Investigation of disorders of the anorectum and colon

Annals of the Royal College of Surgeons of England (1985) vol. 67

Investigation of disorders anorectum and colon

of

the

MICHAEL M HENRY FRCS* Honorary Consultant Surgeon

STEPHEN

J

SNOOKS FRCS

Research Fellow

PHILLIP R H BARNES MRACP Research Fellow

MICHAEL SWASH MD FRCP MRCPatht Director Sir Alan Parks Physiology Unit, St. Mark's Hospital, London Key words: PHYSIOLOGY; CONSTIPATION; ANUS; RECTUM; ENCOPRESIS

Sunmary Previously, investigation of disorders of the anorectum and colon have been limited to manometric, external anal sphincter muscle electromyographic and contrast radiological techniques. In this paper we describe other investigative techniques recently developed at St. Mark's Hospital, London and their application in the investigation of certain disorders of the anorectum and colon. Introduction Certain physiological techniques have been developed to investigate disorders of function of the anal sphincters, rectum and pelvic floor in our laboratory. The range of disorders for which we have found these tests helpful is listed in Table I. Although a detailed clinical examination may be sufficient to establish a diagnosis in many of these conditions, the methods we describe here may contribute substantially to management by providing an objective assessment of function as well as, in some cases, identifying the anatomical site of the lesion. The majority of techniques described here require little technical expertise and employ apparatus which is standard and readily available in most centres. TABLE I Range of disorders for which physiological investigation is employed at St Mark's Hospital Congenital Acquired

Hirschsprung's disease Rectal atresia Anorectal incontinence Rectal prolapse Solitary rectal ulcer Constipation Descending perineum syndrome Neurological diseases

PHYSICAL EXAMINATION

Simple inspection of the perineum may provide considerable information. The following features should be looked for: Correspondence to: M M Henry, St. Mark's Hospital, City Road, London ECIV2PS. * Consultant Surgeon, Central Middlesex Hospital. t Consultant Neurologist, The London Hospital.

(a) soiling of the perianal skin, (b) the cutaneous anal reflex, (c) a patulous or closed anus, (d) prolapse complete or partial at rest and during defaecation straining, (e) perineal descent, defined as descent of the plane of the perineum below that of the bony outlet of the pelvis during a straining effort and (f) local scarring or fistula. From digital examination of the anal canal an approximate estimate of anal sphincter function can be made. Resting tone is an index of internal anal sphincter function (1). The somatic musculature can be assessed by determining the amplitude and maximum duration for which voluntary contraction can be sustained. The amplitude generated by reflex contraction instituted by a maximum cough effort can also be palpated. Finally the puborectalis shelf, palpable posteriorly in the upper anal canal, should be assessed. Proctoscopy is indicated in the patient with possible mucosal prolapse. Sigmoidoscopy is performed to exclude a neoplasm and to identify mucosal changes consistent with traumatic proctitis in those patients with prolapse or a solitary rectal ulcer. Wherever the true diagnosis of these changes is in doubt biopsy should be performed. The techniques ANAL MANOMETRY

Manometry is a crude means of quantifying external and internal anal sphincter function and may also provide a noninvasive means of establishing a diagnosis of Hirschsprung's disease. In our laboratory, pressures are measured using a closed water-filled system consisting of a polythene tube of 2 mm external diameter to one end of which is attached a 4 mm diameter microballoon. The balloon probe is connected to a transducer, the signal from which is amplified and displayed on a suitable recording device. After calibration, anal pressures are measured at one centimetre intervals firstly in the resting state and secondly during periods of voluntary contraction of the external anal sphincter. Using this technique the range for resting pressure is 60- 100 cm. water. The intra-anal pressure is doubled during voluntary contraction in the normal control. Internal anal sphincter contraction can be inhibited by rectal distension (2). This reflex is mediated by means of local visceral nerve plexuses situated in the submucosal and

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myenteric planes. The integrity of the reflex is tested by recording the resting anal pressure while 50 ml. of air is rapidly introduced into a second balloon which has previously been introduced into the rectum via a proctoscope. BALLOON PROCTOGRAPHY

