Electrodiagnostic studies comprising of electromyography (EMG) and nerve

Transcription

1 INTRODUCTION AND TERMINOLOGY Electrodiagnostic studies comprising of electromyography (EMG) and nerve conduction studies (NCS) are well-established objective methods for the diagnosis, quantification and classification of poly neuropathies (PNP) 1,2,3,4,5 NCS along with EMG have an important role in the evaluations of peripheral neuropathies such as the clinical confirmation of neuropathy, identifying the pathophysiology such as axonal or demyelinating, sensory, motor, or mixed, chronology and temporal course of the 1,2, 3,4,5. disease like, acute, subacute or chronic, etc. The clinical electro diagnosis involves the recording, display, measurement, and interpretation of action potentials arising from central nervous system (evoked potentials), peripheral nerves (nerve conduction studies) and muscles (electromyography). There are various principles that are followed whilst carrying out nerve conduction studies (NCS). A number of physiological and technical variables can influence the results of NCS 1,2 viz. age, temperature, instrumentation errors, etc. These studies can be carried out on commercially available machines which have user friendly programs. The routine electro diagnostic evaluation includes sensory NCSs performed with surface or needle electrodes, motor NCSs, F-wave studies, H-reflex and EMG by qualitative or quantitative techniques. 1

2 HISTORY OF F-WAVE The F wave is a late response resulting from antidromic stimulation of motor neurons involving conduction to and from spinal cord and occurs at the interface between the peripheral and central nervous system. 2, 6, 7 The name F wave is attributed to their recognition for the first time in the small muscles of the foot and hand by Magladery and McDougal in ,2,7,8 The antidromic origin of F waves has been confirmed by their presence in deafferented man as well as by single fibre analysis indicating that F requires direct activation of motor neurons unlike H- reflex. 1,2,6,7 The H- reflex is also a late response, described by Hoffman in 1918 and hence its name. The H-reflex is a monosynaptic reflex elicited by sub maximal stimulus. Both H reflex and F responses differ in their genesis, but are known as late responses because they are the potentials appearing after motor response (M wave). 8 F waves are most prominent and easily elicited at supra maximal stimulation (25% above the maximal). The difference between the H-reflex and F- response is as shown below: 2, 8 Parameters H reflex F wave Nature Monosynaptic reflex Antidromic stimulation of α motor neuron Afferent 1 α fiber α motor fiber Efferent α motor fiber α motor fiber Best elicited in Soleus, flexor carpi Any distal muslces Radialis, vastus medialis 2

3 Stimulus Submaximal Supramaximal Increasing stimulus Inhibit Facilitate Amplitude % of M wave 5% of M wave Morphology Stable Variable Motor unit in M Different Same Persistence Persistent Variable Useful in Neuropathy, radiculopathy, Neuropathy, Spasticity Radiculopathy MECHANISM OF ELICITING F-WAVE In a typical F wave study, a strong electrical stimulus (supra maximal stimulation) is applied to the skin surface above the distal portion of a nerve so that the impulse travels both distally (towards the muscle fiber) and proximally (back to the motor neurons of the spinal cord) as shown in figure. 3

4 FIGURE Mechanism of F- wave (These directions are also known as orthodromic and antidromic, respectively.) When the orthodromic stimulus reaches the muscle fiber, it elicits a strong M wave indicative of muscle contraction. When the antidromic stimulus reaches the motor neuron cell bodies, a small portion of the motor neurons backfire and orthodromic wave travels back down the nerve towards the muscle. This reflected stimulus evokes small proportion of the muscle fibers causing a small, second CMAP called the F wave. The name F wave was derived for the first time in the intrinsic muscles of foot by Magladery and McDougal in The afferent and efferent for F waves are alpha motor neurons. They are produced at the supramaximal stimulus unlike H reflex. 2,8,9 4

