Peripheral Neuropathy & Neuropathic Pain

Into the Light

Professor Gérard Said MD FRCP

• Publisher: tfm Publishing Ltd
• Year: 2014
• ISBN:
  9781910079003
• Topic: Medicina
• Subtopic: Neurología

Written by one of the world's leading experts — Professor Gérard Said MD FRCP, Dpt de Neurologie, Hôpital de la Salpêtrière, Paris, FrancePeripheral neuropathy is a common medical condition, the diagnosis of which is often protracted or delayed. It is not always easy to relate a neuropathy to a specific cause. Many people do not receive a full diagnosis, their neuropathy often being described as 'idiopathic' or 'cryptogenic'. It is said that in Europe, one of the most common causes is diabetes mellitus but there are also many other known potential causes. The difficulty of diagnosis, the limited number of treatment options, a perceived lack of knowledge of the subject —except in specialised clinics, the number of which are limited — all add to the difficulties which many neuropathy patients have to face. Another additional problem for many patients is that once having received a full, or even a partial diagnosis, they are then often discharged back to their primary healthcare team who, in many instances, know little about this condition and how it may impact upon their patients' lives.In order to help bridge this gap in medical knowledge and to give healthcare providers a better understanding of this often distressing condition, The Neuropathy Trust has commissioned a new book on this complex topic. Written by one of the world's leading experts on neuropathy, Professor Gérard Said, it is a 'must read' and also a handy reference book for doctors, nurses, physiotherapists, chiropodists/podiatrists and other health professionals.As well as covering the anatomy of the nervous system and the basic pathological processes that may affect the peripheral nerves, the book covers a whole range of neuropathic conditions. These include, for example, Guillain-Barré syndrome, chronic inflammatory demyelinating polyneuropathy, vasculitic neuropathies, infectious neuropathies, diabetic and other metabolic neuropathies, hereditary neuropathies and neuropathies in patients with cancer. Given the almost explosive increase in diabetes predicted over the coming years and the high incidence of HIV infections alone, not to mention all the other possible causes of peripheral neuropathy, no self-respecting medical unit should be without a copy of this new book on their shelves.The author, Professor Gérard Said, is based in the Department of Neurology at the prestigious Hôpital de la Salpêtrière in Paris. He has devoted a lifetime to the study of peripheral neuropathy and — alongside other great neurological names — added much to the world's ever-growing store of knowledge on this complex but fascinating condition which affects so many individuals.

Chapter 1

Anatomy of the peripheral nervous system

Overview

This chapter is about the different components and functions of the peripheral nervous system which links the central nervous system (brain and spinal cord) to muscles and to sensory receptors for activation of muscle contraction and perception of sensation. The anatomy, motor and sensory territories supplied by plexuses and nerve trunks, and cranial nerves are detailed. The anatomy and function of the sympathetic and parasympathetic nervous systems are also outlined. Microscopic anatomy details the morphology and role of myelinated and unmyelinated nerve fibres.

Introduction

The peripheral nervous system (PNS) has two components: the somatic peripheral nervous system which includes sensory and motor neurons and nerve fibres, and the autonomic nervous system which comprises the sympathetic and parasympathetic systems¹. The somatic peripheral nervous system controls muscle contraction and perception of sensation, while the autonomic nervous system works automatically without conscious control.

Somatic peripheral nervous system

Each spinal nerve results from the fusion of two roots. The ventral root is formed by the aggregation of spinal motor rootlets (motor neuron axons). The cell body, or perikaryon, of the motor fibre is located in the anterior horn of the spinal cord. The dorsal root contains the dorsal root ganglion, where cell bodies of all sensory neurons of the PNS are found. These two roots unite to form the mixed spinal nerve. There are eight pairs of cervical spinal nerves, twelve pairs of thoracic spinal nerves, five pairs of lumbar spinal nerves, five pairs of sacral spinal nerves and a few pairs of coccygeal nerves.

Cervical plexus

The motor fibre endings of the cervical plexus innervate cervical muscles and the diaphragm. Sympathetic sudomotor and vasomotor fibres pass through this plexus to blood vessels and glands.

