CMAP scan discontinuities: automated detection and relation to motor unit loss.

UNLABELLED: Objective To evaluate an automated method that extracts motor unit (MU) information from the CMAP scan, a high-detail stimulus-response curve recorded with surface EMG. Discontinuities in the CMAP scan are hypothesized to result from MU loss and reinnervation. METHODS: We introduce the parameter D50 to quantify CMAP scan discontinuities. D50 was compared with a previously developed manual score in 253 CMAP scans and with a simultaneously obtained motor unit number estimate (MUNE) in 173 CMAP scans. The effect of MU loss on D50 was determined with a simulation model. RESULTS: We found a high agreement (sensitivity=86.8%, specificity=96.6%) between D50 and the manual score. D50 and MUNE were significantly correlated below 80 MUs (r=0.65, n=68, p<0.001), but not when MUNE was larger than 120 MUs (r=0.23, n=59, p=0.08). CONCLUSIONS: Discontinuities in the CMAP scan as expressed by a decreased D50 are related to significant MU loss. The determination of D50 is objective, quantitative, and less time-consuming than both manual scoring and many existing MUNE methods. SIGNIFICANCE: D50 is potentially useful to monitor neurogenic disorders and moderate to severe MU loss.

Pain in Guillain-Barre syndrome: a long-term follow-up study.

BACKGROUND: Pain in Guillain-Barré syndrome (GBS) may be pronounced and is often overlooked. OBJECTIVES: To obtain detailed information about pain in GBS and its clinical variants. METHODS: This was a prospective cohort study in 156 patients with GBS (including 18 patients with Miller Fisher syndrome [MFS]). We assessed the location, type, and intensity of pain using questionnaires at standard time points during a 1-year follow-up. Pain data were compared to other clinical features and serology. RESULTS: Pain was reported in the 2 weeks preceding weakness in 36% of patients, 66% reported pain in the acute phase (first 3 weeks after inclusion), and 38% reported pain after 1 year. In the majority of patients, the intensity of pain was moderate to severe. Longitudinal analysis showed high mean pain intensity scores during the entire follow-up. Pain occurred in the whole spectrum of GBS. The mean pain intensity was predominantly high in patients with GBS (non-MFS), patients with sensory disturbances, and severely affected patients. Only during later stages of disease, severity of weakness and disability were significantly correlated with intensity of pain. CONCLUSIONS: Pain is a common and often severe symptom in the whole spectrum of GBS (including MFS, mildly affected, and pure motor patients). As it frequently occurs as the first symptom, but may even last for at least 1 year, pain in GBS requires full attention. It is likely that sensory nerve fiber involvement results in more severe pain.

Size does matter: the influence of motor unit potential size on statistical motor unit number estimates in healthy subjects.

OBJECTIVE: The statistical method of motor unit number estimation (MUNE) assumes that all motor unit potentials (MUPs) have the same size. The present study aims to evaluate the consequences of this assumption as well as its implications for the validity of statistical MUNEs. METHODS: We performed statistical and multiple point stimulation (MPS) MUNE with an array of 120 electrodes on the thenar muscles of 15 healthy subjects. These recordings allow isolation and quantification of the effect of non-uniform MUP size on MUNE, because the differences in submaximal CMAP size (and, hence, in MUNE) between electrodes are due almost entirely to differences in (summed) MUP size. RESULTS: We found no correlation between statistical and MPS MUNEs. Statistical MUNEs proved very sensitive to small variations in the "bandwidth" (variance) of the response series; MUNEs from electrodes only 8mm apart could deviate by as much as 60%. This variation in bandwidth resulted from spatial (and, hence, size) differences between the contributing MUPs. CONCLUSIONS: Statistical MUNEs are very sensitive to violation of the uniform MUP-size assumption, to an extent that blurs any correlation with MPS MUNE in healthy subjects. SIGNIFICANCE: Statistical MUNE cannot be used to detect mild to moderate motor unit losses.

Distinguishing acute-onset CIDP from fluctuating Guillain-Barre syndrome: a prospective study.

OBJECTIVE: The aim of the study was to provide criteria that can help to distinguish between GBS-TRF and A-CIDP in the early phase of disease. BACKGROUND: The distinction between Guillain-Barré syndrome (GBS) with fluctuations shortly after start of treatment (treatment-related fluctuations, or GBS-TRF) and chronic inflammatory demyelinating polyneuropathy with acute onset (A-CIDP) is difficult but important because prognosis and treatment strategy largely differ. METHODS: Patients with GBS (n = 170) were included in a prospective longitudinal study. Patients with GBS-TRF (n = 16) and patients with A-CIDP (n = 8) were analyzed and compared. Extended clinical data, biologic material, and electrophysiologic data were collected during 1 year follow-up. RESULTS: The first TRF in the GBS-TRF group always occurred within 8 weeks (median 18 days; range 10-54 days) from onset of weakness. In the GBS-TRF group, 5 (31%) patients had a second TRF and none had more TRFs. At all timepoints, patients in the A-CIDP group were less severely affected than patients with GBS-TRF, did not need artificial ventilation, rarely had cranial nerve dysfunction, and tended to have more CIDP-like electrophysiologic abnormalities. More GBS-TRF patients were severely affected and more patients had sensory disturbances when compared to the GBS group without fluctuations. CONCLUSIONS: The diagnosis of acute-onset chronic inflammatory demyelinating polyneuropathy (CIDP) should be considered when a patient thought to have Guillain-Barré syndrome deteriorates again after 8 weeks from onset or when deterioration occurs 3 times or more. Especially when the patient remains able to walk independently and has no cranial nerve dysfunction or electrophysiologic features likely to be compatible with CIDP, maintenance treatment for CIDP should be considered.