Balloon proctograms provide a visual assessment of the pelvic floor in the resting state and during defaecation straining (3). A soft rubber balloon with a 3 cm teat is attached to a plastic catheter of 3 mm external diameter which is fitted at its proximal end with a 3-way tap. With the patient placed in the left lateral position, the balloon is inserted into the rectum and positioned so that the teat lies within the anal canal. The balloon is filled with 100 ml of dilute barium sulphate via the plastic catheter. A metal marker is attached with tape to overlie the pubic symphysis. The patient is placed on a perspex commode seat and lateral radiographs taken at rest and during a maximum straining effort. With this technique the distal rectum and anal canal are clearly outlined. The anorectal angle (normal = 90-100°) can be measured employing the axes of the anal canal and the floor of the rectum posteriorly. The pubococcygeal line is drawn from the tip of the coccyx to the postero-inferior margin of the pubic ramus. The relationship between the bony outlet of the pelvis and the anorectal angle, the plane of the pelvic floor, can thus be investigated objectively. Normally the pelvic floor lies at a plane approximately 1 cm below that of the pubococcygeal line. BALLOON EXPULSION TEST

A rubber party balloon is attached to a 10cm length of plastic tubing of 3 mm external diameter to which a 3-way tap is fitted at its distal end. On bench testing the balloon assumes a spherical shape of 3.5 cm diameter when filled with 50 ml of water. With the patient in the left lateral position and knees flexed, the empty balloon is inserted into the rectum and slowly inflated with 50 ml of warm tap water. The patient is instructed to expel the balloon from the rectum with a straining effort. If unsuccessful, weights may be added to the balloon by means of a system of pulleys and the amount required before the balloon can be expelled by the patient is then recorded.

Using this technique Preston and Lennard Jones (4) found that all their controls could readily expel the balloon without the addition of extra weights. In contrast, none of the patients with constipation were able to achieve this without the addition of weights which varied from 350 to 1150g. COLONIC TRANSIT STUDIES

Studies of total gut transit time may be made using the radioopaque shape technique of Hinton, Lennard Jones and Young (5). Twenty radio-opaque shapes, 2 x 3 mm, are taken by mouth on the morning of day 1 and a plain abdominal X-ray is taken 5 days later (Day 6). Patients are instructed to omit laxatives, suppositories or enemas the day prior to the study and during the study period. Normal subjects pass 80% of shapes, about 16, by 5 days and those who have more shapes remaining have slow intestinal transit. The shapes are clearly visible on X-ray and have a similar specific gravity to that of the stool. ELECTROPHYSIOLOGICAL TECHNIQUES

Conventional concentric EMG Floyd and Walls (6) investigated the external anal sphincter in man using surface electrodes which comprised 1 cm diameter silver/silver chloride discs which were applied to the perianal skin. Surface electrodes cause minimum interference to the muscle and are consequently readily tolerated by patients. The potentials recorded are summated from multiple muscle fibres. The electrical activity generated by the active contraction of nearby adductor and gluteal muscle groups may be indistinguishable from potentials arising from the external anal sphincter complex.

For these reasons we prefer to use bipolar concentric needle electrodes as the summation of potentials is limited to about 30 muscle fibres lying within the vicinity of the electrode tip and only these are recorded (7). The electrodes (Medelec EL75M) consist of an outer cannula 4 cm long, one end of which is pointed and bevelled to facilitate entry through the skin and an inner core of wire separated from the cannula by an insulating layer. The potential difference between the bare tip of the centre wire and the outer cannula over an area of 0.22 mm2 is recorded using this technique. Since the amplitude of the recorded potentials within the external anal sphincter and pelvic floor muscles is of the order 50 pV to 2 mV it is necessary to amplify the signals before display on an oscilloscope or before a permanant recording can be made. With the patient lying in the left lateral position a ground electrode is strapped to the uppermost thigh and the recordings are made in the resting state, during- voluntary contraction and during straining. The needle is inserted into the external anal sphincter without local anaesthetic. Additional recordings are sometimes made from the puborectalis muscle in which case the needle is guided into position from the perineal skin by digital palpation of the muscle in the upper posterior part of the anal canal. In the normal resting state continuous or 'basal' action potentials will be obtained in both muscles (6). This phenomenon is not usually displayed by skeletal muscle which is characteristically electrically silent at rest. It probably arises as a result of a spinal reflex (8). During voluntary contraction there is a burst of activity which is the consequence of increased frequency of motor unit firing and recruitment of new motor units. In contrast, during defaecation, reflex inhibition of electrical activity occurs, followed by brief periods of greatly increased activity at the completion of this act.

