H - Reflex in Lumbosacral Radiculopathy

Original Editor - Gayatri Jadav Upadhyay

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Introduction

Radiculopathy is not a specific condition, but rather a description of a problem in which one or more spinal nerves are affected. The nerve or nerves may be inflamed, had lack of blood flow, or may be affected by a disease in part or totally. Lumbosacral radiculopathy (LSR) is a common clinical problem that involves L5and S1 nerve roots.

Prevalence

It may affect anyone at any time in their lives, regardless of their sex, age and profession. About 80-90% of adult population suffers from backache during their life. LSR comprises 62% to 90% of all radiculopathies. It was reported to be 9.8 per 1,000 populations in Sicily, Italy. It was found to be higher in factory workers, housewives, and clerks. Majority of the cases are benign. Each year 3-4% of the population is temporarily disabled and 1% of the working age population is totally disabled from low back ache. 90% recover spontaneously in 4-6 weeks.

Lumbosacral radiculopathy occurs in approximately 3-5% of the population, and men and women are affected equally, although men are most commonly affected in their 40s, whereas women are most commonly affected between ages 50-60. Of those who have this condition, 10-25% develops symptoms that persist for more than 6 weeks. Ninety eight percent of low backache is due to prolonged sitting because of production of highest vertical load on the spine at L4-L5 and L5-S1 level.

Causes

Langston, Garant (1985) showed that the herniations of the intervertebral disc are the commonest cause of radiculopathy. The majority of them occur at lower three disc levels approximately: 43% at L5-S1, 47% at L4-L5, 3% at L2-L3 or L1-L2. There is tendency of Backache to recur.
Generally, LSR occurs as a result of disc herniation or acute injury in younger population and as a result of foraminal narrowing from osteophyte formation in older population. It may also result from spinal cord injuries, spinal stenosis, spinal diseases and other conditions. LSR often results in persistent disability, so extensive medical evaluation and aggressive treatment is essential^.
LSR results from either degenerative changes or intervertebral disc herniation. Degenerative changes in the spine including lumbosacral region are being found virtually in the older people. These changes may consist of bone enlargement and osteophyte encroachment either into the spinal canal, causing central stenosis, or into the vertebral foramen, leading to foraminal stenosis. Both central and foraminal stenosis are most likely to cause various degrees of LSR.

Furthermore, degenerative changes in the spine are associated with the obstruction of the epidural veins and fibrosis in and around the nerve roots .Venous obstruction may lead to perineural anoxia and the development of perineural fibrosis and neural atrophy. Distended veins in the epidural plexus, damaged pain receptors in the nerve root sheaths, and loss of neurons could lead to chronic radicular symptoms.

Symptoms

Back pain is one of the ten most common neurological problems seen by family practitioners. Lumbosacral radiculopathies produce the syndrome of sciatica; the root pain of sciatica is almost invariably accompanied or preceded by back pain (94%). The intervertebral disc lying between vertebrae L4 and L5 is called the L4/5 disc. The disc between the L5 vertebrae and the sacrum is the L5/S1 disc. Since the L4 root emerges above the L4/5 disc, a lateral herniation of the L4/5 disc damages the L5 root. Moreover, a lateral herniation of the L5/S1 disc damages the S1 root.

Disc herniations in lumbosacral region were classified as central, paracentral, intraforaminal, extraforaminal and multiregional broad-based protrusions. Anatomical position and form of the disc herniation are of prognostic value for the clinical outcome. Pressure on the lumbosacral nerve root associated with herniated disc or contusion of the sciatic nerve can result in pain radiating down the lower extremity to the foot. The onset of symptoms in patients with lumbosacral radiculopathy is often sudden and includes LBP. Some patients state the preexisting back pain disappears when the leg pain begins. Sitting, coughing, or sneezing may exacerbate the pain, which travels from the buttock down to the posterior or posterolateral leg to the ankle or foot. This pain is sharp and severe, traveling quickly down the back of the leg, sometimes to the ankle or foot. Muscle weakness or spasm may also be present, either during the attack of pain or afterwards. Numbness or tingling may be felt in the leg, ankle or foot, depending on which nerve root is involved.

