody titers, CSF data and number of conduction blocks was noted. In contrast, patients with decreased SNAP amplitude had worse overall neuropathy limitation scale (ONLS) scores (7 vs. 2; p = 0.02), a higher number of affected nerves (12.5 vs. 4; p = 0.018), a higher number of affected limb regions (6 vs. 2; p = 0.019) and lower median CMAP amplitude (2 mV vs. 6.5 mV; p = 0.04). They were all dependent on higher doses of IVIg (1.4 g/(kg 4 weeks vs. 0.6; p = 0.018). A reduction in SNAP amplitude during the course of MMNCB is associated with a more severe disease and a more prominent axonal loss. This result needs to be confirmed in a larger cohort.
authors.affiliation: Centre de référence pour Maladies NeuroMusculaires et SLA, Hôpital Archet 1, CHU de Nice, route saint Antoine de Ginestière, BP3079, 06202 Nice Cedex 3, France. delmont.e@chu-nice.fr
authors.forename: Emilien
authors.initials: E
authors.lastname: Delmont
authors.forename: Charles
authors.initials: C
authors.lastname: Benaïm
authors.forename: Mael
authors.initials: M
authors.lastname: Launay
authors.forename: Sabrina
authors.initials: S
authors.lastname: Sacconi
authors.forename: Marie-Hélène
authors.initials: MH
authors.lastname: Soriani
authors.forename: Claude
authors.initials: C
authors.lastname: Desnuelle
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000328:Adult; D000368:Aged; D002986:Clinical Trials as Topic; D018450:Disease Progression; D004558:Electric Stimulation / Q000379:methods; D004594:Electrophysiology; D006801:Humans; D016756:Immunoglobulins, Intravenous / Q000627:therapeutic use; D007155:Immunologic Factors / Q000627:therapeutic use; D008137:Longitudinal Studies; D008875:Middle Aged; D009431:Neural Conduction / Q000502:physiology*; D011115:Polyneuropathies / Q000188:drug therapy / Q000473:pathology* / Q000503:physiopathology*; D012189:Retrospective Studies; D016896:Treatment Outcome
chemical_list: D016756:Immunoglobulins, Intravenous; D007155:Immunologic Factors