Physiological Approach James W, Lance M.D., M.R.C.P., F.R.A.C.P. By the same author The Mechanism and Management of Headache to Clinical Neurology Chairman, Division of Neurology, Prince Henry and Prince of Wales Hospitals; Associate Professor of Medicine, University of New South Wales, Sydney, Australia London: Butterworths ENGLAND: BUTTERWORTH & CO. (PUBLISHERS) LTD. LONDON: 88 Kingsway, W.C.2 AUSTRALIA: BUTTERWORTH & CO. (AUSTRALIA) LTD. SYDNEY: 20 Loftus Street MELBOURNE: 343 Little Collins Street BRISBANE: 240 Queen Street CANADA: BUTTERWORTH & CO. (CANADA) LTD. TORONTO: 14 Curity Avenue, 374 NEW ZEALAND: BUTTERWORTH & CO. (NEW ZEALAND) LTD. WELLINGTON: 49/51 Bal lance Street AUCKLAND: 35 High Street SOUTH AFRICA: BUTTERWORTH & CO. (SOUTH AFRICA) LTD. DURBAN: 33/35 Beach Grove © Mrs J. L. Lance 1970 Suggested U.D.C. No. 612-8:616-8 ISBN 0 407 35850 1 Printed in Great Britain by R. J. Acford Ltd., Industrial Estate, Chichester, Sussex To Professor P. O. Bishop who must assume some responsibiUty for my becoming a neurologist Preface As a clinical neurologist and amateur physiologist, I have always sought to bridge the gap between the research laboratory and the hospital ward in teaching undergraduate and postgraduate students. A knowledge of neuroanatomy and neuropathology is generally accepted as a basis for the understanding of clinical neurology, while neurophysiology has become isolated in the student's mind by its technology, its emphasis on animal experimentation, and its apparent lack of relevance to clinical problems. The account given here attempts to overcome this unhappy state by explaining the mechanism of various neurological symptoms and signs in terms of disordered physiology wherever this is possible. To present a simple version of complex and often controversial mechanisms and then to illustrate the concept by line diagrams is to invite criticism, but this has been done deliberately since the value of an interpretation lies in its clarity as well as its validity. The validity of the text will certainly change with the acquisition of new experi­ mental evidence and re-examination of the old. Thus, no statement in the following pages can be regarded as immutable. The coverage is patchy, reflecting the interests and bias of the author, since there is no intention to compete with comprehensive textbooks of neuro­ physiology or clinical neurology. The first two chapters are designed as an introduction to the clinical analysis of sensory and motor disorders. In the later chapters, appraisal of current neurophysiological thought is applied to common neurological syndromes. The author hopes that the presentation will be clear enough to hold the interest of the clinical reader, without being so artless as to offend the professional physiologist. The book is proffered to those who are proceeding into the clinical years of a ix PREFACE medical course, to those who are studying for senior qualifications in internal medicine or neurology, and to those who are merely curious about the cause of neurological phenomena which they observe daily in their patients. However brilliant the physiological advances made in the understanding of other species, they are profit­ less for man until applied to him. JAMES W. LANCE Acknowledgements I am indebted to Professor P. O. Bishop and Dr. J. G. McLeod for their helpful criticism of the text which has reduced, if not eliminated, its inadequacies. The continuation of the research programme into tonic and phasic stretch reflexes in man has only been possible through the assistance of Dr. J. D. Giflies, Dr. P. de Gail, Dr. C. A. Tassinari, Dr. D. Burke and Mr. P. D. Neilson, and financial support from the National Health and Medical Research Council of Australia, the Adolph Basser Foundation, Sandoz (Australia) Ltd. and Ciba Co. Pty. Ltd. The preparation of the text owes much to my secretary, Mrs. R. M. Kendall, who has cheerfully added this task to her normal duties. Miss J. B. Pate, librarian, has kindly obtained all references for me. The line diagrams were drawn by Mrs. G. Lindley from my primitive sketches, and all photographs and figures were prepared by the Department of Medical Illustration, University of New South Wales. I am grateful to the editors of Brain, Journal of Neurology, Neuro­ surgery and Psychiatry and the Medical Journal of Australia for permission to use material and figures from earlier publications. I wish to thank those authors whose illustrations I have used as models, where acknowledged in the legends. 1—Pain and other Sensations The nervous system of a normal individual is constantly active in conveying information to the brain about the state of the body and of the world outside it. If all these neuronal messages were received in equal measure, consciousness would become a nightmare of confused and largely irrelevant stimuli, so that a selective response would become impossible. Fortunately, there are various physio­ logical processes which speed the passage of pertinent stimuli and retard awareness of the background activity. We thus become oblivious to the touch of clothes, the pressure of a hard seat and the functioning of contented viscera. The processes involved in this selectivity of sensations are as follows. (1) Adaptation of sensory end organs, which cease to respond after variable periods of stimulation. (2) Presynaptic inhibition of adjacent nerve cells by collaterals from an active nerve cell, thus assuring priority for 'the stimulus of the moment'^. This process probably takes place at all levels of the nervous system, thus repeatedly 'refining' the impulses representing a particular sensation, or, in