OFPAIN AND PARAESTHESIAE BY NERVE BLOCK LESION · those of pain and painful pins and needles; when it affects the posterior columns of the cord, the sensation is one of painless pins

RELIEF OF PAIN AND PARAESTHESIAE BY NERVEBLOCK DISTAL TO A LESION

BY

R. F. KIBLER* and P. W. NATHANFrom the Neurological Research Unit of the Medical Research Council, the National Hospital, Quieen Square,

London, W. C.l

Lesions of afferent pathways may give rise to avariety of spontaneous sensations. When a lesionaffects nerves, nerve roots, the root entry zone,or the spino-thalamic tract, the sensations are usuallythose of pain and painful pins and needles; whenit affects the posterior columns of the cord, thesensation is one of painless pins and needles or oftingling. It is natural to think that the pain andparaesthesiae are due to the discharge of nervefibres in or near the lesion, and that the lesion onthe afferent pathway causes these nerve fibres to fireoff.

In this paper, evidence will be presented to showthat local anaesthetic injections of the afferentpathway, distal to the site of the lesion, may stopthe pain or paraesthesiae; further, that this effectmay far outlast the duration of the anaesthesia;and further, that blocking a peripheral nerve supply-ing a large part but not the whole of the regionwhere the pain or paraesthesiae are felt may removethese sensations from the entire region.A summary of the cases in which a nerve block

distal to the lesion gave these results is presentedas Table I. The cases are now briefly described andthe experimental protocols are given.

ResultsN.T. (National Hospital No. 80434.)-This 42-year-

old woman was admitted to the National Hospital inNovember, 1958. In January, 1955, she had first noticeda cramping feeling and pins and needles in the righthand, extending up the outer aspect of the forearm andarm. Within one month of the onset of these para-esthesiae, moderate weakness of the limb developed.She was treated by traction of the neck and ordered towear a sling. The strength of the limb returned to normalwithin a few months, but the paraesthesiae, although lessintense, persisted till the time of admission. Six monthsbefore admission she found that her right leg and footwere becoming clumsy.When she arrived in hospital, she described these

paraesthesiae in the right upper limb as "irritating and

*Markle Scholar from the University of Pittsburgh.

bothersome" but not as a true pain; she said that theskin in the affected region was unduly sensitive, anythingrubbing it causing an increase in the paraesthesiae andmaking the sensation very unpleasant. She stated thathot and cold felt more intense in this area of skin,although she had burned the little finger without noticingany pain. The appreciation of light touch and two-pointdiscrimination was diminished over all the fingers ofthe right hand and on the thumb; these changes weremost marked in the thumb and index finger. Theparaesthesiae of which she was complaining wereaggravated by stroking or scratching the thumb, theindex, the radial side of the forearm, the outer surfaceof the upper arm, and also a small area on the anteriorchest well just below the clavicle. The right biceps jerkwas diminished. All rapid movements of the right footwere impaired; and the plantar response on the rightwas the Babinski type.The cerebrospinal fluid contained 6 lymphocytes and

0 8 mg. of protein per ml. Radiographs of the cervicalspine, a myelogram, and an air encephalogram werenormal.

This patient's main symptoms and signs indicatedinvolvement of several cervical roots or spinal segmentsof the cord on the right, and, in particular, the sixthcervical. The damage to the long tracts affecting themovements of the right lower limb had occurred morerecently. It was thought most likely that the patienthad disseminated sclerosis; damage to the nerve rootsand spinal cord on the right side by prolapsed discs wasconsidered as an alternative diagnosis.

Protocol of Experiment.-Before the injection of theright median nerve, the pins and needles sensation wasconfirmed to be present mainly in the palmar surface ofthe right thumb; the cramping sensation was presentin the entire right hand. The sensations were describedas unpleasant; they were aggravated by stroking.The first attempt at injecting the median nerve above

the elbow failed, the medial cutaneous of the forearmbeing injected in error. In one sense, this injection thusacted as a control. The patient knew she had had aninjection, and she experienced some numbness in thelimb but this injection had no effect on the paraesthesiae.The median nerve was then injected with 1% ligno-

caine successfully just distal to the elbow. There ensueda rise in temperature and much diminution in sensibility:

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R. F. KIBLER AND P. W. NATHAN

