The exercise test in periodic paralysis

Of 21 patients with clinically definite hypokalemic, hyperkalemic, or normokalemic periodic paralysis, 15 (71%) had a greater than normal increase in compound muscle action potential amplitude during 2-5 minutes of intermittent strong voluntary contraction of the muscle. This increase was followed by a progressive decline in amplitude, which was greater than in a control population and which was most rapid during the first 20 minutes after exercise. The amplitude often decreased to a level below the preexercise level. A similar response was seen in six of nine patients with periodic paralysis secondary to disorders such as thyrotoxicosis. This test may have value in the identification of patients with periodic paralysis.     

Improvement of the exercise test after therapy in thyrotoxic periodic paralysis

The diagnosis of periodic paralysis (PP) can be aided by demonstrating a decrease in compound motor action potential (CMAP) amplitude after several minutes of exercise. We report a case of secondary hypokalemic PP due to thyrotoxicosis in which the decrease in the CMAP amplitude after exercise dramatically improved after treatment, when a euthyroid state was achieved. The exercise test is a useful electropghysiologic means of monitoring the neuromuscular status of patients with thyrotoxic periodic paralysis prior to, and after treatment of the thyrotoxicosis.     

Relationships between the changes in compound muscle action potentials and selective injuries to the spinal cord and spinal nerve roots.

OBJECTIVE: Compound muscle action potentials (CMAPs) evoked by transcranial electrical stimulation have been widely introduced to monitor motor function during spinal surgery. They may reflect segmental injuries as well as injuries to motor-related tracts in the spinal cord. However, we have experience with some patients who developed postoperative segmental motor weakness without any potential changes during surgery. To evaluate the efficacy of this method, we used a cat model to observe the relationships between potential changes and selective injuries to the white and gray matters of the spinal cord and spinal nerve roots. METHODS: Ten CMAPs were obtained before and after injury to the spinal cord and spinal nerve roots in 20 cats. Changes in the amplitude, latency, and duration of CMAPs were analyzed. RESULTS: CMAPs decreased in amplitude significantly after the insult to the motor-related tracts in the spinal cord in all cats, while the potentials did not always change when the insult was restricted to a limited area in the anterior horn of the spinal cord or to the single spinal nerve root. CONCLUSIONS: CMAPs may not exactly reflect segmental injury, and careful attention should be paid to the interpretation of CMAPs.     

A case of hypokalemic periodic paralysis: utility of exercise test for the assessment of therapeutic efficacy]

We report a 14-year-old male with hypokalemic periodic paralysis. He noticed periodic paralysis at the age of 11. Any complication did not accompany the symptom. At the age of 12, hypokalemia was found during an episode of paralysis, and he was diagnosed as hypokalemic periodic paralysis. The frequency of paralytic attack increased around April 2000. Although long-acting oral potassium (32 mEq/day) was administered, it did not give favorable effect. Therapeutic spironolactone trial also failed. After the reconfirmation of the diagnosis of periodic paralysis by an exercise test, oral acetazolamide (750 mg/day) was started. In subsequent exercise test, the increment of the CMAP amplitude of abductor digiti minimi during exercise became smaller and the decrement of CMAP amplitude after exercise disappeared thereafter, which was assumed to be related with clinical improvement. The noninvasive exercise test is useful not only to diagnose periodic paralysis but also to evaluate therapeutic efficacy.     

The role of the intact hemisphere in recovery of midline muscles after recent monohemispheric stroke

Transcranial magnetic stimulation (TMS) of the motor cortex was used to study basic mechanisms of motor reorganization after major hemispheric stroke in humans. We sought to clarify the possible role of the intact hemisphere in motor recovery of the lingual muscles, and to evaluate the compensatory use of preexisting uncrossed motor pathways projecting to these midline muscles. TMS and bilateral surface recordings from the lingual muscles were carried out in six selected stroke patients who presented with a unilateral lingual paralysis after a limited monohemispheric ischemia. The first examination was performed during the symptomatic stage (t ₁) and was repeated after complete recovery of lingual function had been established (t ₂). The cortical motor output patterns were analyzed and compared with the data from 40 healthy controls. In the controls TMS of either hemisphere invariably produced contralateral and ipsilateral compound muscle action potentials (CMAPs), elicited through crossed and uncrossed central motor pathways, respectively. In most individuals an asymmetric cortical motor output pattern was found, as significantly greater mean CMAPs of shorter onset latencies were recorded from the contralateral lingual muscles than from the ipsilateral responses. In the six patients with a unilateral lingual paralysis a similar pattern was found on initial examination by stimulating the intact hemisphere, whereas TMS of the affected hemisphere failed to elicit any CMAP bilaterally. At t ₂ all patients had regained normal lingual function. Only one patient showed evidence of a complete recovery of the primarily affected hemisphere, as TMS now elicited normal CMAPs bilaterally. In the remaining five patients the unilateral interruption of the corticonuclear pathways persisted in spite of complete functional recovery. In these subjects the recovery of symmetric lingual movements must be attributed to the intact hemisphere. From this it is concluded that recovery of a unilateral lingual paralysis after restricted monohemispheric lesions is possible without recovery of the cortical motor projections from the affected hemisphere. In these cases the intact hemisphere is responsible for restoration of normal lingual movements, most likely by potentiating the effect of preexisting uncrossed motor pathways. Received: 26 March 1998 Accepted: 24 June 1998     

