Transient phrenic nerve palsy after cardiac operation in infants.

OBJECTIVE: The aims of this study were to prove the presence of transient phrenic nerve palsy in children after cardiac surgery by successive recordings of diaphragmatic action potentials (DAPs), and to decide the indication of diaphragmatic plication in infants with postoperative phrenic nerve palsy. METHODS: The DAPs were recorded from 11 infants (age 0-54 months) under artificial ventilation after cardiac surgery. The successive DAP recordings were performed within 3-4 days (0W), 1 week (1W) and 2 weeks (2W) after operation to make a final decision for diaphragmatic plication to wean artificial ventilation. RESULTS: The patients were divided into 3 groups according to the DAP changes in successive recordings, namely, patients with normal DAPs at 0W, patients with transient depression of DAPs at 0W followed by recovery to normal DAPs by 1W and/or 2W, and patients with persistent depression of DAPs of the affected side necessitating plication of hemidiaphragm. CONCLUSIONS: In infants with phrenic nerve palsy after cardiothoracic surgery, persistently abnormal DAPs in repeated electrophysiologic examinations for at least 2 weeks after surgery are a useful guidance to support clinical and radiological evidence for an indication of diaphragmatic plication.     

Middle Cerebral Artery Atherosclerosis and Deep Subcortical Infarction: A 3T Magnetic Resonance Vessel Wall Imaging Study

Background

Deep subcortical infarction is a major subtype of stroke in middle cerebral artery (MCA) territory. This study aims to evaluate the relationship between characteristics of MCA plaque and features of deep subcortical infarction.

Experimental study of a late response recorded from the thoracic wall after phrenic nerve stimulation

ObjectivesThe phrenic nerve cervical stimulation induces an early motor diaphragmatic M response that may be recorded from the 7th ipsilateral intercostal space (ICS). Some responses with prolonged latency and of unclear origin can be recorded from the same recording site. The aim of the study was to determine the electrophysiological characteristics and the neuroanatomical pathways underlying the long-latency responses (LLRs) recorded from the 7th ICS.MethodsWe studied seven healthy volunteers, five patients with spinal cord injury and five patients with diaphragmatic palsy. All underwent phrenic nerve conduction study. An LLR was sought for at different stimulation sites using various stimulus intensities.ResultsA polyphasic LLR was recorded from the 7th ICS in all healthy subjects. It was mainly elicited by nociceptive stimulations, not only of the phrenic, but also of the median nerves. Its latency was longer than 70 ms, with a wide inter- and intra-individual variability. Amplitude was highly variable and some habituation phenomenon occurred. The LLR was retained in most tetraplegic patients after phrenic nerve stimulation, but absent otherwise. It was present in all patients with diaphragmatic palsy after phrenic nerve stimulation.ConclusionThe LLR is likely to be produced by both intercostal and diaphragm muscles. It is a polysynaptic and multisegmental spinal response, probably conveyed by small-diameter nociceptive A-δ and/or C fibres and modulated by a supraspinal control.SignificanceThe LLR recorded from the chest wall may constitute, by analogy with the nociceptive component of the lower limb flexion reflex in humans, a protective and withdrawal spinal reflex response.     

Assessment of corticodiaphragmatic pathway and pulmonary function in acute ischemic stroke patients.

This study investigates the effect of stroke on the corticodiaphragmatic pathway and attempts to clarify the relationship between neurophysiological data and degree of motor disability, site of infarction in computerized tomography (CT) scan, diaphragmatic excursion, blood gases and pulmonary function in stroke patients. Using magnetic stimulation of the scalp sites and cervical roots, an assessment of corticodiaphragmatic pathway was made. The study included 34 sequentially selected patients from a total of 250 patients with acute ischemic stroke. Twenty-five (age- and sex-matched) volunteers served as controls. Sixteen patients had cortical infarction, 13 had subcortical infarction and five had both cortical and subcortical infarction. The mean according to the Scandinavian Stroke Scale was 32.2. Decreased diaphragmatic excursion was observed in 41% of the patients. Twenty-four patients (70.5%) had abnormal magnetic evoked potentials (MEPs) in the affected hemisphere. In five patients MEPs could not be elicited from the affected hemisphere; the remaining 19 patients had abnormal values of both cortical latency and central conduction time (CCT). Cortical latency, CCT, amplitude of compound muscle action potentials (CMAPs) and excitability threshold of the affected hemisphere were significantly altered compared with both the unaffected hemisphere and the control group. Those patients with hemiplegia had a greater degree of hypoxia, hypocapnia and decreased serum bicarbonate level compared with the control group. Also, hemiplegic patients had different degree of respiratory dysfunction. A statistically significant association was found between neurophysiological data and disability score, diaphragmatic excursion, site of infarction in CT scan and degree of respiratory dysfunction. Central diaphragmatic impairment may occur in acute stroke and could contribute to the occurrence of hypoxia in those patients.     