TABLE IPATIENTS INVESTIGATED

Main Segments Kind of StructurePtIenitis Diagnosis Site of Lesion where Pain or Pain or Blocked ResultsInitialsy(presumed) ParaesthesiaePainestm by Local

are Felt Paaetesa Anaesthetic

Probably disseminatedsclerosis, possiblyprolapsed cervicaldiscs

Carcinoma ofbronchus spreadingintc spinal canal

Disseminated sclerosis

Disseminated sclerosis

Syringomyelia

Intramedullary spinalcord lesion

Carcinoma of cervixuteri

Prolapsed lumbardiscs

Spinal roots

Spinal roots

Posterior rootentry zone

Fasciculuscuneatus

Posterior horn

Spinothalamidctract

Sacral roots

Spinal roots

6th cervical

7th and 8thcervical

8th cervical

7th and 8thcervical

6th, 7th, and8th cervical

5th lumbar to5th sacralinclusive

5th lumbar to5th sacralinclusive

3rd lumbar

the sharp and painful element of pin prick throughoutthe median distribution had gone, but touch and pressurewere still felt. Both pins and needles and the crampingsensation disappeared completely. When the skin on

the outer side of the right arm and on the anterior aspectof the chest was rubbed with the examiner's finger, theregion which had previously given rise to the unpleasantdysaesthesiae, now felt "smooth and velvety"; it hadno unpleasant components and no longer had thesensation of pins and needles.

Fifteen hours later the patient still had no return ofthe pins and needles and no cramping feeling; thus thisrelief outlasted any objective effects of the local anaes-

thetic. Scraping a pin across the skin supplied by themedian nerve no longer caused the unpleasant dysaesthe-siae, but scraping it across the skin below the claviclecaused them.An incomplete block of the median nerve stopped

spontaneous paraesthesiae and the unpleasantdysaesthesiae produced by firm stroking of the skin;the block was differential, in that it affected mainlythe sympathetic fibres and those subserving pain.The relief was not restricted to the median territorybut extended from the fourth to the seventh cervicaldermatomes. The effect outlasted the analgesiainduced by the local anaesthetic solution.

J.N. (National Hospital No. 81349).-This 36-year-oldman was admitted to the National Hospital in November,1958. Six months before admission a lobe of the leftlung had been removed for carcinoma of the bronchus.A few weeks after the operation, the patient began tohave pain down the inner side of the left forearm,extending into the fourth and fifth digits, where he also

Unpleasantpins andneedles andsensation ofcramp

Pain

Burning pain

Pins andneedles

Aching pain

Burning pain

Pain

Burning pain

Median nerve

Ulnar nerve

Ulnar nerve

Ulnar nerve

Ulnar nerve

Sacral roots

Sciatic nerve

(a) Skin(b) Femoral

nerve

Removal of pins andneedles and sensation ofcramp. They remainedabsent several hoursafter anaesthesia hadworn off.Removal of pain. It re-mained absent severalhours after anaesthesiahad worn off.

Permanent relief of painafter second injectionRemoval of pins andneedlesRemoval of pain

Removal of pain

Removal of pain

Removal of painRemoval of pain; it re-mained absent 46 hoursafter anaesthesia hadworn off

developed tingling and numbness. Two months beforeadmission a pain of similar quality and distribution hadappeared in the right upper limb. Weakness developedrapidly in the left and then in the right hand. Two weeksbefore admission the patient had developed severe painbetween the scapulae and weakness of both lower limbs.On examination, he had much weakness of both upper

limbs, more of the left than the right, and wasting of themuscles of both hands and of the left forearm. Thebiceps and triceps jerks on the left were absent. Therewas weakness of both lower limbs, both plantar responseswere of the Babinski type, and there was bilateral ankleclonus. All forms of sensibility were diminished over

the last three fingers and on the distal part of the ulnaraspect of both forearms. There was some loss of painand touch sensibility over the trunk and lower limbsbelow the level of the fourth thoracic segment.Lumbar puncture revealed a partial block; the

cerebrospinal fluid contained 4 cells and 0-6 mg. ofprotein per ml.

In this patient the carcinoma had spread into thespinal canal, compressing the cord. Most of the painwas in the left upper limb distal to the elbow; it was

associated with diminution of sensibility in the seventhand eighth cervical dermatomes.

Protocol of Experiment.-Before the injection to blockthe ulnar nerve, the patient was in obvious distress andhis face was pouring with sweat. The pain was distal tothe elbow, and was maximal in the ulnar territory of thehand and along the ulnar border of the forearm. Helocated it as deep, "right through the fingers", but notin the thumb or index finger. The ulnar nerve wasinjected in its groove with 2% lignocaine. Even beforethe patient told us that his pain had been relieved, it wasobvious, from the ceasing of the sweating on the face and

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RELIEF OF PAIN BY NERVE BLOCK DISTAL TO A LESION

the other signs of distress. Within five minutes of theinjection, there was complete loss of sensibilitythroughout the ulnar distribution. The pain disappearedcompletely from this limb and the forearm and handfelt "comfortably warm"; in contrast, the right upperlimb felt cold and he became more aware of pain in theright upper limb, which before the injection had beenminimal. The pain remained absent from the left upper

limb for about two hours.