低钾型周期性瘫痪患者运动诱发试验中肌力和肌电图改变与血钾的关系

目的 通过长时运动诱发试验,观察低钾型周期性瘫痪患者肌力和肌电图的变化与血钾之间的关系.方法 收集确诊为低钾型周期性瘫痪患者78例,对小指展肌进行运动诱发试验测定,以拇短展肌作为对照,观察120 min,测定运动诱发前后尺神经/小指展肌和正中神经/拇短展肌复合肌肉动作电位(compound muscle action potential,CMAP)波幅变化,同时观察患者小指外展和小指内收肌力以及拇短展肌肌力的变化,部分患者测定运动前后血钾水平.分析运动后不同肌肉的肌力、CMAP波幅与血钾之间的关系.结果 在小指外展运动后,78例患者尺神经CMAP波幅运动后比运动前明显下降,分别为(4.6±2.7)、(9.6±3.2)mV(t=16.047,P=0.000),而正中神经CMAP波幅在小指外展运动后与运动前相比无明显差异,分别为(10.9±4.2)、(11.2±3.9)mV(t=0.673,P=0.822).在运动后,76例小指外展肌力下降;有41例小指外展肌力小于Ⅲ级,但同侧小指内收和拇短展肌肌力仍为V级,对其中10例患者在运动前和运动后测定血钾,结果无明显差异,分别为(3.8±0.3)、(3.9±0.4)mmol/L(t =0.395,P=0.702).结论 在低钾型周期性瘫痪患者进行运动诱发试验时,血钾并非影响肌力和CMAP波幅变化的关键因素.     

An unusual presentation of hypokalemic paralysis with evolving pure motor hemiparesis

Pure motor hemiparesis is a vascular syndrome that is occasionally mimicked by central or spinal pathologies. However, metabolic neuromuscular disorders have not been reported to mimic this condition. We present a 52-year-old male patient with hypokalemic paralysis who presented with the early symptoms of acute-onset pure motor hemiparesis. Neurological examinations revealed right-sided weakness without bulbar, extraocular, or respiratory involvement. Ischemic stroke was initially diagnosed on the basis of the acute-onset unilateral motor deficit and the patient’s history of hypertension, stroke, and previous cerebral infarctions. The right hemiparesis and weakness of the left limbs worsened on the day after admission. The patient’s weakness rapidly reversed after correction of hypokalemia, and a diagnosis of hypokalemic paralysis was finally established. This unusual hemineurological presentation should alert medical personnel to the possibility of reversible metabolic neuromuscular disorders, thereby avoiding delayed diagnosis.     

Ankle position and voluntary contraction alter maximal M waves in soleus and tibialis anterior

Compound muscle action potentials (CMAPs) recorded using surface electrodes are often used to assess the excitability of neural pathways to skeletal muscle. However, the amplitude of CMAPs can be influenced by changes at the recording site, independent of mechanisms within the central nervous system. We quantified how joint angle and background contraction influenced CMAP amplitude. In seven subjects CMAPs evoked by supramaximal transcutaneous electrical stimulation of motor axons (M(max)) were recorded using surface electrodes from soleus and tibialis anterior (TA) at static positions over the full range of ankle movement at 5 degrees intervals. Across subjects the peak-to-peak amplitude of M(max) was 155% and 159% larger at the shortest than longest muscle lengths for soleus and TA, respectively. In five subjects the effect of ankle position and voluntary contraction on M-wave/H-reflex recruitment curves was assessed in the soleus. Both ankle position and level of contraction significantly influenced M(max), H(max), and the H(max) to M(max) ratio, but there were no interactions between the two parameters. These peripheral changes that influence M(max) will also impact other CMAPs such as submaximal M-waves, H-reflexes, and responses to transcranial magnetic stimulation. As such, during experimental studies CMAPs evoked at a given joint angle and contraction level should be normalized to M(max) recorded at similar joint angle and contraction strength.     