5 MORPHOLOGY The morphology is variable whereas in H reflex it is consistent throughout. F waves are irregular in appearance; low in amplitude; and inherently variable in latency, amplitude, and configuration. Meaningful analysis of F-waves requires allowance for these features of F-waves as well as an understanding of their physiology. 6 Despite these complexities, F-waves are one of the basic studies in clinical neurophysiology and provide clinically useful information in patients with disorders of the peripheral and central nervous system. 4,5,6,8,9 Cai F, Zhang J. 10 reported that, at age 3 years, the normal values were in the adult range for all motor conduction velocities and for the sensory conduction velocities in the upper limbs. The sensory conduction velocities, H-reflex velocities, and F-wave velocities in the lower limbs did not reach adult values until age 6 years whereas the upper limb F-wave velocities reached adult levels between 6 and 14 years in different nerves. These results indicate that adult values for nerve conduction velocities, including the late responses, are reached earlier in the lower extremities; however, conduction velocities at any age are always faster in the upper limbs and in the proximal compared to the distal segments. The maturation process occurs most rapidly during the first 3 to 6 years of life, especially in the first year. This parallels the histologic development of peripheral nerves during childhood. Conduction velocity estimated from the minimum and maximum latencies of F waves evoked by several stimuli are generally assumed to represent the range of motor axon conduction velocities for that nerve. 1,2,6 This approach provides general information about impulse conduction in the entire nerve. It does not reveal the conduction characteristics of specific axons. 5

6 USES OF F- WAVES There are number of uses of F- waves in clinical practice, the commonly employed parameters are F-wave minimum latency, persistence, chrono dispersion, amplitude, and repeater waves. The F waves provide useful information about the pathologies of central and peripheral nervous system however the changes in F wave should be interpreted in the clinical context. 1, 2,4,5,6,8,9 We commonly see patients of diabetic neuropathy and Guillian Barre syndrome referred for electro diagnosis, it would be highly useful to study in details the patho physiology leading to changes of the pattern of F- responses in these two common conditions. POLY NEUROPATHY The terms "poly neuropathy," "peripheral neuropathy," and "neuropathy" are frequently used interchangeably, but are distinct. Poly neuropathy is a specific term that refers to a generalized, relatively homogeneous process affecting many peripheral nerves, with the distal nerves usually affected most prominently. Peripheral neuropathy is a less precise term that is frequently used synonymously with poly neuropathy, but can also refer to any disorder of the peripheral nervous system including radiculopathies and mononeuropathies. Neuropathy, which again is frequently used synonymously with peripheral neuropathy and/or poly neuropathy, can refer even more generally to disorders of the central and peripheral nervous system. More than 100 types of peripheral neuropathy have been identified, each with its own characteristic set of symptoms, pattern of development, and prognosis. Sensory nerves perceive sensations such as pain or pleasure; motor nerves connect to muscles and send signals that cause movement; and autonomic nerves control many unconscious processes, such as heart rate, blood pressure, bladder control and digestion. Poly 6

7 neuropathy can cause many different symptoms depending on which types of nerves are damaged 11,12,13,14,15 The longest nerves in the body reach to the feet and hands, and these nerves are often the first to become damaged in cases of poly neuropathy, explains the National Institute of Neurological Disorders and Stroke. The symptoms often begin with loss of sensation, numbness, tingling, or burning in the hands and feet, which spread up the arms and legs over time. As the condition progresses, the pain may intensify into sharp bolts of pain like electric shocks. The hands and feet may lose the ability to sense touch or temperature, meaning that cuts and burns may go unnoticed. In other cases, the hands and feet may become over-sensitive to touch, such that light touches cause severe pain. Sensory nerve damage causes a more complex range of symptoms because sensory nerves have a wider, more highly specialized range of functions. Larger sensory fibers enclosed in myelin register vibration, light touch, and position sense. Damage to large sensory fibers lessens the ability to feel vibrations and touch, resulting in a general sense of numbness, especially in the hands and feet. People may feel as if they are wearing gloves and stockings even when they are not. Many patients cannot recognize by touch alone the shapes of small objects or distinguish between different shapes. This damage to sensory fibers may contribute to the loss of reflexes (as can motor nerve damage). Loss of position sense often makes people unable to coordinate complex movements like walking or fastening buttons, or to maintain their balance when their eyes are shut. Neuropathic pain is difficult to control and can seriously affect emotional well-being and overall quality of life. Neuropathic pain is often worse 7