Blocking the ulnar nerve stopped the pain in theleft forearm; this pain had been present in a more

extensive area than the cutenous distribution of theulnar nerve. The pain-relieving effect outlasted theduration of the local anaesthetic for about 30minutes.

G.N. (National Hospital No. 52599).-This 37-year-oldman was in the National Hospital in 1954. He hadcomplained of a varying state of clumsiness of the rightlimbs, attacks of unsteadiness, and of slurring of hisspeech. The course of the disorder had been charac-terized by remissions and exacerbations. He was foundto have, besides the obvious slurring of speech, a mildright hemiparesis. The cerebrospinal fluid contained15 cells and 0 55 mg. of protein per ml. and the Langecurve was 122211000; the Wassermann reaction inblood and cerebrospinal fluid was negative.

His unsteadiness and dysarthria gradually improved;but in September, 1957, he developed an intense burningpain in the fourth and fifth digits and along the medialborder of the left hand. During the first few months of1959 his gait became unsteady and he developed blurringof vision. It was then found that visual acuity wasreduced and that the right optic disc was swollen; therewas nystagmus, an intention tremor in the upper limbs,and both plantar responses were of the Babinski type;Lhermitte's sign was also present. Appreciation of twopoints, passive movements, and vibration was diminishedon the fourth and fifth digits of the left hand; two-pointdiscrimination was equally affected on the median andulnar cutaneous distribution of the fourth digit. Whenthe fifth, fourth, and medial side of the third left digitswere slightly scratched with a pin, the patient experiencedan unpleasant spreading sensation like an electric shock;this was not an exaggeration of his constant burningpain.The diagnosis was considered to be disseminated

sclerosis, and the pain was thought to be due to a plaquein the eighth cervical posterior root entry zone.

Protocol of Experiment.-The left ulnar nerve was

injected with 2% lignocaine in the ulnar groove. Withinthree minutes, all the burning pain left the fifth digit,and within five minutes it had all gone from both digits.At this time there was complete loss of sensibility withinthe ulnar distribution. As sensibility returned to theulnar area, the pain returned. By the time sensibilitywas fully normal, the pain was at its full intensity, andscratching with a pin caused the usual dysaesthesiae.Twelve days later, the patient returned to say that

since this injection the base of the little finger had been

free from pain and that there was also less pain in thefourth finger than before the injection.The ulnar nerve was again injected in the ulnar groove

with 2% lignocaine. As the total anaesthesia and motorparalysis came on, so the pain went away. One hourlater sensibility returned except for slight diminution inthe appreciation of touch and pin prick; pricking nolonger gave the usual dysaesthesiae. The burning painremained absent.Two weeks later the patient returned to say that since

the previous injection of the ulnar nerve none of theburning pain had returned. He had, however, a deepache in the fourth and fifth digits and he wondered if thishad been present before and that he simply had notnoticed it on account of the burning pain. On examina-tion of the digits it was found that scratching with thepin no longer caused the dysaesthesiae, but gave a normalsensation of being scratched, though to a slightly lessthan normal degree.Two months later the patient was still free from the

burning pain. When the skin of the fourth and fifthdigits was stroked with a pin there were no dysaesthesiae:"it just feels rough". The deep pain was present, butthe patient said he might go four or five days withouthaving it.

It was considered that the pain and dysaesthesiaein this case were due to a plaque in the root entryzone of the eighth cervical posterior root. Thesituation of dysaesthesiae and of the pain wastypical of a lesion affecting the eighth root and notof the ulnar nerve; yet blocking the ulnar nervecompletely stopped the pain throughout the wholearea. A second blocking of the nerve gave lastingrelief of the burning pain, but apparently unmaskeda deep pain. After these injections the sensibilityof the affected digits became much more normal;although the appreciation of sensory stimuli re-mained slightly diminished, the painful dysaesthesiaewere no longer present.