Comparison of motor conduction abnormalities in lumbosacral radiculopathy and axonal polyneuropathy.

We compared the frequencies and types of motor conduction abnormalities found in peroneal and tibial nerves of patients with either L5/S1 radiculopathies (n = 47) or axonal polyneuropathies (n = 49). In axonal neuropathies, compound muscle action potentials (CMAPs) were more likely to be either unobtainable or, if present, of low amplitude, prolonged in distal latency or both. F responses were more often absent, impersistent, or prolonged in minimal latency. In contrast, CMAPs in lumbosacral radiculopathies were more likely to be normal in both amplitude and distal latency. The most frequent F-response abnormality in radiculopathies was a prolonged maximum-minimum latency range rather than abnormalities of minimal latency or persistence. Logistic regression analysis demonstrated that different patterns of motor conduction abnormalities result from lumbosacral radiculopathy and distal axonopathies. The model was able to correctly classify disease state in 76% of subjects with a sensitivity of 74% and specificity of 80%.     

Focal magnetic coil stimulation reveals motor cortical system reorganized in humans after traumatic quadriplegia

A figure of ‘8’ magnetic coil (MC) was used to stimulate focally the motor cortex of two adult, traumatic quadriplegics and three normal adults. The two patients were injured approximately 2 years previously and had intensive physiotherapy, including biofeedback training of biceps and deltoid muscles, respectively, which were the most caudal muscle spared. The focal MC elicited compound motor action potentials (CMAPs) from these muscles from a much wider area of scalp than in the normal subjects. Latency of biceps and deltoid CMAPs were inversely related to CMAP amplitude. A reorganization of the motor cortical projection system is inferred, in which areas normally eliciting digit movements instead activate muscles in quadriplegics just above the spinal level. The reorganization applies also to the central sense of movement normally elicited by focal frontal cortex stimulation. Possible mechanisms of the reorganization and an implication for rehabilitation are discussed.     

Enhancement of K+ conductance improves in vitro the contraction force of skeletal muscle in hypokalemic periodic paralysis

An abnormal ratio between Na+ and K+ conductances seems to be the cause for the depolarization and paralysis of skeletal muscle in primary hypokalemic periodic paralysis. Recently we have shown that the "K+ channel opener" cromakalim hyperpolarizes mammalian skeletal muscle fibers. Now we have studied the effects of this drug on the twitch force of muscle biopsies from normal and diseased human skeletal muscle. Cromakalim had little effect on the twitch force of normal muscle whereas it strongly improved the contraction force of fibers from patients suffering from hypokalemic periodic paralysis. Recordings of intracellular K+ and Cl- activities in human muscle and isolated rat soleus muscle support the view that cromakalim enhances the membrane K+ conductance (gK+). These data indicate that "K+ channel openers" may have a beneficial effect in primary hypokalemic periodic paralysis.     

Erythrocyte membrane studies in familial hypokalemic periodic paralysis.

A study of RBC membrane functions was performed in four patients suffering from familial hypokalemic periodic paralysis who had permanent muscular weakness. Electrophoretograms of membrane proteins, cell deformability, calcium-promoted potassium efflux, calcium-ATPase activity, and endogeneous phosphorylation of membrane proteins were all within the normal range. These results are compared with similar studies performed in myotonic and Duchenne-type dystrophies, in which abnormalities in the RBC membrane have been described. The results do not support the theory of RBC involvement in hypokalemic periodic paralysis. However, this does not imply that the muscle cell membrane is not involved in the underlying pathological processes in this disorder.     

Exercise and rest in hyperkalemic periodic paralysis

The effect of muscle immobility, with and without prior vigorous exercise, on amplitude and area of the compound muscle action potential (CMAP) to supramaximal nerve stimulation was studied in a family with hyperkalemic periodic paralysis. Amplitude and area of different CMAPs were measured during basal state, sustained immobility, and after brief maximal voluntary exercise of these muscles. Sustained immobility reduced the amplitude and area of the CMAP, with maximal effect occurring after 30 minutes. Though brief intense exercise seemed to minimally accentuate these effects of subsequent immobility at certain times, serial CMAP monitoring over 60 minutes did not reveal major differences between exercised and nonexercised muscles. Muscle immobility in itself can alter the CMAP in hyperkalemic periodic paralysis. Prior intense muscle exercise may accentuate this to some degree. This appears to be the electrophysiologic correlate of the characteristic symptom of focal weakness induced by rest after exercise.     