Diagnosis

In the field of physiotherapy there is a growing interest towards developing an evidence based practice of diagnostic procedures used in the physiotherapy. Low back pain and LSR constitute a major part of daily load for physiotherapists worldwide, and have been evaluated with various methods. As this is subjective, a need for a more objective method for evaluating the efficacy of the diagnostic procedure was required. Among these methods is Electrodiagnosis. Neurophysiologic testing and H-reflex in particular provides an objective assessment of nerve root compression or entrapment. It has been found to be a clinically useful method in the diagnosis of radiculopathies. It is also reported to be an objective tool in measuring the degree of compression and decompression on the compromised nerve root in patients with radiculopathy.
Spinal imaging procedures including radiography, CT, MRI, myelography, objectively provide detailed visualization of spinal anatomy, but are unable to determine which findings are the sources of pain. Poor correlations were reported between back pain and degenerative changes seen in radiographs and magnetic resonance imaging scans. Many changes seen on the radiographs of symptomatic patients are also seen in the radiographs of asymptomatic patients. Radiographs are generally not recommended during the first month of the patient’s symptoms if there are no red flags. MRI has demonstrated excellent sensitivity in the diagnosis of lumbar disc herniation and is considered the imaging study of choice for nerve root impingement. However, this preference is tempered by the prevalence of abnormal findings in asymptomatic subjects.

MRIs are not necessary in all patients who have examination findings that are consistent with a radiculopathy; in fact, these studies should generally be reserved for those cases in which the imaging results are likely to guide treatment. When physical examination and electrodiagnostic findings do not indicate the exact levels of pathology in a patient who is in need of a selective nerve root block, MRI may help the physician to determine the exact level of pathology.

Management / Interventions

LSR is most likely to present with pain and other sensory symptoms more than motor symptoms³. It has been reported to cause functional disability, emotional stress and sleep disturbance²⁵. It can be managed surgically or all ages, with high management cost non-surgically. The surgical management mainly includes discectomies and laminectomies. The non-surgical management includes medications, rest and physiotherapy. It has been estimated that 10 to 50 % of patients with LBP receive physiotherapy^25-29. Recovery from LSR is less frequent than localized lower back pain³⁰. Clinically, physiotherapy treatment for back pain and radiculopathy is provided in the form of cold, heat, electromagnetic waves, ultrasound, mobilization, manipulation, massage, corset use, traction, electrical stimulation, acupuncture, Maitland technique, Cyriax technique, McKenzie method and home instruction.

Electrophysiological studies in Radiculopathy

In the era of modern neuroimaging methods, the electrophysiological examination remains an essential diagnostic tool. It is a critical way station in the clinical decision making process, dictating whether imaging studies or other tests are required. In addition, the electrophysiological examination enables the clinician to decide what regions should be imaged.³⁶

The electrophysiological evaluation of root or spinal cord disease is complementary to neuroimaging studies, providing information about functional rather than anatomical integrity and information that is important for diagnostic and prognostic purposes.³⁷

Electrodiagnosis attempts to answer where in the neuraxis there is pathology: anterior horn cells, spinal cord nerve roots, proximal or peripheral nerve trunks, terminal axons or sensory fibers, end plate or the myocytes. It may answer the distribution anatomically: one or more nerves, symmetrical or asymmetric. Decisions can be made about the nature of the pathophysiology – myelin or axonal. It can inform us regarding the age or chronicity of the pathology and sometimes assist in prognostication. It can allow one to be more focused in ordering more expensive diagnostic tests such as MRI or more invasive procedures such as muscle or nerve biopsy.^38-43

The electrophysiological findings help to localize a lesion but are not pathognomonic of specific diseases.³⁷ The findings may also provide insight into underlying physiological mechanisms that have been disrupted.³⁷ The electrodiagnostic evaluation assesses the integrity of the lower-motor-neuron unit (i.e., peripheral nerves, neuromuscular junction, and muscle).⁴⁴ The electrodiagnostic examination is a useful tool for first detecting abnormalities and then distinguishing problems that affect the peripheral nervous system.⁴⁴ Electrodiagnostic studies should be considered an extension of the history and physical examination and not merely a substitute for detailed neurologic and musculoskeletal examinations.⁴⁵ Additionally, these studies can provide useful prognostic information by quantifying the extent and acuity of axonal involvement in radiculopathies. ⁴⁵

Performing late response tests, such as the H-reflex, can provide valuable information regarding the proximal nerve/nerve root involvement.⁴⁵ The H-reflex is both a sensitive and specific marker for involvement of the S1 root and will be prolonged from the time of symptom onset.³⁴
Furthermore, these studies do not assess the smaller myelinated and unmyelinated nerve fibers, which are typically responsible for pain transmission.⁴⁵ If the patient has had previous episodes of radicular symptoms or previous spinal surgery, it may be useful both from a diagnostic perspective and from a medicolegal standpoint to perform initial electrodiagnostic studies as soon as possible after the appearance of new symptoms in order to differentiate later developments from preexisting disease.³⁴

