Page 6 P H Y S I O T H E R A P Y Marth, 1961 Electromyography Some M edical articles summarized by V A L E R IE R U D O L P H B.Sc. (Physiotherapy) R and. El e c t r o m y o g r a p h y is one o f several m ethods o f electrodiagnosis the purpose o f which is to establish the presence and sometimes the cause o f paralysis o f muscles. A lthough, a t the m om ent, it is carried o u t by doctors and n o t by physiotherapists, it is im p ortant fo r therapists to understand the principles on which it is based. It is unlikely to replace o u r Strength-duration tests but it form s a useful complement to them . T he two m ethods are used both to diagnose and to give some idea o f the prognosis, in cases o f paralysis o r muscle weakness. Electrodiagnosis is done either by:— 1. A pplying electrical stimuli o f different durations and forms to a muscle and assessing the current o r voltage needed to produce a m inim al contraction, and also by studying the type o f muscle contraction, and from the results, draw ing a conclusion as to the degree o f degeneration present, o r by:— 2. R ecording o r studying the varying electrical potentials in a muscle fibre o r m otor unit. Reaction of Degeneration This is the altered response to an electrical stimulus applied to muscle with an impaired nerve supply. It varies in severity depending on the am ount o f dam age to the nerve. T here may be:— I. Complete Reaction o f Degeneration This occurs when the nerve is destroyed and the muscle physiologically isolated from the controlling centres in the central nervous system. II. Partial Reaction o f Degeneration This occurs when there is partial interruption o f the peripheral nerve; th at is, between the anterior horn cell and the m otor end plate. Some axons are destroyed and others rem ain intact. T he term “ P artial R eaction o f D egeneration” has a wide span ranging from alm ost complete destruction to near norm ality, so n o definite signs can be laid dow n as being representative o f it. I t is merely the long interm ediate stage between the tw o extremes. Methods of Electrodiagnosis I. Testing fo r Reaction o f Degeneration This m ay be done by:— (a) T he G alvanic-Faradic test or (b) The S trength-duration test or V oltage-duration test in which (1) Square-wave impulses o f varying d uration o r additionally (2) Progressive impulses o f varying duration are applied to a muscle. II. Recording the Electrical Potentials o f the Muscle T he contraction o f a muscle fibre is accom panied by a change in the electrical potential which can be measured, amplified and recorded. T he process by which this is done is Electrom yography. The technique investigates the activity o f single m o to r units, which consist o f:— (1) A n anterior h o rn cell. (2) T he axon derived from it. (3) T he muscle fibres innervated by it. or o f a single muscle fibre. It differs from the two m ethods m entioned previously as these test the muscle as a whole. Apparatus used in Electromyography I. Electrodes F o r accuracy, needle electrodes m ust be used, as this is| the only means o f recording the activity o f individual muscle fibres. T he two poles are obtained by:— (a) A piece o f wire (the active electrode) placed inside a hypoderm ic needle (the indifferent) or (b) A solid needle, insulated except at the tip, forming the active electrode, with the indifferent electrode on the surface. II. Recording Devices T he electrical activity o f a m otor unit or a muscle fibre is picked up by the above-m entioned electrodes, considerably amplified (from m icrovolts to 60-100 volts) and then fed into a C athode R ay Oscilloscope. T his consists o f a cathode ray tube which includes the following essentials:— A n evacuated glass tube containing:— (a) A heated cathode to produce electrons. (b) Several anodal plates which accelerate and focus the beam o f electrons on to (c) A fluorescent screen where the focussed beam of electrons appears as a lum inous spot. Between the cathode and the anodal plates (d) A negatively charged grid to control the total electron flow. Since wave form s have to be seen on the screen, it m ust be possible to move the beam o f electrons in any direction on the screen. T his is done by (e) T w o sets o f deflector plates which are placed betw een' the last anode and the screen. The two sets o f plates are at right-angles to each other. O ne set, usually called the X plates, causes horizontal deflection o f the electron beam. T he other set o f plates, usually called the Y plates, produces vertical m ovem ent o f the lum inous spot. T o produce a wave-form, a time base circuit m ust be incorporated. T his is connected to the X plates o f the