Reduced Compound Muscle Action Potential Research Articles

Central and peripheral respiratory electrophysiological studies in myotonic dystrophy.

Acute and chronic respiratory failure is a common and potentially life-threatening feature in patients with myotonic dystrophy (MD). The causes may be varied, and can involve both the central and peripheral nervous system. To evaluate the incidence of respiratory muscle involvement and the function of the central motor inspiratory pathway to phrenic motor neurons we performed magnetic stimulation of the cortex and cervical spinal cord, phrenic nerve conduction studies and needle EMG of diaphragm and intercostal muscles in 25 patients with MD. The results were compared with those from 35 healthy subjects. In addition, pulmonary function tests, blood gas analyses and static mouth pressures were evaluated. Abnormalities in response to magnetic stimulation, including a reduced compound muscle action potential (CMAP) from the diaphragm and increased excitability threshold, indicated impaired central inspiratory drive in 20% of cases. Phrenic nerve conduction showed a reduced diaphragmatic CMAP amplitude in 20%, and a delayed negative peak onset latency in 4% of cases. Abnormalities in diaphragm and intercostal muscle needle EMG were found in 76% of cases, these were mainly myotonic discharges (68%) and a decrease in the number of active motor units (36%). Patients with abnormal respiratory electrophysiological parameters had a significantly lower functional vital capacity (FVC; P = 0.005). The duration of the disease correlated negatively with diaphragmatic CMAP amplitude to phrenic nerve, but not magnetic, stimulation. Our results demonstrate that the involvement of the central inspiratory pathway is common in MD patients. Central and peripheral electrophysiological studies of the diaphragm should be considered in the diagnosis and management of patients with MD and dyspnoea.

Brainstem reflexes in patients with olivopontocerebellar atrophy

In 4 patients with familial olivopontocerebellar atrophy (OPCA) we have recently described an abnormal movement of facial muscles characterized by rhythmic muscle twitching during voluntary activation (facial action myoclonus). In the present article, we present the results of a neurophysiological study of brainstem reflexes in those 4 patients, in 4 other patients with OPCA but without facial action myoclonus, in 3 patients with pure cerebellar cortical atrophy, and in 6 normal volunteers used as control subjects. All patients had similar clinical features, but only the patients with facial action myoclonus and only one of the other patients with OPCA had brainstem atrophy detected on magnetic resonance imaging. Electrophysiological abnormalities were found in all patients with facial action myoclonus and consisted of myokymia in perioral muscles at rest, spread of spontaneous and reflex blinking to the orbicularis oris, and enhanced long-latency facial reflex responses to stimuli applied to the facial or trigeminal nerve. Other relevant electrophysiological abnormalities were the absence of jaw jerk in 2 patients, the absence of an R1 response of the blink reflex in 1 patient, and a markedly reduced compound muscle action potential of the facial nerve in another patient. Comparable electrophysiological abnormalities were found in only 1 of the patients with OPCA but without facial action myoclonus, and in none of the patients with pure cerebellar cortical atrophy. Facial action myoclonus is a clinical manifestation of a global brainstem functional derangement that may characterize a subgroup of patients with OPCA or constitute a distinctive step in the natural evolution of some forms of the disease.

In vivo effects of sera from Guillain‐Barré subgroups: An electrophysiological and histological study on rat nerves

Serum from 20 patients with Guillain-Barré syndrome (GBS), 10 healthy controls and 10 patients with recent cytomegalovirus, Epstein-Barr virus, or Campylobacter jejuni/coli infections was injected into rat sciatic nerve. The 20 GBS patients consisted of 2 groups of 10 patients with different electrophysiological and clinical disease patterns. The main aim of the study was to investigate possible differences in humoral (auto)-immunity between these subgroups. We found no statistically significant differences in electrophysiological or histological parameters between nerves injected with sera from the 2 GBS groups. The sera of the GBS groups caused significantly more compound muscle action potential reduction at 3 to 5 days postinjection than the healthy control sera. No significant difference in nerve conduction was found between nerves injected with GBS serum and serum of patients with proven infections without GBS. Histological analysis of the same nerves that were studied electrophysiologically showed no significant differences in demyelination or other histological parameters between patients and controls at 5 days postinjection. Based on the findings in this study that sera of GBS groups with important differences in disease pattern and sera of patients with proven infection but without GBS show similar in vivo effects on rat nerves, we suggest it may be more likely that these effects are caused by aspecific serum factors associated with immune-system activation, especially by precedent infections, than by specific disease-related factors such as anti-myelin antibodies.