Electrodiagnostic testing is not a substitute for a thorough neurologic examination, which should focus on muscle power, reflexes, and sensation.⁴⁶
- Failure to wean from a ventilator, traumatic nerve injury, leg weakness with sensory loss and diminished reflexes, and postoperative weakness are among the indications for electrodiagnostic testing.⁴⁶
- Relative contraindications to electrodiagnostic testing include external pacemakers and defibrillators, severe coagulopathy, and testing a limb with a central line.⁴⁶

Specific electrodiagnostic studies used for radiculopathy are as follows:⁴⁷
Nerve conduction studies: Distal peripheral motor and sensory nerve conduction studies are often normal in a single-level radiculopathy. They are useful for assessing possible axon loss and/or demyelination. Nerve conduction studies may rarely be abnormal in radiculopathies but are needed to be certain other conditions that may produce similar symptoms and signs are not present. H reflexes and F waves probably have roles in the evaluation of radiculopathies but published reports about F waves in radiculopathies have been marred by inadequate methodology.

Needle electromyography: This measures electrical activity directly from muscle and provides information about the integrity of the motor unit; it can be used to detect loss of axons (denervation) as well as reinnervation. This technique offers a high diagnostic yield. Timing is important, and the study should be performed less than 4-6 months (but >18-21 d) from symptom onset. Needle electromyography is the best established of these procedures but has the disadvantage of requiring injury to motor fibers of both a certain degree and distribution.
Radiculopathy workup – In Acute Radiculopathy >3 days <3 weeks, H-Reflex (NCS version of ankle jerk) can be helpful in diagnosing a S1 radiculopathy, when compared side-to-side. Otherwise, denervation/injury potentials are best seen on needle EMG after 2-3 weeks after initial injury. Therefore, EMG is best ordered for radiculopathy around 2-3 weeks after. However, keep in mind that needle EMG only picks up “bad” radiculopathies, i.e. with axonal loss. For this reason, EMG may not pick up isolated small fiber neuropathic processes, i.e. C Fiber, pain fibers. NCS are generally not as useful in diagnosing radiculopathies, since the lesion pre-ganglionic.⁴⁸

Somatosensory evoked potential studies (SSEPs): These studies are essentially of no value in the assessment of acute LBP and radiculopathy. SSEPs are not indicated unless the patient’s neurologic signs and symptoms are suggestive of pathology that would indicate involvement of the somatosensory pathways.⁴⁵

H-Reflex in Lumbosacral Radiculopathy

Late potentials are electro diagnostically elicited responses in muscle that appear more than 10-20 milliseconds after stimulation of motor nerves. They have been termed “late potentials” because they take substantially longer to appear than the direct responses to stimulation of motor nerves. There are two distinct types of late responses, the H-Reflex and the F-response.⁴⁹

Traditional nerve stimulation techniques used in an electrophysiology laboratory primarily assess the distal segments of the peripheral nerves. Methods of testing the proximal nerve segments or the central nervous system include, blink reflex, F wave, the H reflex, T reflex, tonic vibration reflex, and the silent period. The reflex studies reveal conduction characteristics along the entire course of the sensory and motor axons as well as the excitability of the neuronal pool.⁵⁰

Extensive studies have proven the practical value of the H reflex in certain neurologic disorders. Neurologic examination exploits the muscle stretch reflex to measure motor neuron excitability in many conditions. Clinical observation, however, falls short in objectively evaluating the briskness, velocity, or symmetry of these responses. Electrophysiologic recordings offer these advantages by quantifying the response after an electrical stimulation of the tibial nerve.⁵⁰

The first type of “late response” was described by Hoffmann in 1918 hence it is named as H-Reflex.⁵¹ The pathway for this reflex and the significance of abnormalities is easiest to understand by recognizing that it is basically the electrophysiologic equivalent of the muscle stretch reflex. The H-reflex is a monosynaptic reflex elicited by sub maximal stimulation of the tibial nerve and recorded from the calf muscle.^52-53

The H-Reflex is an electrical analogue of the monosynaptic stretch reflex elicited by bypassing the muscle spindle and is normally obtained in only a few muscles.⁵⁵ It is elicited by selectively stimulating the Ia fibers of the posterior tibial or median nerve.⁵⁴ Such stimulation can be accomplished by using slow (less than 1 pulse/second), long-duration (0.5-1 ms) stimuli with gradually increasing stimulation strength.⁵⁴