tube. T he time base unit m ust be synchronized to the frequency of the wave form to be examined. T his controlled, synchronized horizontal m ovem ent o f the electron beams is the so-called “ sweep.” Vertical deflection o f the electron beam is produced by the potential o f the electron wave which causes the spot to move up and dow n the screen. In this way, the electrical potential can be:— (1) Seen on the fluorescent screen. (2) Perm anently recorded on a camera. (3) Fed into a loud-speaker. T he character o f the sound gives an indication of the am plitude and duration o f the wave form. (4) R ecorded by a pen-writer. A lthough this is n o t completely accurate owing to ted inertia o f the pen, it is im portant because it can be studihe R ep ro du ce d by S ab in et G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r (d at ed 2 01 3. ) , after the needles have been removed from the a t • t’c muscles Also, exact measurem ents can be taken ^ ‘ comparisons m ade with the norm al. M ethod used to record the potentials After the adm inistration o f a local anaesthetic, a needle • inserted into the muscle and is moved from one fibre to , S r the potentials o f each being viewed on the screen a n d w o r d e d by one of the devices described above. Types of Response seen in Electromyography I Action Potential ' ' The contraction o f a single muscle fibre is triggered off at rr,fltor end plate and is accom panied by a wave o f nega- M tv which travels along the muscle fibres. T h is wave form can be picked up by the tw o electrodes nlaced close together in the muscle fibre and will result in a Hinhasic wave i.e. the action potential. (G raph 1). N o r m a lly the whole m otor unit “ fires” i.e. m any muscle fibres contract with the result th a t the am plitude is higher and the duration longer. (G raph 2.) March, 1961 P H Y S I O T H E R A P Y Page 7 G raph 1 G raph 2 II. Denervation Potential Rhythmic twitching o f individual muscle fibres causes a series o f short, rapid waves seen on the screen as denerva­ tion fibrillation. I I I . Fasciculation Voltages These are spontaneous, involuntary contractions o f a group o f muscle fibres. They are sometimes seen by the naked eye as a twitching o f the muscle and m ay be a norm al phenomenon, as in fatigue. However, it usually indicates some pathology and may be o f tw o types:— (1) A slow twitch at intervals o f 10-20 seconds indicating a m otor neuron disease such as progressive muscular atrophy. (2) A fast, rhythm ic fasciculation m ay be seen in the paretic muscles in poliomyelitis, neuritis and G uillain- Barre syndrome. It may be due to irritation o f the nerve, p ain, o r tension due to fatigue and weakness. Experience is needed to differentiate between the various types and to decide on the cause. IV. Synchronized M otor Unit Potentials These may be norm al but are often a sign o f pathology They occur in the following circum stances:— (1) When a norm al muscle is fatigued. (2) When a norm al muscle is w orking against maximum resistance. (3) In a weakened or partially paralysed muscle. Usually, when a muscle contracts, some o f the fibres contract out o f time with the others to produce a sm ooth contraction and delay fatigue. In the three cases mentioned above, the sm oothness o f the m ovem ent is forfeited in favour o f obtaining m axim um power. T he result is a simultaneous contraction o f all fibres, giving rise to synchro­ nous m otor unit potentials. V. Complex M otor Unit Voltages These are polyphasic potentials usually dem onstrating five or more peaks. They are often seen in the recovery phase following a nerve lesion and so m ay be o f prognostic value. Specific Responses in Electromyography I. In Normal M uscle (a) A t Rest. There are n o voltages generated i.e. a norm al muscle at rest is electrically silent. This hygienic Physiotherapist Uniform has so many good points! Sa nfo rise d, M e rc e rise d w h ite tw ill A d ju sta b le n e c klin e — to the specification o f the U n iv e rs it y P h y sio th e ra p y Section B re a st p o c k e t - * - " '* L o n g sleeves - D e ta cha b le belt • T w o h ip pocke ts, o n e w ith c o n ce a le d inside p o c k e t .. . B u tto n fro n t .. DELILAH GARMENT O F Q U A L IT Y AN D STYLE by T H E HOUSE OF E N S I GN M a n u f a c tu r e d by The AFRICAN CLO THIN G F A C TO R Y td. P.O. BOX 1098 CAPE TOW N a n d o b ta in a b le f r o m good c lo th in g sto re s e v e r y w h e r e R ep ro du ce d by S ab in et G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r (d at ed 2 01 3. ) Page 8 P H Y S I O T H E R A P Y March, 1961 N orm al Complete Electrical Silence D U R I N G N orm al Simple M otor U nit Voltages A T R E S T D enervated Fibrillation Voltages V O L U N T A R Y D enervated Partially D enervated Fibrillation $ or Fascicu­ lation Voltages E F F O R T Partially D enervated Fibrillation Voltages Simple 4 or Complex M otor U nit Voltages N am e o f wave M agnitude o f wave in microvolts D u ratio n of wave in milliseconds Frequency o f wave per second A udio-sound D iagnostic significance Simple m o to r unit voltages occurring d u r i n g v o l u n t a r y effort. 