Phrenic Nerve Stimulation for Diaphragm Pacing in a Quadriplegic Patient

Chronic hypoventilation due to injury to the brain stem respiratory center or high cervical cord (above the C3 level) can result in dependence to prolonged mechanical ventilation with tracheostomy, frequent nosocomial pneumonia, and prolonged hospitalization. Diaphragm pacing through electrical stimulation of the phrenic nerve is an established treatment for central hypoventilation syndrome. We performed chronic phrenic nerve stimulation for diaphragm pacing with the spinal cord stimulator for pain control in a quadriplegic patient with central apnea due to complete spinal cord injury at the level of C2 from cervical epidural hematoma. After diaphragmatic pacing, the patient who was completely dependent on the mechanical ventilator could ambulate up to three hours every day without aid of mechanical ventilation during the 12 months of follow-up. Diaphragm pacing through unilateral phrenic nerve stimulation with spinal cord stimulator was feasible in an apneic patient with complete quadriplegia who was completely dependent on mechanical ventilation. Diaphragm pacing with the spinal cord stimulator is feasible and effective for the treatment of the central hypoventilation syndrome.     

Paroxysmal apnea and vasomotor instability following medullary infarction

BACKGROUND: Central hypoventilation and paroxysmal hypertension are uncommon complications of medullary infarction. To our knowledge, the combination of these autonomic complications of medullary stroke has not previously been reported. OBJECTIVE: To describe a patient who experienced life-threatening paroxysmal attacks of central apnea and vasomotor instability 3 months after medullary infarction, a combination of symptoms that is unusual. PATIENT, METHODS, AND RESULTS: Following a right lateral medullary infarction, an otherwise stable 70-year-old woman developed recurrent episodes of apnea (PCO2), > 100 mm Hg), blood pressure instability (systolic blood pressure, > 200 to < 100 mm Hg), and mental status changes (from agitation to coma) within hours of removal from mechanical ventilation. These attacks occurred repeatedly after removal from mechanical ventilation and were prevented by diaphragm pacing with a phrenic nerve pacemaker and nocturnal mechanical ventilation via a tracheostomy. CONCLUSIONS: A syndrome of life-threatening central hypoventilation and vasomotor instability can occur after medullary infarction. Placement of a phrenic nerve pacemaker can prevent these complications, without the functional limitations imposed by continuous mechanical ventilation.     

Assessment of corticodiaphragmatic pathway and pulmonary function in acute ischemic stroke patients

The aims of this study were to investigate the effect of stroke on the corticodiaphragmatic pathway and to clarify the relationships between neurophysiological data and degree of motor disability, site of infarction in CT scan, diaphragmatic excursion, blood gases and pulmonary function in stroke patients. The corticodiaphragmatic pathway was assessed using magnetic stimulation of the scalp sites and cervical roots. The study included 34 sequentially selected patients out of 250 patients with acute ischemic stroke. Twenty-five (age and sex matched) volunteers served as controls. Sixteen patients had cortical infarction, thirteen had subcortical infarction and five had both cortical and subcortical infarction. The mean Scandinavian Stroke Scale was 32.2. Decreased diaphragmatic excursion was observed in 41% of the patients. Twenty-four patients (70.5%) had abnormal magnetic evoked potentials (MEPs) of the affected hemisphere. In five patients MEPs were unelicitable from the affected hemisphere. The remaining nineteen patients had abnormal values of both cortical latency and central conduction time (CCT). Cortical latency, CCT, amplitude of compound muscle action potentials (CMAPs) and excitability threshold of the affected hemisphere were significantly altered compared to both the unaffected hemisphere and the control group. The patients with hemiplegia had a greater degree of hypoxia, hypocapnia and decreased serum bicarbonate level compared to the control group. Additionally, hemiplegic patients had a different degree of respiratory dysfunction. A statistically significant association was found between neurophysiological data and disability score, diaphragmatic excursion, site of infarction in CT scan and degree of respiratory dysfunction. Central diaphragmatic impairment may occur in acute stroke and could contribute to the occurrence of hypoxia in those patients.     