Brachial plexus

The brachial plexus is formed by the assembly of C5, C6, C7, C8 and T1 ventral roots. Three trunks (superior, middle and inferior) originate from the brachial plexus. Each of these trunks divides into a ventral and a dorsal branch and three cords are formed (lateral, posterior and medial), which finally lead to the spinal nerves of the upper limbs. The superior brachial plexus is very vulnerable during birth trauma with subsequent deltoid, biceps, brachialis and brachioradialis paralysis. Lower plexus compression by a cervical rib (C8, T1), or infiltration by cells originating from a breast or pulmonary cancer, may cause paralysis of the small hand muscles.

Nerves of the upper limbs

The nerves of the upper limbs are as follows:

•the musculocutaneous nerve (C5, C6) innervates muscles predominantly involved in flexion of the arm;

•the scapular nerve (C5) innervates muscles for elevation and adduction of the scapula;

•the suprascapular nerve (C5-C6) innervates the supraspinatus and infraspinatus muscles for lift and outward rotation of the arm, resulting in abduction of 15° and external rotation of the arm;

•the axillary nerve (C5-C6) innervates the deltoid and teres minor muscles for abduction of the arm to the horizontal and outward rotation of the arm;

•the radial nerve (C6-C8) innervates the triceps, anconeus, brachioradialis, extensor carpi radialis, extensor digitorum and supinator muscles for extension and flexion of the elbow and supination of the forearm; muscles for the extension and flexion of the elbow, supination of the forearm, extension of the wrist and fingers, and abduction of the thumb. Sensory innervation is to the posterior upper arm and forearm, and the posterior thumb and lateral 2½ fingers;

•the median nerve (C5-T1) innervates muscles involved in flexion of the fingers, abduction and opposition of the thumb, and pronation of the forearm. Sensory innnervation is to the palm and fingers 1 to 3 and the lateral half of the fourth finger;

•the ulnar nerve (C8-T1) innervates muscles controlling abduction and adduction of the fingers and wrist flexion; sensory innervation supplies the dorsal and palmar medial faces of the hand, and half of fingers 4 and 5.

Thoracic nerves

The 12 pairs of thoracic nerves give rise to the cutaneous innervation of the thoracic dermatomes. Motor fibres supply innervation of the muscles of the thoracic and abdominal walls.

Lumbosacral plexus

The lumbar plexus is composed of primary branches of the anterior roots L1, L2, L3 and L4. Iliogastric, ilioinguinal and genitofemoral nerves originate from the L1 root and innervate transverse and oblique abdominal muscles. Femoral, obturator and lateral femoral cutaneous nerves are formed from the remaining roots. These nerves are responsible for flexion and adduction of the thigh, leg extension, and sensory innervation of the anterior thigh and leg.

The sacral and coccygeal plexuses are formed from roots coming from L4 to S4. Their main terminal branches are the superior (L4-S1) and inferior gluteal nerves (L5-S2), the posterior femoral cutaneous nerve (S1-S3), the sciatic nerve (L4-S3) and its division into the tibial and common peroneal nerves, and to the pudendal nerve. They result in extension of the thigh, leg and foot, and help to close the bladder and rectal sphincters, and supply sensory innervation of the thigh and perianal region.

Nerves of the lower limbs

The nerves of the lower limbs are as follows:

•the femoral nerve (L2-L4) motor fibres supply the iliopsoas, sartorius and quadriceps femorus muscles resulting in flexion and outward rotation of the lower leg and extension of the lower leg over the thigh; sensory innervation is to the anterior thigh and anterior and medial surfaces of the leg and foot;

•the lateral femoral cutaneous nerve is purely sensory and innervates the anterior and lateral surfaces of the thigh;

•the obturator nerve (L2-L4) controls adduction and rotation of the thigh; cutaneous innervation is on the internal thigh;

•the superior gluteal nerve (L4-S1) controls abduction and inward rotation of the thigh and flexion of the upper leg to the hip;

•the inferior gluteal nerve (L4-S1) motor fibres command extension of the thigh at the hip and outward rotation of the thigh;

•the sciatic nerve (L4-S3) motor fibres supply the biceps femoris, semitendinosus and semimembranosus muscles resulting in flexion of the lower leg, and also muscles dependent upon the tibial and peroneal branches that are terminal branches of the sciatic nerve;

•the posterior femoral cutaneous nerve (S1-S3) supplies sensory innervation of the posterior thigh, lateral perineum and lower buttock;

•the tibial nerve (L4-S2) motor fibres control plantar flexion, inve...