The stimulus travels along the Ia fibers, through the dorsal root ganglion, and is transmitted across the central synapse to the anterior horn cell which fires it down along the alpha motor axon to the muscle.⁵⁶ The result is a motor response, usually between 0.5 and 5 mV in amplitude, occurring at low stimulation strength, either before any direct motor response (M) is seen or with a small M preceding it.⁵⁶ Understandably, the latency of this reflex is much longer than that of the M response and a sweep of 5-10 ms/division is necessary to see it.⁵⁶

The H-reflex can normally be seen in many muscles but is easily obtained in the soleus muscle (with posterior tibial nerve stimulation at the popliteal fossa), the flexor carpi radialis muscle (with median nerve stimulation at the elbow), and the quadriceps (with femoral nerve stimulation).⁵⁷ Typically, it is first seen at low stimulation strength without any motor response preceding it. As the stimulation strength is increased, the direct motor response appears. With further increases in stimulation strengths, the M response becomes larger and the H-reflex decreases in amplitude. When the motor response becomes maximal, the H-reflex disappears and is replaced by a small late motor response, the F-wave.⁵⁶

Neurophysiological testing, in particular H-reflex described by Hoffman⁵⁸, has been used recently to assess the neurophysiological changes in the compromised nerve root and to evaluate the efficacy of some of non-surgical managements on patients with radiculopathy.¹⁵
H-reflex has two parameters, amplitude and latency. The amplitude is used to monitor spinal activity whereas, latency usually assess the sensory and motor conductivity. H-reflex latency can be determined easily from charts, according to height and sex or from published normal values.¹⁵ Whatever these values however, the best normal value in localized processes is the patient’s asymptomatic limb.⁴⁵ If no facilitation maneuvers are performed, the difference in latency between both sides should not exceed l ms.⁴⁵ Latency is related to height, but not age or obesity⁵⁸.

The H-reflex is useful in the diagnosis of S1 and C7 root lesions as well as the study of proximal nerve segments in either peripheral or proximal neuropathies.⁴⁵

Its absence or abnormal latency on one side strongly indicates disease if a local process is suspected.⁴⁵ Much controversy remains, however, on whether its absence bilaterally in otherwise asymptomatic individuals is of any clinical significance.⁴⁵
Using routine electrodiagnostic procedures, the authors searched for physiologic evidence of nerve root compromise. The soleus H-reflex appeared to be a sensitive indicator of sensory fiber compromise at the S1 root level, because changes correlated well with the focal sensory signs and preceded clinical and electromyographic signs of motor root involvement.⁵⁹ When these occurred, the clinical findings were consistent with a more severe nerve root deficit and with radiographic evidence of neural compression. The greater sensitivity of the soleus H-reflex may be related to the pathophysiologic events that occur at the lesion site.⁵⁹

With the notable exception of the triceps surae muscle, the H reflex is very difficult to elicit. This limits the H-reflex to being a sensitive specific and quantitative test of sciatic nerve and S1 nerve root function.⁴⁹ This may be of utility in investigating patients with suspected S1 radiculopathy.⁶⁰

“H-reflexes” measured in muscles below the knee other than the soleus may represent volume conducted signals. The authors recognize that true H reflexes are potentially measurable in the anterior tibialis and peroneus longus muscles, though they were unable to observe them. A preliminary validation of signal origin in all research protocols utilizing non-soleus H-reflexes is recommended. Further, the clinical application of peroneus longus and anterior tibialis H-reflexes to assist in isolation of lumbar radiculopathy is discouraged.⁶¹

In cases of an absent H reflex in the relaxed muscle, the latency of an H reflex recorded by facilitation could be compared equally with that of the recording in relaxation.⁶² Studying the H-reflex instead of the stretch reflex has both limitations and advantages. One limitation is that it does not reflect changes in fusimotor activation or musculotendon mechanics during movement because it bypasses the muscle spindle. As a result, it is possible that H-reflex modulation is not always behaviorally relevant. However, circumventing changes in fusimotor activation and musculotendon mechanics can be advantageous because it allows for an examination of spinally mediated reflex modulation.⁶³
H reflex has been used to assess the effects of therapeutic interventions such as spinal manipulation, massage, sacro-iliac joint manipulation, cervical traction, tendon pressure and transcutaneous electrical nerve stimulation.⁶⁴

Spondylotic and spondylolisthetic changes commonly occur at L5-S1 vertebral level which gives rise to radiating pain and weakness along the course of the nerve.⁶⁵ This causes decrease in the Achilles tendon jerk which can be ultimately clinically correlated by the help of H-Reflex studies. Weintraub J. R., Madalin K., Wong M. investigated that there is a high correlation between Achilles tendon jerk and Soleus H-Reflex.⁶⁶ These changes causes back pain in adults.