Contraction reflexly induced by balloon distension of the rectum or by perianal pinprick can also be recorded

electromyographically. Single fibre EMG The individual motor unit potentials recorded with a concentric needle electrode are generated by the muscle fibres of individual motor units (9). The amplitude and shape of the motor unit potential is determined by the number of muscle fibres within the recording area of the concentric needle electrode. Thus this method has limitations because little information is gained with respect to the individual elements generating the motor unit potential. As a result of these inadequacies the concept of single fibre EMG has been developed (9). This technique identifies the muscle action potential from a single muscle fibre by employing an electrode of 25 to 30 gm in diameter. The technique provides a means of assessing innervation and reinnervation of the skeletal muscle under investigation. The assessment can be made quantitatively using the fibre density which represents the mean of a number of muscle fibres supplied by one motor unit within the uptake area of the electrode averaged from 20 different electrode positions. If the fibre density is raised then this may be used as an index of collateral sprouting and reinnervation of muscle fibres within the muscle (Fig. 1). Collateral axonal sprouting and reinnervation of denervated muscle takes place from neighbouring healthy axons (10). The external anal sphincter behaves in the same way as other skeletal muscles in that its fibre density rises slightly after the age of 60 years, indicating that skeletal muscle becomes denervated as part of a normal aging process (11). The technique as we have applied it to the external anal sphincter involves the insertion of a Miller-Abbott balloon into the rectum, inflating it with 30 ml of air and applying traction of 150 g. Using this technique the rate of motor unit firing is increased thereby facilitating the identification of motor unit activity. This should be assessed in at least 20 differing sites in the external anal sphincter complex. In our laboratory a motor unit potential is only analysed if its rise

Investigation of disorders of the ano-rectum and colon

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FIG. 1 Oscilloscope tracing of single fibre EMG. Upper tracing: single muscle unit action potentials in the external anal sphincter in a normal subject. Lower tracing: patient with faecal incontinence. Note 4 action potentials consistent with reinnervation: at least 4 muscle fibres have been supplied by the same axon within the territory of the electrode tip.

time is faster than 300 mS and its amplitude is greater than 00 jV. The technique employs standard EMG equipment and single fibre electrodes, using a low frequency band pass filter of 500 Hz in the amplifier (9). It requires a moderate degree of practice before satisfactory results can be obtained. In our laboratory the mean value for fibre density in subjects younger than 65 years is 1.5+0.16 (SD), but in subjects younger than 30 years a lower value is obtained (1.32 ± 0. 1)

FIG. 3. The pudendal nerve glove stimulator. The stimulating cathode is at the tip, the recording electrodes are sited at the base.

NERVE STIMULATION TECHNIQUES

Spinal stimulation Transcutaneous electrical stimulation of the spinal cord was first achieved by Merton et al. (12). The patient lies in the left lateral position and a stimulus of 700 to 1000 V (duration 0.5 mS) is applied to the spine initially at the level of LI and repeated at the L4 level. The stimulus electrode comprises two 1 cm diameter gauze pads 5 cm apart. The pads are soaked in physiological saline and applied vertically across the spine; the cathode is placed caudally. The induced response within the pelvic floor can be detected either by a surface anal plug electrode or by an intramuscular needle electrode. The mean latency to the external anal sphincter is 5.5 mS + 0.4 (SD), and to the puborectalis.muscle.is 4.8+0.4 (SD) in the normal subject (13). We have found that it can be important to differentiate between the puborectalis and external anal sphincter since it appears that these muscles have separate innervations (14). The differing motor latencies to the two muscles following spinal stimulation supports this contention (Fig. 2). Pudendal nerve terminal motor latency The method we have employed for determining the pudendal nerve terminal motor latency was developed from the technique of electroejaculation for use in patients with impotence (15). The device consists of two stimulating electrodes situated at the tip of a rubber finger stall. Two recording surface electrodes

incorporated into its base (Fig. 3). The anode is 5 mm and the cathode less then 1 mm in diameter to improve the accuracy of stimulus localisation. The recording electrodes consist of two 1 cm diameter metal plates separated by 1 cm and are located side by side 3 cm from the cathode so that they are at the base of the examiner's finger when the device is in use. The patient lies in the left lateral position with a ground electrode strapped to the uppermost thigh. A rectal examination is performed with the finger stall and the tip containing the stimulating electrode is brought into contact with the ischial spine on each side. A square wave stimulus of 0.1 mS duration and 30 V amplitude is delivered. The oscilloscope tracing is examined for evidence of contraction, as detected in the external anal sphincter by the surface electrodes thereby indicating accurate localisation of the pudendal nerve. As soon as this has been achieved a supramaximal stimulus (usually of the order of 50V) is delivered and the latency measured on each side (Fig. 4). Using this technique the motor latency of the terminal portion of the nerve is 2.OmS±+0.2 (SD). Perineal nerve terminal motor latency A similar technique can be employed for determining the distal motor latency in the perineal branch of the pudendal nerve by measuring the are

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latency from pudendal nerve stimulation to the peri-urethral striated muscles. The response in this muscle is detected by surface electrodes mounted on a commercially available Foley catheter (DISA 21L 1). The normal perineal nerve terminal motor latency is 2.4mS+0.2 (SD)., reflecting the slightly longer length of this branch of the pudendal nerve from the point of stimulation (16). Clinical application ANORECTAL INCONTINENCE

The investigation of the faecally incontinent patient constitutes a major part of the workload of this unit. The studies described here can be used to identify the anatomical site of the lesion in some patients. In all patients they provide an objective means of assessing anal sphincter and pelvic floor function.