8 at night, seriously disrupting sleep and adding to the emotional burden of sensory nerve damage. Smaller sensory fibers without myelin sheaths transmit pain and temperature sensations. Damage to these fibers can interfere with the ability to feel pain or changes in temperature. People may fail to sense that they have been injured from a cut or that a wound is becoming infected. Others may not detect pains that warn of impending heart attack or other acute conditions. (Loss of pain sensation is a particularly serious problem for people with diabetes, contributing to the high rate of lower limb amputations among this population.) Pain receptors in the skin can also become over sensitized, so that people may feel severe pain (allodynia) from stimuli that are normally painless (for example, some may experience pain from bed sheets draped lightly over the body). If the motor nerves are damaged, many physical symptoms may develop, such as muscle weakness, loss of reflexes, fatigue and muscle twitching, fasciculation s or cramping. People with severe poly neuropathy may have difficulty standing or coordinating arm movements, and muscle mass may decrease greatly. Some patients suffer complete paralysis of one or more body parts, such as the arms, legs or even the face. Speech may become impaired, as well as the ability to swallow. Patients with poly neuropathy may develop problems controlling the bowel or bladder, such as constipation, diarrhea, and urinary incontinence, difficulty starting urination or a sensation of an incompletely empty bladder. Changes in blood pressure may occur, leading to dizziness, lightheadedness and fainting. The body may lose the ability to sweat properly, which can result in problems of heat intolerance. Poly neuropathy may 8

9 become life-threatening if the nerves controlling breathing or the heart beat become damage and cease functioning properly. Sensori motor poly neuropathy is a body-wide (systemic) process that damages nerve cells, nerve fibers (axons), and nerve coverings (myelin sheath). Damage to the covering of the nerve cell causes nerve signals to slow down. Damage to the nerve 11,12, 13,14,15, 16 fiber or entire nerve cell can make the nerve stop working. Peripheral Neuropathy is probably overlooked as the cause of falls in geriatric population. 17 PREVALENCE C N Martyn, R A C Hughes (1997) 14 state four per cent of diabetic patients developed peripheral neuropathy within five years of diagnosis. By 20 years after diagnosis, the prevalence had risen to 15%. Distal symmetric sensory neuropathy predominated. Many surveys, both population based and of clinical case series, have shown that these rates are probably underestimates. A large registry based study of insulin dependent diabetic patients found an overall prevalence of distal symmetric poly neuropathy of 34%, which rose to 58% in people 30 years of age and older. A study of non-insulin dependent diabetic patients, using criteria in which decreased or absent thermal sensation replaced sensory or motor signs, reported a prevalence of 26%. 14 A report, National Health and Nutrition Examination Survey (NHANES), of 2,873 men and women ages 40 or older (419 with diabetes), found a Poly Neuropathy prevalence of 14.8 percent. PN was defined as at least one insensitive area on the foot with, monofilament testing; it was also assessed by self-reported symptoms. The incidence of PN was significantly higher (62%) in the subset with 9