A.R. (National Hospital No. 83923).-This 56-year-oldwoman was admitted to the National Hospital in March,1958. Eighteen months before admission she had be-come aware of a sensation of pins and needles in thethird, fourth, and fifth digits of the right hand; it hadcome on insidiously and was present constantly. Oneyear before admission she had had an episode of vertigo,and after this, walking had become unsteady. Sevenmonths before admission the right lower limb hadsuddenly become weak, and since that time the weaknesshad gradually become more severe.When examined in the hospital there was nystagmus

of rotatory type on looking to both sides, the tendonreflexes were more active in the right limbs than in theleft, and there was a spastic paresis of the right lowerlimb. In the right upper limb vibration was felt to adiminished degree on the ulnar border of the hand andwrist, and two points were appreciated at a distance of8 mm. on the right fourth and fifth digits comparedwith 5 mm. on the left. No form of stimulation of the

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fingers had any effect in intensifying or altering the pinsand needles sensation. The cerebrospinal fluid contained2 cells and 0-45 mg. of protein per ml.; the Lange curvewas normal and the Wassermann reaction negative.A myelogram was normal.The diagnosis was considered to be disseminated

sclerosis, and the painless pins and needles sensation werethought to be due to a plaque affecting the fibres of thefuniculus cuneatus derived from the seventh and eighthcervical dermatomes.

Protocol ofExperiment.-The patient was experiencingthe usual constant pins and needles in the right third,fourth, and fifth digits before the experiment. The rightulnar nerve was injected in the ulnar groove with 1%procaine. Within 10 minutes the pins and needlessensation had completely gone. The ulnar nerve blockwas incomplete. The patient had a mild feeling oftightness in the ulnar distribution. This side of the handwas warm and fully vasodilated; there was a diminutionin the sensation of pain on pricking and only very slight,if any, diminution in touch sensibility. One hour laterthe feeling of tightness was diminishing and the pins andneedles sensation was returning, and one and a half hoursafter the injection the feeling of tightness had gone andthe pins and needles sensation had returned to its originalintensity.The paraesthesiae and the type of loss of sensi-

bility were thought to indicate a lesion of thefasciculous cuneatus, involving particularly thefibres from the seventh and eighth cervical segments.Blocking the ulnar nerve stopped the paraesthesiaecompletely. This effect persisted as long as the localanaesthesia lasted.

H.G.-This 29-year-old man was admitted to theVeterans Administration Hospital, Pittsburgh, inSeptember, 1959. He was complaining of weakness inthe right upper and lower limbs and pain in the righthand. He had had pain in the right hand and forearmfor 10 years, and over the same period the right upperlimb had become progressively weaker and the rightlower limb had become clumsy. He had occasionallyburned his right hand or fingers while smoking and yethad felt no pain. One year before admission to theVeterans Administration Hospital, a laminectomy hadbeen carried out to lay bare the spinal cord from itsfirst to its fourth cervical segments; no lesion had beenfound and the cord had appeared quite normal.

In September, 1959, he complained of pain of a boring,aching kind, situated deep inside the palmar and dorsalaspects of the hands; the previous pain in the forearmhad gone. This pain was unaffected by movements ofthe hand, shoulder or neck, by stroking or scratching thehand, or by any manoeuvre designed to increase it.Examination showed that there was almost completeloss of sensibility of pain and temperature on the right,from the second cervical to the sixth thoracic segmentsinclusive; in this region touch and vibration were nor-mally felt and the sense of position and movement wasunimpaired; but two-point discrimination was slightlyimpaired on the right hand and digits. In the right upper

and right lower limbs there was weakness and increasedtone. The deep reflexes were absent in the right upperlimb; in the right lower limb they were pathologicallyincreased, there was ankle clonus, and the plantarresponse was of the Babinski type. There were scarsdue to previous burns on the right hand and fingers.Lumbar puncture revealed no block; there were

3 lymphocytes and 0-3 mg. of protein per ml.; theWassermann reaction was negative.The diagnosis was considered to be syringomyelia;

the deep type of pain was thought to be due to involve-ment of fibres in the posterior horn of the sixth, seventh,and eighth cervical segments.

Protocol of Experiment.-The right ulnar nerve wasinjected in the ulnar groove with 2% lignocaine on threedifferent occasions. The results on each occasion werethe same. Within five minutes of the injection, all painleft the entire hand. The pain returned about an hourafter the injection, coming back as the motor paralysiswent off. The relief of pain never outlasted the durationof the anaesthesia. On each occasion the removal of thepain followed the same course: it first went from theregion of the ulnar distribution, and last went fromthe dorsal part of the lateral half of the hand.The pain of a deep kind, typical of syringomyelia,

located deep to the sixth, seventh, and eighthdermatomes was completely relieved by blockingthe ulnar nerve. This effect persisted as long as thelocal anaesthesia lasted.