Mazzocchio R. et al (2001) proved that the recruitment curve of the soleus H-Reflex is the more appropriate test for detecting sub clinical nerve root dysfunction at L5-S1 level.⁶⁸ F.Ginanneschi et al (2006) proved that the changes in H-Reflex excitability may underlie a decrease in the gain of a peripheral sensor in Chronic Low Back Pain.⁶⁹ Bologinini A. Palma L (1999) suggested that the Soleus H-Reflex recruitment curve is a possible early indicator of S1 root dysfunction.⁵⁹

The H-reflex has also been used to determine the position causing maximum spinal root decompression in cervical and lumbosacral radiculopathies and to determine the effect of prone position ⁷¹ and IFT in patients with LSR as well as to determine the effects of traction and retraction on compressed spinal root in patients with cervical radiculopathy. ^70,72

Abnormal soleus H-reflex showed good correlation with S1 sensory impairment and equally useful in acute or chronic S1 radiculopathy^15. Prolonged onset latency, absence of or both of H-reflex on the affected side are the most commonly used measures of the H-reflex⁷³. H-reflex latency is considered abnormal in case of a side to side difference of more than 2 msec, while a two- to four- fold side-to-side difference can be seen in H-reflex amplitude.⁷⁶

G. Medina et al retrospective studies supported the established concept that the H-reflex study is a useful tool in the evaluation of S1 radiculopathy. The H-reflex showed a better correlation, than the ankle muscle stretch reflex, with positive electromyographic findings of S1 radiculopathy.⁷⁴

The most frequent category used for diagnosis of lumbosacral radiculopathy was abnormal needle EMG; this occurred in 65.66% of the cases. Abnormal EMG and abnormal H-waves were seen in 13.84% of the cases and isolated abnormal H-waves were seen in 4.85% of the cases. Abnormalities seen on both needle EMG & F-wave testing in a study or abnormal F-waves as the sole abnormality on the test were seen in only 3.43% and 0.62% of cases respectively.⁷⁷

Han T.R. et al (1997) validated from all H parameters studies that a new diagnostic criterion of abnormal response as follows:
(1) H latency difference over 1.0 msec and H/H amplitude ratio less than 0.5 or
(2) H latency over 30 msec or
(3) Unilateral absent evoked H response.⁷⁸

The high false-positive rate of magnetic resonance imaging (MRI) makes it a less-than-reliable tool for evaluating clinically significant stenosis. Finding MRI changes that correlate with electrodiagnostic abnormalities might lead to more successful treatment decision making. MRI measurements did not differ significantly with respect to extremity needle electromyography findings in the entire population or in patients with clinical signs of lumbar stenosis. In the entire population, an absent tibial H-wave corresponded to the interfacet ligament distance at L5-S1 and anterior to posterior canal size at L4-5.⁷⁹

Recent Related Research (from Pubmed)

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2: Sinanovic O, Custovic N. Musculus extensor digitorum brevis is clinical and electrophysiological marker for L5/S1 radicular lesions. Med Arh.
2010;64(4):223-4. PubMed PMID: 21246920.

3: Sandoval AE. Electrodiagnostics for low back pain. Phys Med Rehabil Clin N Am. 2010 Nov;21(4):767-76. doi: 10.1016/j.pmr.2010.06.007. Review. PubMed PMID: 20977959.

4: Emad MR, Gheisi AR. A complementary approach for evaluating S1-root in diabetic neuropathic patients. Electromyogr Clin Neurophysiol. 2010
Jan-Feb;50(1):61-4. PubMed PMID: 20349560.

5: Tataroglu C, Deneri E, Ozkul A, Sair A, Yaycioglu S. Adductor T reflex abnormalities in patients with decreased patellar reflexes. Muscle Nerve. 2009 Aug;40(2):264-70. doi: 10.1002/mus.21299. PubMed PMID: 19609916.

6: Beyaz EA, Akyüz G, Us O. The role of somatosensory evoked potentials in the diagnosis of lumbosacral radiculopathies. Electromyogr Clin Neurophysiol. 2009 May-Jun;49(4):131-42. PubMed PMID: 19534290.

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