10 diabetes. The incidence of PN also increased significantly with age. NHANES found 8.1 percent of the year age group had PN, compared to 34.7 percent of individuals over age The overall incidence of peripheral neuropathy is 2.4% however, it increases to 8% in individuals aged above 55 years, and these figures do not include traumatic peripheral 14, 15, 18, 19 neuropathies. Guillain-Barre syndrome (GBS) has been the subject of over 30 population studies during the past 50 years, most of which have shown an annual incidence in the range 1 to 2 per population. The condition seems to be reasonably evenly distributed throughout the world and incidence rates are probably fairly stable over time. The annual incidence seemed to rise from 1-2 per in to 2-7 per in in Olmsted county, Rochester, USA.27 Similarly the annual incidence rose from about 1-3 per in the triennium to 2-7 per in when surveyed in Ferrara, northern Italy. 14 TYPES OF PERIPHERAL NEUROPATHY Acquired Neuropathies Immune-mediated (GBS, CIDP, vasculitis associated with CVD) Drugs or toxins Infectious (Lyme, HIV) Dysmetabolic states (DM, hypothyroid, uremia, Vit B12 deficit) Cancer related (paraneoplastic, direct infilteration) Mechanical(radiculopathy, mononeuropathy) Cryptogenic 10

11 Hereditary Neuropathies Hereditary motor & sensory (HMSN) Hereditary neuropathy with liability to pressure palsies (HNPP) Hereditary sensory & autonomic (HSAN) Familial amyloidosis Porphyria Other rare (Refsum s, Fabry s) Peripheral Neuropathies with Cranial nerveinvolvement* Guillain-Barre syndrome, CIDP Lyme disease Sarcoidosis Porphyria Certain forms of familial amyloid *Primarily the seventh nerve Idiopathic- Typically, idiopathic peripheral neuropathy occurs in people over 60 years old; progresses slowly (or doesn't progress at all after the initial onset); and it can be very disruptive to someone's normal life and lifestyle. THE 9 PATTERNS OF NEUROPATHY 1. Symmetric prox & distal weak w/sensory loss. 2. Symmetric distal weakness with sensory loss. 3. Asymmetric distal weakness with sensory loss. 4. Asymmetric distal weakness w/o sensory loss. 5. Asym. prox & distal weakness w/ sensory loss. 6. Symmetric sensory loss w/o weakness. 7. Symmetric sensory loss & distal areflexia with UMN 11

12 8. Asym. proprioceptive sensory loss w/o weakness. 9. Autonomic symptoms and signs. NR Rosenberg et al classified by electrophysiological findings whether the patient belonged to one of the following categories: 22 Category 1: uniform demyelinating neuropathy Category 2: non-uniform demyelinating neuropathy Category 3: pure motor axonal neuropathy Category 4: pure sensory axonal neuropathy Category 5: sensorimotor axonal neuropathy The precise incidence of each subtype of GBS has not been elucidated. The frequency of GBS subtypes varies considerably with geography. In Europe and North America, 90% of GBS cases are AIDP. In contrast, 60% to 80% of reported GBS cases were classified as being of the AMAN type in northern China. In a series of 86 Japanese GBS patients, electrodiagnostic analysis showed similar frequencies of AIDP (40%) and AMAN (40%). Previous surveys of GBS have not analyzed GBS subtypes, but the incidences of AMSAN and Miller Fisher syndrome (MFS) appear to be lower than those of AIDP and AMAN. Between 1990 and 2005, 205 GBS patients were treated at Chiba University Hospital (Chiba, Japan); of these patients, 69 (33%) were diagnosed as having AIDP, 79 (38%) as having AMAN, and two (1%) as having AMSAN (Kuwabara, Unpublished data). The remaining 55 patients were not classifiable by electrodiagnostic criteria. During the same period, 65 patients with MFS were referred to their institution. 20 The clinical features of diabetes have been recognized over a thousand years ago. However the first description of diabetic neuropathy was by Rollo in 1798 when he 12