Isolierte,unilaterale Parese des N. phrenicus nach Pneumonie und Pleuritis

Unilateral diaphragmatic paralysis has many causes. Tumor and trauma are the two most frequent identifiable causes. Infectious processes involving the lung and/or mediastinum may result in temporary or permanent diaphragmatic paralysis. We report the case of an 81-year old man who suffered from right-sided pneumonia followed by a period of several months with exertion dyspnea. Radiological examinations showed an elevated right diaphragm, abnormal restrictive lung function, and impaired diaphragmatic muscle strength. The neurophysiological studies provided evidence of a partial phrenic nerve lesion. We discuss the differential diagnosis of isolated phrenic nerve lesions with particular regard to infections.     

Intracortical inhibition and facilitation of the response of the diaphragm to transcranial magnetic stimulation.

Respiratory muscles respond to a subcortical automatic command and to a neocortical voluntary command. In diseases such as stroke or motor neurone disease, an abnormal diaphragmatic response to single transcranial magnetic stimuli can identify a central source for respiratory disorders, but this is not likely to be the case in disorders affecting intracortical inhibitory and facilitatory mechanisms. This study describes the response of the diaphragm to paired transcranial magnetic stimulation. Thirteen normal subjects were studied (age range, 22 to 43 years; 7 men; phrenic conduction, <6.8 msec; latency of diaphragmatic motor evoked potential, <20.5 msec). Motor evoked potentials in response to paired stimulation were obtained in eight subjects only, with the motor threshold in the remaining five subjects too high to absorb the loss of power inherent in the double-stimulation montage. Interstimulus intervals less than 5 msec resulted in a statistically significant inhibition (p < 0.01 for interstimulus intervals of 1 and 3 ms), whereas intervals longer than 6 msec were facilitatory (maximal, 15 msec). The diaphragmatic pattern matched that of the biceps brachii. The authors conclude that it is possible to study intracortical inhibition and facilitation of diaphragmatic control, although not in all subjects. Technical improvement should alleviate current limitations and make paired transcranial magnetic stimulation a tool to study respiratory muscle abnormalities in settings in which intracortical interactions are important, such as movement disorders.     

Phrenic nerve conduction study in demyelinating neuropathies and open-heart surgery.

OBJECTIVES: The aim of this study was to determine normal values of phrenic nerve conduction (PNC) in healthy individuals; to evaluate the subclinical extent of phrenic nerve involvement in Guillain-Barré syndrome (G-B) and hereditary motor and sensory neuropathy-I (HMSN-I), and to evaluate phrenic nerve damage after cardiac surgery. MATERIALS AND METHODS: PNC was performed by transcutaneous stimulation in the neck and recording the diaphragmatic potential from surface electrodes placed at the seventh and eight intercostal spaces. PNC was performed bilaterally in 25 healthy volunteers and 25 patients before and after open-heart surgery. Right PNC was also performed in 5 cases with G-B and 5 patients with HMNS-I. RESULTS: Latency and amplitude of the diaphragmatic potential were the same in controls and in patients with cardiac disease before surgery. After surgery, 28% of patients had left phrenic nerve inexcitability, and 8% had reduced amplitude of the response. These 9 patients demonstrated elevation of the left hemidiaphragm on chest radiography. Left PNC performed 1 year after the operation showed improvement in latency and amplitude of the responses in all except one patient. PNC was prolonged in 4 out of 5 cases with G-B and in all patients with HMNS-I. CONCLUSIONS: PNC is an easy and reliable method in evaluating phrenic nerve damage due to hypothermia or primary stretch injury in patients after cardiac surgery. PNC may be helpful in detecting diaphragmatic involvement before clinical ventilatory insufficiency in demyelinating neuropathies such as G-B and HMNS-I.     