Manometry This is a simple and rapid means of assessing sphincter function and is widely used in units which deal with pelvic floor disorders. It is the only readily available technique which can provide an assessment of internal anal sphincter deficiency which may develop with third degree haemorrhoids or complete rectal prolapse, for example. As a means of assessing external anal sphincter and pelvic floor function it is less successful. The measurement of intra-anal pressures sustained during voluntary contraction requires a degree of co-operation which cannot always be guaranteed. Broadly speaking, most patients who are regularly incontinent of fully formed stools may demonstrate normal resting pressures but reduced contraction pressures. This indicates normal internal sphincter function and striated muscle weakness. Conventional EMG In patients with idiopathic faecal incontinence the usual finding is a marked reduction in interference pattern and in resting electrical activity. This is not readily quantifiable but is to a certain degree possible by analysis of the individual motor action potential (17). Conventional EMG is of greater importance in sphincter mapping in patients who have suffered traumatic division of the external anal sphihcter complex. Electromyographic exploration of the perineum may assist the identification of the retracted divided ends of the sphincter muscle. This information may be of vital importance to the surgeon when sphincter repair is contemplated. It is also useful in the preoperative assessment of children with rectal atresia who are being considered for a 'pull-through' procedure. Single fibre EMG This is a truly objective and quantitative means of assessing function and more especially for identifying denervation in the external anal sphincter and pelvic floor muscles. In the majority of patients with idiopathic faecal incontinence the fibre density is raised, consistent with

Investigation of disorders of the ano-rectum and colon

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reinnervation (18). Pelvic floor denervation is not confined to idiopathic faecal incontinence but may occur with certain generalised neurological disorders or be secondary to injury to the cauda equina. Trauma to the pelvic floor, such as occurs with a fractured pelvis, may also be associated with denervation of these muscles. A raised fibre density would suggest that a poor functional result might be the sequel of surgical repair of the anal sphincter in these patients. Nerve stimulation techniques These have been developed as a direct result of the histological evidence that idiopathic faecal incontinence was neurogenic in origin (19). Many of these patients show an increased pudendal nerve terminal motor latency so indicating a local damage to this portion of the nerve (20). Such damage may be the result of obstetric trauma (21) or be a stretch-induced injury in association with the 'descending perineum syndrome' (22). It is possible to investigate the central (cauda equina) component of the motor innervation of the pelvic floor by transcutaneous spinal stimulation. The latency of the motor unit action potential to the external anal sphincter (or puborectalis) following stimulation of the spinal cord at LI and L4 is compared to the pudendal nerve terminal motor latency. Our results indicate that faecal incontinence in some patients results from a central cause such as spinal stenosis (23). In these patients the difference in latencies from LI and L4 is considerably increased compared with control groups. In some patients the pudendal nerve terminal motor latency may be increased suggesting that a mixed lesion is responsible. Summary For routine purposes we find that the most useful index of neurogenic change in the somatic musculature of the anal sphincter is obtained by single fibre EMG. An objective assessment of fibre density is possible from which there is no overlap between the normal and denervated patients within stated age ranges. Spinal and pudendal nerve motor latency measurements enable the investigator to deduce the anatomical site of the lesion. Minor degrees of faecal incontinence may be the consequence of internal anal sphincter dysfunction and this will be diagnosed by manometric evaluation of resting anal tone. DESCENDING PERINEUM SYNDROME AND SOLITARY RECTAL ULCER SYNDROME

There is an ill-defined group of patients with pelvic floor disorders which may be worthy of study largely for the detection of the denervation changes in the pelvic floor muscles to which they are prone (22). This may be of considerable clinical significance since anal dilatation may render these patients incontinent (24). CONSTIPATION

The measurement of intestinal transit may be helpful in identifying the patient with slow transit who might benefit from colectomy and ileo-rectal anastomosis. Although constipation has long been ascribed to a disorder of colonic contractility, recent studies suggest that there may be a disorder of the normal defaecatory mechanism in many of these patients (3,4). A rare group of adult patients with constipation are found on radiological study to have evidence of a megarectum and megacolon. A small number of these have adult Hirschsprung's disease. The normal rectosphincteric inhibitory reflex is absent in patients with Hirschsprung's disease (25) and this thereby provides a simple and safe means of establishing the diagnosis. In a proportion of patients with megarectum the reflex is either difficult to elicit or is absent because of technical difficulties in distending the rectum or because of low resting sphincter tone.