Influence of posture and voluntary background contraction upon compound muscle action potentials from anterior tibial and soleus muscle following transcranial magnetic stimulation.

Compound muscle action potentials (CMAPs) were recorded from anterior tibial (TA) and soleus (SOL) muscles following transcranial magnetic stimulation of motor cortex in 10 healthy subjects: (1) while standing upright without support, (2) while sitting, and (3) while lying supine. The results of this study demonstrate a significant influence of posture upon the amplitudes of CMAPs. Postural facilitation presented itself, firstly, in terms of a higher incidence of bilateral activation of distal leg muscles during stance and, secondly, as significant enhancement of the amplitude of CMAPs while standing as compared to lying supine. The onset latency, however, did not disclose a significant shortening during stance. To assess the effects of preinnervation subjects voluntarily adjusted the level of TA activity to 5%, 10% and 20% of maximum isometric force respectively before cortex stimulation. Voluntary background contraction resulted in a significant increase of amplitude of CMAPs but, in contrast to postural facilitation, concomitant with a significant decrease in onset latency. These results point to a somewhat different mechanism of facilitation during stance as compared to voluntary preinnervation. But it cannot be decided whether cortical mechanisms, different descending systems, the spinal circuitry or a combination of these factors is responsible for the observed effects.     

Motor evoked potentials in unilateral lingual paralysis after monohemispheric ischaemia

OBJECTIVES—The occurrence of a lingual paralysisafter unilateral upper motor neuron lesions is an infrequent clinicalphenomenon, and the underlying pathophysiological mechanisms are poorlyunderstood. We studied the cortical motor representations ofipsilateral and contralateral lingual muscles in healthy controls andin a selected group of stroke patients, to clarify the variableoccurrence of a lingual paralysis after recent monohemispheric ischaemia.
METHODS—A special bipolar surface electrode wasused to record the ipsilateral and contralateral compound muscle actionpotentials (CMAPs) from the lingual muscles after transcranial magneticstimulation (TMS) of the human motor cortex and peripheralelectrical stimulation (PES) of the hypoglossal nerve medial to theangle of the jaw. Four patients with a lingual paralysis (group 1) andfour patients with symmetric lingual movements (group 2) aftermonohemispheric first ever stroke were studied and compared with 40 healthy controls.
RESULTS—In controls, TMS of eitherhemisphere invariably produces CAMPs in the ipsilateral andcontralateral lingual muscles, elicited through crossed anduncrossed central motor pathways, respectively. In the 40 healthy controls, TMS of either hemisphere elicited CMAPs ofsignificantly greater amplitudes and shorter onset latencies from thecontralateral muscles compared with the ipsilateral responses (p<0.0001). In the patient groups, TMS of the affected hemisphere failed to evoke any CMAP from either lingual side; TMS of the unseveredhemisphere always produced normal ipsilateral and contralateral responses, irrespective of whether the ipsilateral muscles were paralysed or not.
CONCLUSIONS—Bilateral crossed and uncrossedcorticonuclear projections are invariably existent in humans. Afterunilateral interruption of these pathways, some people do exhibit alingual paralysis whereas others do not. The development of a centrallingual paralysis is most likely dependent on the ability of theunsevered hemisphere to utilise the pre-existent uncrossed motorprojections. The variable availability of these pathways amongindividual subjects is in good agreement with the inconstant occurrenceof a lingual paralysis after restricted monohemispheric lesions.

     

Proximal and segmental motor nerve conduction in the sciatic nerve produced by percutaneous high voltage electrical stimulation

Percutaneous high voltage electrical stimulation was applied to the proximal sciatic nerve at the hip in 18 normal subjects to evaluate motor conduction in the proximal sciatic nerve, and short-segment stimulation of the sciatic and posterior tibial nerves was given in 6 normal subjects. Compound muscle action potentials (CMAPs) were recorded from the abductor hallucis (AH) and extensor digitorum brevis (EDB) muscles. Supramaximal stimulation was easily obtained at the proximal sciatic nerve and all the sites in the short-segment stimulation. The motor nerve conduction velocity of the sciatic nerve between the hip and the popliteal fossa was 49.2 ± 4.24 m/sec in the tibial division and 54.1 ± 6.48 m/sec in the peroneal division. The respective peak-to-peak amplitude and negative-peak areas of the CMAPs at the hip were reduced to 86.8 ± 5.65% and 97.3 ± 5.36% for the tibial division, and 93.4 ± 7.06% and 96.8 ± 5.09% for the peroneal division as compared to the values for the popliteal fossa. The negative-peak duration of the CMAPs at the hip point were increased to 109.2 ± 7.2% for the tibial nerve and 107.1 ± 5.68% for the peroneal nerve as compared with the duration at the popliteal fossa. This method is non-invasive and useful for evaluating motor nerve conduction in the lower limb.     