G.B. (National Hospital No. 86061).-This 62-year-oldwoman was admitted to the National Hospital in May,1959. Her main complaint was of a "scalding pain" inboth buttocks and down the right lower limb, which hadbeen present for two years. In January, 1957, the leftlower limb had "suddenly given out" and she hadfallen; over the next four days she had continuous painin the back, the abdomen, and down both lower limbs.She was admitted to a local hospital where severe weak-ness and loss of sense of position in the left lower limbwas found, with analgesia over the right side of the bodybelow the fourth thoracic dermatome. Lumbar puncturerevealed no block; there were 3 lymphocytes and 0-8 mg.of protein per ml.; the Wassermann reaction wasnegative. When she left her local hospital five weekslater the movements of the left lower limb were im-proving, much sense of position and movement had beenregained, and all pain had gone. In June, 1957, she firstdeveloped the scalding pain in both buttocks and downthe right lower limb into the heel, which had persisted tothe time of admission. She found also that from thewaist down, particularly on the right side, any touchcaused an unpleasant "queer" feeling; this was not thesame as the spontaneous burning pain. On examination,she was found to have a spastic paresis of the left lowerlimb, associated with diminution in the sense of positionand movement, and inability to feel vibration. Belowthe fourth thoracic dermatome all forms of cutaneoussensibility were abnormal. On the right, pain sensibilitywas almost absent below the third lumbar dermatome;between the third lumbar dermatome and the fourth

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thoracic dermatomes, pinprick caused a most unpleasantkind of pain-"it seems to go in further and be morepointed"; here the sensibility of warmth and cold weresimilar, being absent below the third lumbar dermatome,and abnormal below the fourth thoracic derma-tome. On the right below the twelfth thoracic dermatometactile stimuli gave a tingling sensation; this was mostmarked where the loss of pain sensibility was greatest,and there such stimuli also gave an unpleasant rawsensation. On the left side of the body between the sixthand the twelfth thoracic dermatomes the sensation oftouch was reduced and distal to these segments it wasvery much reduced; in the left buttock, touch produceda sensation of tingling.

It was considered that the lesion giving rise to thisclinical picture was an intramedullary lesion of the leftside of the cord, extending from the sixth to the twelfththoracic segments; this was thought to be some sort ofvascular accident. As the patient had recovered fromthe immediate acute effects, the scalding pain had comeon gradually. The region in which she had this painmost severely was below the third lumbar segment, inthe area where pain and thermal sensibility were mostdiminished and where tactile stimulation gave the un-pleasant raw sensation. It was observed that she had thesame pain in the left buttock, where, although tactilestimulation gave a similar raw sensation, there was nochange in normal appreciation of painful or thermalstimuli. This finding was difficult to explain satisfactorily.

Protocol of Experiment.-A spinal anaesthetic wasgiven in the form of I n ml. of heavy "nupercaine" whichwas injected between the fifth lumbar and first sacralspines, the patient lying on her right side, with the caudalparts of her body lower than the cranial. It achievedtotal analgesia bilaterally over the sacral third, fourth,and fifth dermatomes. Tactile sensibility was difficultto judge on the left as it was always so diminished; on theright it was severely diminished, but not absent, over thebuttock only. This injection removed all the pain inboth buttocks and the right thigh; it had no effect onthe pain in the right leg or right heel. The patient hadno subjective sensation of numbness and she thereforehad no idea of the presence, extent, or of any change insensibility due to the spinal anaesthetic.

Although the pain was clearly of central origin,anaesthetizing the nerve roots of an area in whichthe pain was felt removed the pain. In this case theremoval of pain did not outlast the duration ofanaesthesia. Also blocking some of the nerves ofthe region in which pain was felt did not remove thepain from the whole region. Indeed, the fact thatthe patient did not know which regions had beenrendered analgesic and anaesthetic, and that herpain went only from the area supplied by the blockednerves and not from the area supplied by unaffectednerves, shows that the relief of pain was not due tosuggestion or to similar mechanisms.

L.R. (National Hospital No. 74975).-This 37-year-oldwoman was in the National Hospital in 1958. One year2

previously, a panhysterectomy had been performed fora squamous-cell carcinoma of the cervix uteri. Twomonths after this operation she had developed a constantpain in the right hip, which extended down the back ofthe entire lower limb into the dorsum of the foot. Thishad become so severe that she was taking pethidinethree-hourly. She described the pain as "dreadful" andin character "like red hot needles". More recently shehad developed foot drop on the right and the right lowerlimb had become oedematous. There was a large massfilling the retrovesical space, and in both inguinal regionsthere were large, very hard glands. There was diminutionof sensibility in the fifth lumbar and all the sacraldermatomes on the right. A pinprick of 60 g. weightwas felt as a blunt touch, but one of 140 g. was felt aspainful; it did not feel like a pin, but like a scratch.Cottonwool was felt everywhere except along the backof the leg below the popliteal space. Temperatures of12°C. and 50°C. were not felt in the fifth lumbar orsacral dermatomes, but radiant heat and ice and ethylchloride spray were felt as such, except in a smaller areaon the back of the leg. All muscles on the right suppliedby the sciatic nerve and the pudendal plexus wereparalysed; the right ankle jerk and plantar responsewere absent. The flare of the triple response was absentin the fifth lumbar and all sacral dermatomes on theright.The carcinomatous tissue was considered to be lining

the right wall of the pelvis, involving the lumbo-sacraltrunk and all the nerves on the right forming the sacraland pudendal plexi; this involvement was at or peripheralto their ganglia.