Conclusions Many of the techniques described here have been devised initially for research purposes. They have gradually become integrated in our laboratory as routine investigations in the

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evaluation of patients with pelvic floor disease. The identification of the patient with a central cauda equina lesion may be important since myelography and a neurosurgical referral may be of greater immediate importance than surgery to the pelvic floor. All of the tests described here are safe and free of complications. The degree of discomfort caused to the patient is of a minimal nature.

References I Bennett RC, Duthie HL. The functional importance of the internal anal sphincter. Br J Surg 1964;51:355-7. 2 Denny-Brown D, Robertson EG. An investigation of the nervous control of defaecation. Brain 1835;58:256-310. 3 Preston DM, Lennard-Jones JE, Thomas BM. The balloon proctogram. Br J Surg 1984;71:29-32. 4 Preston DM, Lennard-Jones JE. Anismus in chronic constipation. Dig Dis Sci (in press). 5 Hinton JM, Lennard-Jones JE, Young AC. A new method for studying gut transit times using radio-opaque markers. Gut 1969; 10:842-7. 6 Floyd WD, Walls EW. Electromyography of the sphincter ani externus in man. J Physiol 1953; 122:599-609. 7 Buchthal F. The general concept of the motor unit. Res Publ Ass Nerv Ment Dis 1960;38:3. 8 Parks AG, Porter NH, Melzak J. Experimental study of the reflex mechanism controlling the muscles of the pelvic floor. Dis Colon Rectum 1962;5:407-414. 9 Stalberg E, Tronteli JV. Single fibre electromyography. Old Woking: Miralle Press 1979;64. 10 Stalberg E, Thiele B. Motor unit fibre density in the extensor digitorum communis muscle. J Neurol Neurosurg Psychiatry 1975;38:874-80. 11 Neill ME, Swash M. Increased motor unit fibre density in the external anal sphincter muscle in ano-rectal incontinence; a single fibre EMG study. J Neurol Neurosurg Psychiatry 1980;43:343-7.

12 Merton PA, Hill DK, Morton HB, Marden CD. Scope of a technique for electrical stimulation of human brain, spinal cord and muscle. Lancet 1 982;ii:597-600. 13 Snooks SJ, Swash M, Henry MM. Abnormalities in central and peripheral nerve conduction in patients with anorectal incontinence. J R Soc Med 1985;78:294-300. 14 Percy JP, Neill ME, Swash M, Parks AG. Electrophysiological study of motor nerve supply of pelvic floor. Lancet 1981;1: 16-7, 15 Bridley GS. Electroejaculation: its technique, neurological implications and uses. Neurol Neurosurg Psychiatry 1981;44: 9-18. 16 Snooks SJ, Swash M. Perineal nerve and transcutaneous spinal stimulation: new methods for investigation of the urethral striated sphincter musculature. Br J Urol 1984;56:406-9. 17 Bartolo DCC, Jarratt JA, Read MG, Donnelly TC, Read NW. The role of partial denervation of the puborectalis in idiopathic faecal incontinence. Br J Surg 1983;70:664-7. 18 Neill ME, Parks AG, Swash M. Physiological studies of the pelvic floor in idiopathic faecal incontinence and rectal prolapse. Br J Surg 1981;68:531-6. 19 Parks AG, Swash M, Urich H. Sphincter denervation in anorectal incontinence and rectal prolapse. Gut 1977; 18:656-65. 20 Kiff ES, Swash M. Slowed conduction in the pudendal nerves in idiopathic (neurogenic) faecal incontinence. Br J Surg 1984;71: 614-6. 21 Snooks SJ, Setchell M, Swash M, Henry MM. Injury to innervation of pelvic floor sphincter musculature in childbirth. Lancet 1984;ii:546-50. 22 Henry MM, Parks AG, Swash M. The pelvic floor musculature in the descending perineum syndrome. BrJ Surg 1982;69:470-2. 23 Snooks SJ, Swash M. The application of translumbar spinal stimulation in the investigation of patients with suspected cauda equina lesions. Brain (in press). 24 Snooks SJ, Henry MM, Swash M. Faecal incontinence after anal dilatation. Br J Surg 1984;71:617-19. 25 Lawson JON, Nixon HH. Anal canal pressures in the diagnosis of Hirschsprung's disease. Paed Surg 1967;2:544-52.