大脑中动脉狭窄与其深穿支供血区单发脑梗死的关系

目的 分析大脑中动脉(MCA)深穿支供血区单发脑梗死的形态学表现,进一步探讨其与MCA狭窄的关系.方法 连续入选2005年1月至2006年12月于北京协和医院神经科住院治疗急性脑梗死,并经头颅DWI检查明确急性梗死灶为单发,且位于MCA深穿支供血区域的55例患者;所有患者均行TCD和MRA检查,颅外颈内动脉狭窄>50%以及有可疑心源性栓子来源的患者从研究中排除.根据是否存在病灶同侧MCA狭窄将入选患者分为两组:MCA狭窄组(14例)与MCA正常组(41例).测量DWI上急性梗死灶的直径、面积和体积,并将直径≤2 cm归为经典腔隙性梗死,直径>2 cm归为纹状体内囊梗死.DWI上的梗死灶区分为基底节区、侧脑室体旁和同时累及上述2个部位,并判断MRI T2>像上皮质下多发陈旧性小梗死灶或白质疏松是否存在.结果 55例患者中,病灶侧MCA狭窄患者14例(25.5%),MCA正常患者41例(74.5%).MCA狭窄组中经典腔隙性梗死占71.4%,MCA正常组中经典腔隙性梗死占67.3%,差异无统计学意义(χ2=0.147,P=0.701).MCA狭窄组与正常组患者MCA深穿支梗死病灶的大小(包括直径、面积及体积)差异均无统计学意义.MCA正常组和MCA狭窄组病灶在基底节区、侧脑室体旁及基底节区+侧脑室体旁分布的比例依次为:正常组31.7%、17.1%和51.2%;狭窄组35.7%、28.6%和35.7%,两组间差异无统计学意义(χ2=1.272,P=0.529).同时存在皮质下多发陈旧性小梗死灶或白质疏松的患者在MCA正常组有23例(56.1%),在MCA狭窄组有3例(21.4%),二者差异有统计学意义(χ2=5.033,P=0.025).结论 MCA深穿支供血区梗死具有不同的发病机制,MCA狭窄和穿支动脉本身病变均可造成深穿支供血区单发脑梗死.梗死灶的大小、体积及梗死发生的部位与是否存在同侧大脑中动脉狭窄无明显相关性,而同时存在皮质下多发陈旧性小梗死灶或白质疏松对穿支动脉病变有提示作用.     

The role of cervical afferent nerve fiber inhibition of the crossed phrenic phenomenon

High cervical spinal cord hemisection produces a permanent paralysis of the ipsilateral hemidiaphragm. In many species, function is restored to this paretic hemidiaphragm if the contralateral hemidiaphragm is paralyzed by transecting the phrenic nerve. This response is termed the “crossed phrenic phenomenon.” The present study determines the long-term effects on diaphragmatic function after anesthetization or crushing the contralateral phrenic nerve, or after cutting its dorsal roots in rats subjected to a high cervical spinal cord hemisection. Dorsal root transection was the only procedure which resulted in a partial functional recovery of the hemidiaphragm paralyzed by the spinal cord hemisection without a loss of function in the contralateral hemidiaphragm. The results suggest that afferent nerve fibers in the contralateral phrenic nerve may normally inhibit the functional expression of the crossed phrenic pathway, although the precise mechanism for this inhibition is not yet known.     

Unusual manifestation of heat stroke: Isolated trochlear nerve palsy

Heat stroke is a life-threatening disease characterized by hyperthermia and neurological dysfunction. The central nervous system is highly sensitive to hyperthermia, which causes neurological complications due to the involvement of the cerebellum, basal ganglia, anterior horn cells, and peripheral nerves. Several studies reported about clinical symptoms and brain image findings of heat stroke. Isolated cranial nerve dysfunction caused by lacunar infarction is an extremely rare condition in patient with heat stroke. We experienced a rare case of trochlear nerve palsy due to midbrain infarction caused by heat stroke.     