electronic jargon, ensuring 'a high signal-to-noise ratio'. (3) Regulation of synaptic transmission in sensory nuclei by the motor cortex. Stimulation of the sensorimotor cortex of the cat may inhibit or excite nerve cells in the cunéate and gracile nuclei by means of collaterals from the pyramidal tract and, to a lesser extent, by an extrapyramidal system^'This provides a mechanism for the voluntary suppression of sensory information or for involuntary suppression during movement. (4) Alteration in the state of awareness at a cortical level in that a subject while fully conscious, may so concentrate his 1 PAIN AND OTHER SENSATIONS attention on a particular sensation, thought or response as to preclude perception of other sensations. The perception of any sensation therefore depends not only on the appropriate receptor organ in skin, muscle, joint or viscus, and the integrity of the peripheral nerve and spinal cord pathways, but also on complex connexions within the cerebral cortex which may be influenced by the thoughts and emotions of the subject. Thus sensa­ tion is subjective and each individual has his own 'perceptual world' which is unique to him and can be known to others solely by his description of it. A certain stimulus may be registered by some as pleasant, by others as unpleasant but tolerable, and by others as so uncomfortable that they use the term 'pain' to describe it. Each person may therefore be regarded as having a 'pain threshold', and if the level of sensory stimulation exceeds this, pain is experienced. When the normal functioning of the body is disturbed, sensory impulses of unusual quantity, quahty or pattern are received by the brain, and the resulting 'sense data' are expressed by the subject as 'symptoms'. Sensory symptoms Symptoms bring the patient to the doctor. It is part of the art of medicine to record the patient's symptoms accurately and to interpret them in the light of the patient's intellectual and educational endow­ ment, his personality and his emotional state. Symptoms may be negative in that the patient complains of numbness or inability to feel touch, pain, temperature or position of the limbs. Symptoms may also be positive, providing curious abnormal sensory experiences. Ischaemia or irritation of peripheral nerves or the central projec­ tion of touch pathways gives rise to the prickling sensation described as 'pins and needles' or the arm or leg 'going to sleep'. Compression of the lateral cutaneous nerve of the thigh in the inguinal ligament produces a curious creeping feeling in the outer aspect of the lower thigh which has been likened to the sensation of ants crawling under the skin (formication). A disturbance within the posterior root entry zone or posterior columns of the spinal cord, or pressure upon them, may be responsible for a girdle sensation around the trunk, described as a tight band; or a feeling of pressure in the limbs as though they were being wrapped by a bandage. Sudden flexion of the neck may induce an electric shock sensation which shoots down the back when there is a cervical lesion irritating the posterior columns. This phenomenon (Lhermitte's sign) is found most commonly in cervical spondylosis THE PERCEPTION OF DIFFERENT KINDS OF SENSATION and multiple sclerosis. A lesion in the spinothalamic tracts or thalamus produces an unpleasant burning sensation or pain which spreads diffusely down the opposite side of the body. Irritation of the sensory cortex evokes paraesthesiae, which may spread rapidly over the contralateral side as an epileptic phenomenon, or advance more slowly when caused by migrainous vasospasm. The sensory association areas in the parietal lobe may give rise to weird illusions of the body image so that parts of the body appear larger or smaller than normal. Pain is the most consistently unpleasant symptom which the nervous system can provide and may signal a disorder in any part of the body through irritation or distortion of sensory endorgans, or may arise from disease of the sensory pathways at any level from endorgan to cortex. Pain is often associated with an emotional change so that it may be hard to determine which is primary and which secondary. In spite of all the complexities of the individual reaction to pain, it is usually possible to analyse the description of the pain so as to determine its site of origin and often its cause. THE PERCEPTION OF DIFFERENT KINDS OF SENSATION: SEGREGATION OR INTEGRATION OF NEURAL PATHWAYS? There is still controversy between those who believe that there are specific endorgans and nerve fibres for each modality of sensation, and those who believe that it is the pattern of impulses in any nerve which determines the type of sensation. The encapsulated end- organs which may serve a specialized function (touch, pressure, heat, cold) are concentrated in areas of the body which are particularly sensitive—the tips of the fingers, the lips, the areola of the breast and the genitalia. It is probable that all these endorgans may give rise to the sensation of pain if the stimulus is excessive. The free nerve endings which are found in profusion in all areas of skin are probably the chief pain receptors under normal circumstances, but it has been shown by Lele and Weddell^^ that even these may perceive sensations of touch, heat and cold as well. Melzack and Wall^^ have put forward a hypothesis which attempts to unify the two conflicting concepts of sensibility. They point out that skin receptors are transducers which may respond to more than one type of environmental energy, and that the sequence of nerve impulses produced by the receptor is the function of a number of