Protocol ofExperiment.-Pain of the usual severity waspresent throughout the right lower limb, maximal in thebuttock and in the sole of the foot. The sciatic nervewas injected with 1% lignocaine just below the natalcleft. Within five minutes all the pain went, except thatin the buttock. It remained absent for one and a halfhours.

Blocking the sciatic nerve removed the severepain from the territory of this nerve; it had noeffect on pain felt in regions supplied by other nervesof the sacral and pudendal plexi.

J.H.P. (National Hospital No. 81235).-This 67-year-old man was in the National Hospital in 1958. Eighteenmonths before he had developed a painful prickingsensation over the anterior surface of the right thigh,and the leg had become weak. In November, 1957, oneyear before admission, the pain had become worse and itconsisted then of knife-like jabs of pain in the anteriorthigh. He was admitted to the Atkinson MorleyHospital. There Mr. L. S. Walsh made a diagnosis ofprolapsed intervertebral disc at the second and thirdlumbar level, and decided to operate. At the operationhe found that the dura mater was compressed up againstthe lamina of the third lumbar vertebra, and the discbetween the second and third lumbar vertebrae wasabnormally soft and was causing a marked bulge intothe spinal canal. A number of fragments of this discwere removed; after their removal there seemed to be a

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satisfactory decompression of the spinal roots. Thisoperation was followed by an uneventful convalescence;the strength of the leg improved and the loss of sensi-bility regressed, there remaining a very slight loss in thethird and fourth lumbar dermatomes. The pain at firstwas relieved but it began to return about six weeks afterthis operation.When the patient came into the National Hospital in

September, 1958, the pain was located in the distributionof the cutaneous branches of the femoral nerve. It wasworse than it had been before removal of the prolapseddisc and more extensive. There was a continuoustingling in the skin and a deep, burning pain beneath theskin; in addition, whenever this area of skin was touched,the stimulation gave rise to little electric-shock-likesensations.There was slight wasting and weakness of the right

quadriceps and weakness of the flexors of the thigh;raising the fully extended right lower limb caused painin the lower spine. The right knee and ankle jerks werediminished, the plantar responses were normal. Therewas loss of sensibility in the distribution of the anteriorfemoral cutaneous nerve, and slight loss in that ofthe lateral femoral cutaneous and saphenous nerves.In the former territory pinprick was felt only as blunttouch, in the latter territory, it was slightly diminished;on the dorsum of the foot a very slight loss to pinprickwas detected. On the front of the thigh sometimesa very heavy pinprick gave a sensation like a localelectric shock. Cottonwool touches were felt to adiminished degree in the fourth and fifth dermatomes.The cerebrospinal fluid contained 4 cells and 1 mg. ofprotein per ml. On myelography changes suggestingarachnoiditis were seen in the region of the formeroperation.A sphygmomanometer cuff was placed on the left

upper limb in order to render this limb ischaemic for30 minutes, to induce the various sensations occurringduring and after circulatory block; this was done so thatthe patient could compare these induced sensations withhis spontaneous ones, and to enable him to give us abetter concept of his pain and paraesthesiae. He reportedthat the pain in the fingers induced at the end of theperiod of ischaemia when only C fibres are conductingwas identical with his constant pain in the thigh. Healso stated that he sometimes got the sensation ofpseudo-cramp in the thigh and the pricking part of thepost-ischaemic paraesthesiae.The diagnosis of prolapsed intervertebral disc had

been confirmed at operation. Although much disc tissuehad been removed, both the symptoms and signs returnedin at least as severe a form as they had been beforeoperation.