Phrenic nerve palsy associated with birth trauma – Case reports and a literature review

Phrenic nerve palsy is a peripheral nerve disorder caused by excessive cervical extension due to birth trauma or cardiac surgery. We describe two new patients with phrenic nerve palsy associated with birth trauma. Both patients exhibited profound dyspnea and general hypotonia immediately after birth. A chest roentgenogram and fluoroscopy revealed elevation of the diaphragm, leading to a diagnosis of phrenic nerve palsy associated with birth trauma. Since they had intermittently exhibited dyspnea and recurrent infection, we performed video-assisted thoracoscopic surgery (VATS) plication in both cases, at an early and a late stage, respectively. Both patients subsequently exhibited a dramatic improvement in dyspnea and recurrent respiratory infection. Interestingly, the late stage operated infant exhibited spontaneous recovery at 7 months with cessation of mechanical ventilation once. However, this recovery was transient and subsequently led to an increased ventilation volume demand, finally resulting in surgical treatment at 15 months. Histological examination of the diaphragm at this time showed grouped muscle atrophy caused by phrenic nerve degeneration. To our knowledge, this is the first pathologically proven report of grouped muscle atrophy of the diaphragm due to phrenic nerve degeneration, suggesting that partial impairment of phrenic nerves resulted in respiratory dysfunction with incomplete recovery. We conclude that recently developed VATS plication is a safe and effective treatment for infants with phrenic nerve palsy, and should be considered as a surgical treatment at an early period.     

Computed tomography findings in the first few hours of ischemic stroke: implications for the clinician

In order to evaluate the clinical usefulness of emergency computed tomography (CT) in acute ischemic stroke, we assessed whether CT findings within the first few hours of stroke onset reliably predict type, site and size of the index infarction, and risk of death or disability. For this reason we reviewed clinical and CT findings in a cohort of unselected consecutive patients referred to the stroke unit of a large urban hospital because of a presumed ischemic stroke in the anterior circulation (AC), and submitted to CT within 5 h from onset. Out of 158 total patients, emergency CT revealed parenchymal changes compatible with AC focal ischemia in 77 (49%) and a hyperdense middle cerebral artery (MCA) in 41 (26%). Parenchymal changes and hyperdense MCA predicted an AC territorial infarction respectively in 97% of cases (95% C.I. 93% to 100%) and in 95% of cases (95% C.I. 88% to 100%). Site and size of early changes coincided with those of final lesions in 79% of patients with cortical changes and in 95% of patients with cortico-subcortical changes, but only in 37% of patients with initial subcortical changes, the remainder of whom developed a cortico-subcortical infarction. At logistic regression parenchymal changes were the only independent predictor of an AC territorial infarction. Negative predictive power, however, was only 40% (95% C. I. 29% to 51%) for parenchymal changes, and 35% for hyperdense MCA (95% C.I. 26% to 44%). The odds for death or disability at 1 month associated with parenchymal changes were thrice as high as with negative CT, even after adjustment for clinical severity on admission. These results indicate that CT scan adds significantly to the prediction of outcome made on clinical grounds. The frequent development of a territorial infarction in patients with initially negative CT and the subsequent recruitment of the cortex in those initially exhibiting only subcortical changes suggest that the transition from ischemia to infarction often occurs after the first five h following stroke.     

Bleeding and subsequent anemia: a precipitant for cerebral infarction

BACKGROUND AND OBJECTIVES: The relationship between bleeding and subsequent anemia (BSA) and the occurrence of stroke has not been sufficiently studied. The purpose of the present study was to elucidate the characteristics of stroke associated with BSA. METHODS: We studied 16 consecutive patients with acute stroke associated with anemia (hemoglobin level on admission < or =9.0 g/dl) and compared their stroke subtypes with those of 32 control subjects. RESULTS: The cause of anemia was upper gastrointestinal bleeding in 11 patients (ulcers in 8; carcinomas in 2, and hemorrhagic gastritis in 1), bleeding from a hemorrhoid in 2, uterine cervical bleeding in 1, ecchymosis probably related to medication in 1, and chronic blood drainage in 1. At least 10 patients had a history of recent (<1 week), active bleeding. Clinical and imaging studies showed that all the patients had infarcts and none had intracerebral hemorrhages. Thirteen patients had infarcts in the region of the middle cerebral artery (MCA) (total MCA region in 2; partial, cortical area in 5; subcortical area in 5, and lenticulostriate artery region in 1), 2 had anterior cerebral artery (ACA) region infarction, and 1 had cerebellar infarction. All 11 patients who underwent vascular imaging studies showed significant stenosis and/or occlusion of the internal carotid artery (ICA) (n = 5), the MCA (n = 4), both the ICA and MCA (n = 1), or the ACA (n = 1). Of the different stroke subtypes (large vessel infarction (LVI), small vessel infarction, cardiogenic embolic infarction, intracerebral hemorrhage), LVI was significantly (p<0.05) more frequent in patients with stroke associated with BSA than in the controls, even though the demographics and risk factors were similar in each group. CONCLUSIONS: The close temporal relationship between the bleeding and the onset of stroke, as well as the predominance of the LVI subtype in the BSA-associated group as compared to controls, suggest that BSA may precipitate atherothrombotic cerebral infarction. A hemodynamic alteration, enhanced thrombosis or a combination of these appears to be the pathogenic mechanism.     

