Key words: amyotrophic lateral sclerosis; motor neuron disease; respiratorySHORT REPORTfailure; electrophysiology; diaphragm

MUSCLE NERVE 20:517–519 1997

MOTOR NEURON DISEASE PRESENTINGAS ACUTE RESPIRATORY FAILURE:ELECTROPHYSIOLOGICAL STUDIES

ROBERT CHEN, MBBChir, MSc, FRCPC,1

FRANCOIS GRAND’MAISON MD, FRCPC,2

JOHN D. BROWN, MD, FRCPC,1 and CHARLES F. BOLTON, MD, FRCPC1*

1 Department of Clinical Neurological Sciences, London Health Sciences Centre,University of Western Ontario, Victoria Campus, 375 South Street, London,Ontario, Canada N6A 4G52 Department of Neurology, University of Sherbrooke, Sherbrooke, Quebec, Canada

Received 18 September 1996; accepted 18 October 1996

Respiratory failure usually occurs late in the course symptoms of limb weakness, although all had variablecombinations of wasting, fasciculation, or weaknessof motor neuron diseases (MND) and is the most

important cause of death. However, in a small on physical examination. Blood gases prior to intuba-tion all showed hypercapnia. Four patients (cases 2,number of patients with MND, respiratory involve-

ment occurs early and some even present as acute 3, 4, and 6) had only lower motor neuron signs andwere diagnosed as progressive muscular atrophy, 3respiratory failure.3,7–9,13 Although early diaphrag-

matic involvement is often suspected as the cause (cases 1, 5, and 7) had both upper and lower motorneuron signs and were diagnosed as amyotrophicof respiratory failure, electrophysiological studies

of the respiratory system in this group of patients lateral sclerosis (ALS). None of the patients was suc-cessfully weaned from the ventilator. Five patientshave not been previously reported. We report here

the electrophysiological studies of 7 patients with (cases 1, 2, 3, 6, and 7) elected to discontinue assistedventilation and died of respiratory failure. One (caseMND who presented with acute respiratory failure.

We found that phrenic nerve conduction studies 3) died of an unrelated condition and 1 (case 5) wasalive on a home ventilator. Postmortem examinationand needle electromyography (EMG) of the dia-

phragm were useful in determining the extent of in cases 1, 2, 3, and 7 revealed severe loss of anteriorhorn cells in the cervical cord. The corticospinalrespiratory involvement.tracts were normal or showed only minimal changesand microscopic examination of the motor cortexPATIENTS AND METHODSwas normal. Details of the clinical and pathologicalWe studied 7 patients (4 male and 3 female, meanfeatures of these patients have been reported.3

age 66, range 48–77) who presented with acute respi-Needle EMG of the diaphragm and phrenic nerveratory failure requiring mechanical ventilation. In

conduction studies were performed as previously de-none of them was a neuromuscular disorder pre-scribed.1,2

viously diagnosed or suspected. The duration of re-spiratory symptoms such as dyspnea on exertion or

RESULTSorthopnea ranged from 2 weeks to 12 months. Allpatients except case 4 were ambulatory at the time Nerve Conduction Studies. Motor conduction ve-

locities in limb nerves were normal or mildly reducedof presentation and only 3 (cases 1, 2, and 4) had(.80% of lower limit of normal). The phrenic distalmotor latencies were normal or mildly prolonged tothe range of 9–11 ms (normal limit 8.1 ms). In 5*Correspondence to: Dr. Charles F. Boltonpatients (cases 1, 3, 5, 6, and 7), the compound mus-CCC 0148-639X/97/040517-03

1997 John Wiley & Sons, Inc. cle action potentials (CMAPs) from limbs muscles

Short Reports MUSCLE & NERVE April 1997 517

were normal or mildly reduced but phrenic CMAPs conduction studies, which fulfilled the diagnostic cri-teria for MND.5,15 The motor conduction velocitieswere severely reduced (,50% of the lower limit ofin limb nerves were normal or only mildly reduced,normal) or absent. In 2 patients (cases 2 and 4), theconsistent with previous reports.4CMAPs of both the limb and phrenic nerves were