亚临床甲亢并周期性瘫痪的临床分析

目的 分析亚临床甲亢并周期性瘫痪的临床特点.方法 测定总T3、总T4、游离T3、游离T4、促甲状腺素,并回顾分析8例亚临床甲亢并周期性瘫痪的临床资料.结果 青壮年男性发病,低钾型周期性瘫痪为主要临床表现,无明显甲状腺功能亢进症表现,测定总T3、总T4、游离T3、游离T4正常,促甲状腺素下降,补钾治疗有效.结论 青壮年男性亚临床甲亢的主要临床特点是低钾型周期性瘫痪.     

Axonal hyperpolarization associated with acute hypokalemia: multiple excitability measurements as indicators of the membrane potential of human axons

Multiple nerve excitability measurements have been proposed for clinical testing of nerve function, and an important determinant of excitability is membrane potential. We report a patient with acquired hypokalemic paralysis in whom multiple excitability indices (stimulus-response curve, strength-duration properties, threshold electrotonus, recovery cycle) were measured during and after an acute hypokalemic attack (serum K(+) level, 2.1 mEq/L and 4.5 mEq/L, respectively). During hypokalemia, there was a shift of the stimulus-response curve to the right, a decrease in strength-duration time constant, a "fanning-out" of responses during threshold electrotonus, a reduction in relative refractory period, and an increase in superexcitability; all of these indicate axonal hyperpolarization, presumably due to the K(+) equilibrium potential being more negative. These indices returned to normal 20 h later, associated with normalization of the serum K(+) level. These results demonstrate that the changes associated with hypokalemic paralysis are not confined to muscle and that axons undergo hyperpolarization in vivo. Multiple excitability measurements can be used as a tool to identify changes in membrane potential of human axons.     

Electrophysiologic findings and grip strength after nerve injuries in the rat forelimb

We developed electrophysiologic methods for testing the three major forelimb nerves as a tool to evaluate motor and sensory recovery in rats. Median, ulnar, or radial nerves were transected and repaired in Sprague-Dawley rats. Compound muscle action potentials (CMAPs) and somatosensory evoked potentials (SSEPs) were recorded preoperatively and at various postoperative intervals. Correlation between grip strength and CMAPs was investigated. Reliable CMAPs were recorded for all three nerves. Median- or ulnar-nerve-derived SSEPs were reliably recorded; radial SSEPs could not be recorded. CMAPs followed typical regeneration patterns after nerve repair. SSEPs showed a consistent peak latency but fluctuating amplitude. Grip strength and median CMAP amplitude correlated positively. We conclude that it is possible to conduct minimally invasive electrophysiologic testing in rat forelimbs. The CMAP is a valid parameter that shows the typical time course of nerve regeneration and reinnervation.     

Magnetic lumbosacral motor root stimulation with a flat,large round coil

ObjectiveThe aim of this paper is to develop a reliable method for supramaximal magnetic spinal motor root stimulation (MRS) for lower limb muscles using a specially devised coil.MethodsFor this study, 42 healthy subjects were recruited. A 20-cm diameter coil designated as a Magnetic Augmented Translumbosacral Stimulation (MATS) coil was used. Compound muscle action potentials (CMAPs) were recorded from the abductor hallucis muscle. Their CMAPs were compared with those obtained by MRS using a conventional round or double coil and with those obtained using high-voltage electrical stimulation.ResultsThe MATS coil evoked CMAPs to supramaximal stimulation in 80 of 84 muscles, although round and double coils elicited supramaximal CMAPs in only 15 and 18 of 84 muscles, respectively. The CMAP size to the MATS coil stimulation was the same as that to high-voltage electrical motor root stimulation.ConclusionsMATS coil achieved supramaximal stimulation of the lumbosacral spinal nerves.SignificanceThe CMAPs to supramaximal stimulation are necessary for measurement of the amplitude and area for the detection of conduction blocks. The MATS coil stimulation of lumbosacral motor roots is a reliable method for measuring the CMAP size from lower limb muscles in spinal motor root stimulation.