A comprehensive electrophysiological evaluation of phrenic nerve injury related to open-heart surgery

A prospective electrophysiological study of phrenic nerve was performed in 59 subjects undergoing open-heart surgery. The nerve was stimulated percutaneously at the neck and the diaphragmatic response was recorded with surface electrodes placed over the 8th intercostal space. The latency, amplitude, duration and area of the evoked response were measured before and after the operation. Post-operatively no response was elicited in 2 patients bilaterally, in 5 from the left and in 2 from the right. Comparison of the post-operative with the pre-operative group values in the remaining subjects showed that the amplitude and area of the left phrenic were lower in the post-operative study, indicating that some of the nerve fibres were not conducting. There were no statistically significant differences between pre and post-operative values of latency or duration on the left or any of the parameters on the right. Our findings suggest that the amplitude and area of the diaphragmatic response are more sensitive than latency in detecting phrenic nerve paresis associated with open-heart surgery.     

Silent cortical neuronal damage in atherosclerotic disease of the major cerebral arteries

In atherosclerotic internal carotid artery (ICA) or middle cerebral artery (MCA) disease, hemodynamic compromise may cause selective neuronal damage manifested as loss of central benzodiazepine receptors (BZRs) in the normal-appearing cerebral cortex, without overt episode of stroke. To investigate the association of decreases in cortical BZRs with hemodynamic compromise and the effect of angiotensin receptor blockers (ARBs) on these receptors in patients whose atherosclerotic ICA or MCA disease is asymptomatic, we measured BZRs using positron emission tomography and ¹¹C-flumazenil in 79 patients with asymptomatic atherosclerotic ICA or MCA disease and no cortical infarction. Three-dimensional stereotactic surface projections were used to calculate the BZR index, a measure of abnormally decreased BZRs in the cerebral cortex within the MCA distribution. Multiple regression analysis showed this index to be positively correlated with the value of oxygen extraction fraction, with the presence of silent subcortical infarcts, and with the presence of ischemic heart disease, whereas it was negatively correlated with the treatment of hypertension with ARBs. In asymptomatic atherosclerotic ICA or MCA disease, hemodynamic compromise is associated with selective neuronal damage manifested as decreases in cortical BZRs in the noninfarcted cerebral cortex, whereas ARBs are associated with preservation of cortical BZRs.     

Dense middle cerebral artery sign: an indicator of poor outcome in middle cerebral artery area infarction.

Thirteen patients with a dense appearance of the horizontal part of the middle cerebral artery (MCA) "dense middle cerebral artery sign" in CT scans taken within 24 hours after onset of ischaemic stroke had considerably poorer prognosis than controls with stroke, but without the sign. A hyperdense appearance of the MCA is known to be associated with thromboembolism, but dense middle cerebral artery sign is also an early warning of a large infarction, brain oedema and poor prognosis in infarction in the MCA area.     

A prospective evaluation of phrenic nerve conduction in multifocal motor neuropathy and chronic inflammatory demyelinating polyneuropathy

The purpose of the study was to evaluate electrophysiologically phrenic nerve involvement in multifocal motor neuropathy (MMN) and chronic inflammatory demyelinating polyneuropathy (CIDP). The response latencies following phrenic nerve stimulation were increased in 11 of 14 (80%) patients in the CIDP group but in only 1 of 14 (8%) patients in the MMN group. The mean diaphragmatic compound muscle action potential (CMAP) was significantly lower in amplitude in the CIDP group compared to the MMN group and to a control group of 8 subjects (P < 0.001). There were no significant differences between the MMN and control groups. Only the reduction in CMAP amplitude correlated with the presence of restrictive lung function. Phrenic nerve conduction measurement should be performed more systematically, especially in CIDP and, when diaphragmatic CMAPs are reduced in amplitude, pulmonary function tests should be performed to look for a restrictive lung syndrome.