We have further developed the techniques ofseverely reduced, but more so in the phrenic nerves.phrenic nerve conduction study and needle EMGSensory nerve conduction studies were normal inof the diaphragm and found them useful in the in-all patients.vestigation of neuromuscular respiratory failure.1,2,12

Phrenic nerve conduction studies in our patients in-Needle EMG. The results are summarized in Tablevariably showed low-amplitude or absent responses1. There was widespread denervation in limb musclesfrom both diaphragms. These findings are suggestivein all patients. In cases 1 and 6 the levator scapulaeof severe diaphragmatic weakness, as the CMAP am-and cervical paraspinal muscles were also tested andplitude and strength as measured by maximum volun-showed severe denervation. Spontaneous activity wastary isometric contraction are strongly correlated inpresent in the diaphragm in 5 out of 6 patients tested. ALS patients.10 The phrenic distal motor latencies inMotor unit recruitment was variably reduced in limb our patients were normal or only mildly prolonged.

muscles. In the diaphragm, motor unit recruitment This is similar to the findings in phrenic nerve con-was either absent or severely reduced to a few rapidly duction studies in ALS patients with respiratory symp-firing motor units. toms6 and in limb nerves in ALS patients.4 Thus,

the diaphragmatic CMAP amplitude appears to be aDISCUSSION more sensitive measure of diaphragmatic functionElectrophysiological studies in all our cases demon- than the distal latency in patients with ALS, althoughstrated evidence of denervation and reinnervation in some authors6,14 considered diaphragmatic CMAPthree or more extremities with normal sensory amplitude unreliable.

Table 1. Results of needle electromyography.

First dorsal Vastus Tibialis ExternalEMG findings Biceps interosseous medialis anterior oblique Diaphragm

Case 1Fibrillation 11 21 0 11 31 11

Fasciculation 11 0 0 11 0 0Recruitment QQ QQQ Q QQ QQQ No units

Case 2Fibrillation 11 Not tested 21 31 0 11

Fasciculation 0 Not tested 11 0 0 11

Recruitment QQ Not tested QQ Normal Normal QQQCase 3

Fibrillation 11 21 11 21 Not tested 11

Fasciculation 0 11 11 0 Not tested 0Recruitment Normal Q Normal Q Not tested QQQ

Case 4Fibrillation 11 21 21 Not tested 11 11

Fasciculation 11 0 0 Not tested 11 0Recruitment Q QQ QQ Not tested QQ QQQ

Case 5Fibrillation 21 0 21 21 Not tested Not testedFasciculation 0 0 0 0 Not tested Not testedRecruitment Normal QQ Normal Normal Not tested Not tested

Case 6Fibrillation 11 11 11 21 0 0Fasciculation 0 0 0 0 0 0Recruitment Q Q Q Q Normal No units

Case 7Fibrillation 11 21 11 21 21 21

Fasciculation 11 11 11 11 11 0Recruitment Q QQ QQ QQ QQQ QQQ

0, none; 11, 21, 31, 5 few, moderate, abundant; Q, QQ, QQQ, mildly, moderately, markedly decreased.

518 Short Reports MUSCLE & NERVE April 1997

Needle EMG was useful in demonstrating dener- ment decisions by the treating physicians, patients,and their family.vation of the diaphragm. Compared with limb mus-

cles, it is more difficult to demonstrate spontaneousactivity in the diaphragm, because it can only be

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CF: Neuromuscular disorders associated with failure to weancauses of respiratory failure were severe degenerationfrom the ventilator. Intensive Care Med 1995;21:737–743.of phrenic motoneurons and denervation of the dia-

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Such information was crucial in subsequent manage-

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