Protocol of Experiment.-An injection of 1% ligno-caine with hyaluronidase was given subcutaneously intothe region supplied by the medial femoral cutaneousnerve. By the time this area was completely insensitiveto tactile and painful stimuli, all the pain had gone fromthe right lower limb; the only pain remaining was inthe back. Thus the pain had gone from the entire limb,not only from the distribution of the cutaneous branches

of the femoral nerve; furthermore he found he couldflex the knee without getting the unpleasant tight feelingthat this movement usually produced. The pain re-mained absent for three hours, which was longer than theduration of the local anaesthesia.On another occasion, an attempt was made to inject

the right femoral nerve in the femoral triangle with1% lignocaine. This injection, however, blocked themuscular branches to the quadriceps and the saphenousnerve; the anterior femoral cutaneous nerve escaped,Nevertheless as soon as the territory of the saphenousnerve was insensitive to touch and pinprick, the pain inthe lower limb went. It is to be noted that the area ofmaximal pain and abnormality of sensibility, that of theanterior femoral cutaneous nerve, was unaffected by theinjection, except for slight loss of sensibility in its mostdistal distribution; and the skin of this region retainedits abnormal characteristics with regard to sensibility.And yet this injection removed all the pain in the lowerlimb. Further, the effects of this injection in relievingpain lasted 48 to 60 hours. Sixteen hours after theinjection the following change in sensibility was noted.The injection had been carried out by one of us unknownto the other. The latter, visiting the patient 16 hoursafter blocking of the saphenous nerve, found an im-provement in the sensibility of the skin in the distributionof the anterior femoral cutaneous nerve; althoughobjectively there was no change, the patient when he didfeel a hard pinprick here no longer felt it like a littleelectric shock but felt it like a normal painful andpointed pin.

In this patient a lesion, proved at operation,was affecting the second, third, fourth, and to someextent the fifth lumbar roots. Blocking of impulseseither from the cutaneous distribution of the secondand third posterior root or from that of the fourthroot removed the pain throughout the distributionof all the roots; further, after one of these injectionsthe pain remained absent for 48 hours; andanaesthetizing the territory of the fourth lumbardermatome improved the sensibility of the secondand third lumbar dermatomes.

DiscussionBlocking an afferent pathway at a point distal to

the site of a lesion stops the spontaneous sensationswhich result from the lesion. It is reasonable toassume that a lesion situated on an afferent pathwayis the originator of the discharge of impulses in thecontiguous nerve fibres and that this is the cause ofthe "spontaneous" sensations experienced; henceit is somewhat surprising to discover that theapparently less probable alternative theory iscorrect: that the pain and paraesthesiae are due toimpulses arriving from the periphery, which aresomehow altered by the lesion. Since we have nofurther evidence to present on the mechanism of thepain in these cases, there seems little point in

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suggesting various conjectures to account for it.It is necessary, however, to discuss whether thephenomena reported here can be accounted forentirely by events at the site of the lesion on thenerves or whether they can be accounted for byinvoking factors in the central nervous system.

It is possible that the pathological lesion of thenerves gives rise to an artificial synapse, similar tothat produced experimentally by Granit, Leksell,and Skoglund (1944). They showed that in cats,if a nerve is cut and the motor root is stimulated,action currents can be picked up from the sensory

root; and also they can be picked up from the motorroot when the sensory root is stimulated, thoughin this case the stimulus needs to be much stronger.The place where the transmission from one lot ofnerve fibres to the other takes place, seems to be atthe cut end of the nerve. In order to obtain such an

artificial synapse they then found that it was un-

necessary to cut the nerve across; a ligature roundthe nerve, tight enough not to damage normal distalconduction, suffices to make such a synapse. Itmay be suggested that with naturally occurringlesions impulses from the periphery arriving at thesite of the lesion become switched into fibres whosecentral terminations end in parts of the brain wherepain and paraesthesiae are experienced; whenimpulses are blocked from reaching the site of thelesion, impulses cannot be switched to these fibresand so there is silence. A similar mechanism toaccount for causalgia has previously been suggestedby Doupe, Cullen, and Chance (1944) and byNathan (1947).But such a mechanism cannot account for all the

phenomena reported here. For the followingobservations cannot be explained without con-

sidering that blocking impulses from the peripherycause some changes in the central nervous system.The first of these observations is that blocking thenervous conduction from a part of a territory inwhich the pain or paraesthesiae are arising issufficient to stop the pain and paraesthesiae through-out the entire territory; for this to occur, theregion from which the nervous pathway is blockedneed not be that in which the pain or paraesthesiaeare maximal. An instance of this was J.P., in whomblocking the saphenous nerve removed all the painin the lower limb, although the pain felt in thesaphenous territory was minimal in comparison withthat felt in the thigh. In many cases the period ofrelief of pain or paraesthesiae outlasted the durationof the block of the peripheral pathway; in one case

the relief was permanent. And there is also the factthat in the cases where the pain or paraesthesiaehave been relieved, the actual sensibility of the skinof the part has been rendered more normal. This

applies also to regions of skin within the area of painbut outside the territory of the nerve that wasblocked. This improvement in sensibility will notbe discussed further here, as it will be treatedseparately in a later paper.One might suggest that an explanation of the facts