13 described pain and paraesthesiae in the legs of a diabetic patient. The primary mechanism initiating nerve damage is hyperglycaemia. There is good evidence that achieving normo glycemia can reduce the frequency of neuropathy. The acute neuropathies generally recover while the chronic neuropathies follow an insidious irreversible course. The neuropathic disorder includes manifestations in both somatic and/or autonomic parts of the nervous system, 23 the classification could be: Mononeuropathies Cranial Proximal motor Isolated peripheral Mononeuritis multiplex Polyneuropathies Sensory / sensory-motor Acute sensory Autonomic Painful neuropathy Radiculopathy (Truncal neuropathy) People with diabetes can, over time, have damage to nerves throughout the body. Neuropathies lead to numbness and sometimes pain and weakness in the hands, arms, feet, and legs. An estimated 50 percent of those with diabetes have some form of neuropathy, but not all with neuropathy have symptoms. The highest rates of neuropathy are among people who have had the disease for at least 25 years. Diabetic neuropathy also appears to be more common in people who have had problems controlling their blood glucose levels, in those with high levels of blood fat and blood pressure, in overweight people, and in people over the age of 40. The most common type is peripheral neuropathy, also called distal symmetric neuropathy, involving both 24,25, 26 lower limbs but which may affect the arms and legs. 13

14 GUILLAIN-BARRÉ SYNDROME (GBS) GBS is the most common cause of acute flaccid paralytic disease in developed countries. During the past 15 years, neurophysiologic, pathologic, and immunologic observations have shown that GBS is divided into the two major subtypes: acute inflammatory demyelinating polyneuropathy (AIDP) and acute motor axonal neuropathy (AMAN). 20 Electrodiagnostic studies play a very important role in diagnosis and classification of subtypes. The pathophysiology and neurophysiology of GBS were not uncovered until one century after the original clinical descriptions of the neuropathy. Thus, other pathophysiologic variants are often considered under the spectrum of GBS, including two axonal forms of GBS: acute motor-sensory axonal neuropathy (AMSAN) and acute motor axonal neuropathy (AMAN), which are pathogenically distinct from the much more common AIDP. Some disorders that appear clinically different from AIDP (e.g., the Miller-Fisher syndrome of ataxia, areflexia, and ophthalmoplegia) may share similar pathogenesis and can be considered a variant of GBS. AIDP is the most common cause of acute generalized weakness. The exact annual incidence of AIDP ranges from 1 4/100,000 population, and there may be a slight male predominance. This neuropathy can occur at any age, with a peak age of onset in the third to fourth decade of life. 27,28 Electro diagnostic testing is a powerful tool 4 for diagnosing and developing treatment plans for patients with diseases of the peripheral nervous system and muscles. It generally includes both a needle electrode examination and a nerve conduction study and can help pinpoint the location of the problem i.e. in the motor neurons, nerve 14

15 roots, peripheral nerves, neuromuscular junction, or muscle and establish the underlying process in these disorders. Each has distinct advantages and limitations, but together they play complementary roles in a comprehensive evaluation of the peripheral nervous system. For this reason, most electro diagnosticians never perform one without the other, except in a few situations in which nerve conduction studies alone are performed earlier than 21 days from the onset of symptoms. Sensory NCSs and F-wave studies have a high sensitivity in PNs and the different techniques complement each other. 29 The distinction between a PN with predominantly axonal loss and a PN with predominant demyelination is one of the major aims of the electrophysiological examination, 29 Jhonsen et al concluded that electro diagnostic studies are valuable in patients with suspected PN and the results may have consequences for prognosis and therapy of individual patients. However large variation in examination techniques, strategies, interpretations and diagnostic criteria have been found among electro myographers thus it is suggested that the value of electro diagnostic studies may be further improved by international standardization. Consistent interpretation of nerve conduction studies, however, is an important step in optimizing diagnosis and treatment of nerve disorders. 4 We in EMG / NCS department commonly see patients of diabetic neuropathy and Guillian Barre syndrome and other poly neuropathies e.g. nutritional, following leprosy, one was pellagra referred for electro diagnosis, it was aimed to identify and study changes of F- responses in the two common conditions Diabetic poly neuropathy (DPN) and GBS. 15