100-2000 2-10 5-60 L O W - p i t c h e d t h u m p i n g sound. N orm al muscular contraction. Fibrillation voltages a t rest. 10-100 1-2 2-30 H i g h - p i t c h e d click. A b n o r m a l w a v e signifying dennerva- tion. Fasciculation a t rest. 20-1000 5-15 Irregular incon­ s t a n t r e p e t i ­ tio n frequency. H a r s h , lo w - p i t c h e d n o i s e A b n o r m a l w a v e associated w ith de­ generation or irrita­ tion. Complex m otor unit voltages during volun­ tary effort. 20-1200 5-20 5-30 H a r s h , l o w - p i t c h e d n o i s e A b n o r m a l w a v e associated w ith de- g e n e r a t i o n o r regeneration. Base-line disturbances d u r i n g v o l u n t a r y effort. 5-500 5-30 2-30 D i s t a n t s o f t indistinct ru m ­ bling sound. A b n o r m a l w a v e associated w ith early regeneration o r late degeneration. R ep ro du ce d by S ab in et G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r (d at ed 2 01 3. ) (b> ^ g r e ^ e ^ c t f o n ^ p o t e n t i a l s or simple m otor unit voltages. . . n „ Qtrone Contraction. T he P o te n tia ls have several spikes i.e. They are poly-phasic. . , The other factors (param eters) which give a n indication of the c o n d itio n s are: m V o lta g e : 100-2,000 microvolts. ™ D u r a tio n : 2-10 milliseconds. m F r e q u e n c y : 5-60 p e r s e c o n d . (4) S o u n d : A lo w , thum ping sound. I I In a Complete Reaction o f Degeneration rv n erv atio n fibrillation is seen at rest and on attem pted mnwrnent As com pared w ith the action potentials, the p a r a m e t e r s o f the fibrillations are as follows : - m Voltage: 5-100 microvolts. (2) D u r a t i o n : 1—2 m illis e c o n d s . H) Frequency: 2-30 per second. (4) Sound: A high-pitched click. III. In a Partial Reaction o f Degeneration ^ S o m e 'fibres are electrically silent and others show fibrillations. T he higher the num ber o f fibres showing fibrillations, the m ore severe the paralysis. (b) On Movement. On voluntary o r reflex contraction, there are simple or complex m oto r unit voltages. SUMMARY Functions o f Electromyography (1) T o ascertain w hether action potentials exist in a given muscle. March, 1961 P H Y S I O T H E R A P Y Page 9 (2) T o ascertain w hether they are norm al o r abnorm al. (3) T o ascertain the type and probable cause o f the abnorm ality. Diagnostic Criteria T he criteria to be examined a r e :— (1) T he presence o r absence o f potentials when the muscle is at rest. (2) T he presence or absence o f potentials during volun­ tary effort. (3) T h e norm al o r abnorm al characteristics o f these potentials. A ny abnorm al characteristics m ust then be interpreted and com pared w ith the norm al patterns. E lectrom yography constitutes one o f the few completely objective means o f diagnosis o f neurological com plaints because it is impossible for the p atient to control the presence o r absence o f fibrillations and o th er abnorm al phenom ena. They can only occur when there is im pairm ent o f the nerve supply o r som e genuine nervous pathology. In conjunction w ith the S trength-duration m ethod o f muscle testing, it constitutes a reliable m eans o f diagnosis and the findings m ay also be o f prognostic value. Acknowledgement I would like to acknowledge the help given m e by M iss M . H inz, lecturer in Electrotherapy, Witwatersrand University. References Electrodiagnosis and Electrotherapy, edited by Sidney Licht. Archives o f Physical M edicine:— August 1949. J. Golseth and O. Huddlestone. September, 1950. G. Hirschberg and A. Abramson. THE BIRTCHER MEGASON VI ULTRASONIC UNIT To the more than 20,000 physicians now using ultra­ sonic therapy in the treatm ent of a host of acute and chronic conditions, this precision instrum ent adds new dimensions of accuracy and treatm ent ease. Descriptives and medical journal reprints on request. A NEW CONCEPT IN TREATMENT T f f g f f e c f l f P ( 4 ^ ( ^ l i l i w L l P T Y ) l t d “ Cape York” , 252 Jeppe St., Johannesburg P.O. Box 3378 • Telephone 23-8106 and at President House, 20 Barrack Street, Cape Town. P.O. Box 195. Telephone 41-1172 R ep ro du ce d by S ab in et G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r (d at ed 2 01 3. )