described is that the local anaesthetic solutiontracked up the peripheral nerves to the site of thelesion in the nerve root or in the spinal cord. Thissuggestion seems to us unlikely but not one that canbe dismissed out of hand. It would entail thesupposition that the anaesthetic solution in adequateconcentration reaches the spinal roots, root entryzone, or the spinal cord from a nerve injected at thelevel of the elbow within a few minutes. Yet ithas been shown by Merrington and Nathan (1949)that 2 ml. of 200 procaine solution with adrenalinewhen injected into the ulnar nerve at the wristspreads within a few minutes for a proximal dis-tance ofat least 8cm. More careful work on the spreadof substances when injected intraneurally has beenreported in an important paper by Brierley andField (1949); they studied the spread of radioactivephosphorus from the sciatic nerves of the rabbit.In one rabbit in which the injection into the sciaticnerve was at the level of the great trochanter of thefemur (incidentally at the same level as our injectionin L.R.) the tracer substance was found nineminutes after injection in the segments of the spinalcord from which the sciatic nerve takes origin. Thuswe suggest that the spread of the local anaesthetic upto the roots or spinal cord is not an impossibleexplanation of our findings, but it is improbable.

If all the facts reported here cannot be explainedby events taking place at the site of the lesion in thenerves, if they cannot be explained by spread of thelocal anaesthetic to the site of the lesion or intothe affected spinal segments of the cord, then we haveto conclude that blocking impulses at a peripherallevel has definite effects on events in the centralnervous system, presumably at a spinal level.

If this suggestion is correct, it is concluded that astate of excessive excitability has been engenderedin the central nervous system; and that this stateis in a region of the central nervous system to whichthe nerve fibres from the lesion are running. Ifthere is such a state, it is surprising to find howeasily it can be made to subside: half an hour'sanaesthesia may suffice to do so for periods of atleast two months.The next question that comes to mind is whether

blocking of impulses from the periphery will relievethe pain in all cases where there is a lesion on anerve, posterior nerve root, or afferent path in thecord. Obviously such a question cannot beanswered. The cases reported here are an un-

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selected sequence of cases in which a lesion on anafferent pathway was associated with pain andparaesthesiae. In no cases have we blocked theperiphery without obtaining this result. The factthat we have not found any counter-examples doesnot mean that we believe that they do not occur.Our purpose was to investigate the cases we foundwhere it was evident that the pain or paraesthesiaewere arising central to the incoming peripheralnerves; in these few cases the pain or paraesthesiaewere stopped by blocking the peripheral pathway.Over the past 10 years one of us (P.W.N.) has

anaesthetized the affected area of skin in many casesof post-herpetic neuralgia; this may be consideredto be a similar situation. But here the results areless definite. Usually some of the pain is relieved bysubcutaneous injection of local anaesthetic. Cer-tainly if the skin is rendered anaesthetic and anal-gesic, any pain usually felt in the skin ceases;typically the patient states that the burning hot partof his pain has gone, but the gripping aching anddeeper part of his pain remains. This part of thepain is not usually relieved by anaesthetizing themuscles. It is also relevant that in such casesthe operation of posterior rhizotomy is notoriouslyunsuccessful; and this cutting of the roots might be

thought of as being comparable to anaesthetizingthe peripheral pathway, as was done in theseexperiments.

SummaryThe pain and paraesthesiae associated with lesions

in peripheral nerves, nerve roots, root entry zone,posterior columns, and spino-thalamic tract can beprevented by blocking the nerves distal to the lesion.The relief of pain and paraesthesiae may outlast theduration of the anaesthesiae. Blocking of impulsesfrom a large part of the region supplied by theaffected nerves may remove the spontaneous painand paraesthesiae from the whole of the region.

We wish to thank the physicians and surgeons of theNational Hospital, Queen Square, who were kind enoughto put their patients at our disposal for this investigationand Dr. E. Arnold Carmichael for his encouragementand facilities to do this work.

REFERENCESBrierley, J. B. and Field, E. J. (1949). J. Neurol. Neurosurg. Psychiat.,

12, 86.Doupe, J., Cullen, C. H., and Chance, G. Q. (1944). Ibid., 7, 33.Granit, R., Leksell L., and Skoglund, C. R. (1944). Brain, 67, 125.Merrington, W. R.: and Nathan, P. W. (1949). J. Neurol. Neurosurg.

Psychiat., 12, 1.Nathan, P. W. (1947). Brain, 70 145.

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Documents

OFPAIN AND PARAESTHESIAE BY NERVE BLOCK LESION · those of pain and painful pins and needles; when it affects the posterior columns of the cord, the sensation is one of painless pins