Presentation about late responses f wave h reflex.ppt
- 1. LATE RESPONSES F WAVE AND H REFLEX
- 2. Introduction to late responses Nerve conduction studies are performed to study the distal segment involvement. The late responses are preformed to study the more proximal segment involvement(plexus and roots). We will discuss about two late responses: F wave response H reflex
- 3. Introduction to F-wave Response The name F wave is derived from the first time in the intrinsic muscles of foot by Magladery and McDougal in 1950. The F-wave is a long latency muscle action potential seen after supramaximal stimulation to a nerve. It results from antidromic stimulation of motor neurons involving conduction to and from spinal cord and occurs at the interface between peripheral and central nervous system. The afferent and efferent for F waves are alpha motor neurons. They are produced at the supramaximal stimulus. It is generally accepted that the F-wave is elicited when the stimulus travels antidromically along the motor fibers and reaches the anterior horn cell at a critical time to depolarize it.
- 5. Variability of F-wave Response The F-wave is a variable response and is obtained infrequently after nerve stimulation. So each f- response varies slightly in latency, configuration and amplitude because a different population of anterior horn cells is activated with each stimulation. At least ten trains of F-waves should be obtained and the shortest latency F-wave among them is used.
- 6. F-Response
- 7. Characteristics of F-wave The properties of F waves are as follows: 1. Latency 2. Chronodispersion 3. Amplitude 4. Persistence 5. F-Estimation 6. F wave ratio
- 8. Characteristics of F-Wave Latency: ◦ In the upper extremity, the F response usually occurs at a latency of 25 to 32 ms while in the lower extremity, the F response usually occurs at a latency of 45 to 56 ms. Chronodispersion: ◦ The chronodispersion is basically the maximal F-response latency minus minimal F response latency. ◦ Normal chronodispersion is up to 4 ms in the upper extremities and up to 6 ms in the lower extremities. F responses can be obtained from any motor nerve. Amplitude: ◦ The F response is actually a small CMAP, representing 1% to 5% of the muscle fibers.
- 9. Cont’d Persistency: ◦ Normal F wave persistence usually is 80% to 100% and always above 50%. F-Estimate: ◦ The F estimate takes into account the distal motor latency, the conduction velocity, and the patient‘s limb length to determine whether a prolonged F response is truly due to a lesion of the proximal nerve segment or merely reflects an abnormal distal motor latency or conduction velocity or an unusually tall patient.
- 10. How to elicit F-Response F responses may be absent in sleeping or sedated patients. In these situations, absent or impersistent F responses are not necessarily a sign of pathology. If F responses are not obtained, first ensure that the nerve has been stimulated supramaximally. Second, the Jendrassik (reinforcement) maneuver Can be of help in "priming" the anterior horn cells. The patient can be asked to make a fist with the contralateral hand or clench the teeth prior to each stimulation. This maneuver often will elicit an F response where one was not present at rest.
- 11. Anodal blocking Although F responses typically can be obtained with the stimulator in the standard position (cathode distal), there is the theoretical possibility of anodal block (wherein the nerve hyperpolarizes under the anode, blocking antidromic travel of the action potential from the depolarization site under the cathode).
- 12. MACHINE SETTINGS FOR F-RESPONSE Several adjustments must be made to the EMG machine to record F responses, however. The gain should be increased to 200uV (because the amplitude of the F response is quite low), and the sweep speed should be increased to 5 or 10 ms, depending on the length of the nerve being studied. Supramaximal simulation must always be used, and often it is advisable to turn the stimulator around so that the cathode is more proximal.
- 13. H. REFLEX
- 14. Introduction to H-Reflex The H-reflex is the electrical equivalent of the monosynaptic stretch reflex and is normally obtained in only a few muscles. The H (Hoffmann's) reflex, named after German neurologist Johann Hoffmann who first evoked the response in 1918.
- 16. What is H-Reflex? The H-reflex (or Hoffmann's reflex) is a reflectory reaction of muscles after electrical stimulation of type Ia sensory fibers (Primary Afferent Fibers which constantly monitor how fast a muscle stretch changes) in their innervating nerves. The H-wave, is the expression of a monosynaptic reflex, which runs in afferents from the muscle and back again through efferents of the same muscle.
- 17. H-reflex Definition It is elicited by selectively stimulating the sensory Ia fibres (Primary Afferent Fibers which constantly monitor how fast a muscle stretch changes) of the posterior tibial or median nerve. 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 (large lower motor neurons of the brainstem and spinal cord) motor axon to the muscle.
- 18. H-Reflex
- 19. Location and stimulation The H-Reflex which is monosynaptic reflex consistently obtained in normal adults only, by stimulating the tibial nerve sub-maximally, generally in the popliteal fossa, while recording from either gastrocnemius or soleus muscle, similar to the clinically elicited Achilles reflex. The H.Reflex can also be recorded in median nerve recording from the FCR muscle and stimulating in elbow, and from femoral nerve recording from quadriceps muscles (VM, RF, VL, VI)
- 20. Anatomical location Although the H reflex can be recorded over any portion of the gastrocnemius and soleus muscles, the optimal location that yields the largest H reflex has been studied. If one draws a line from the popliteal fossa posteriorly to the Achilles tendon where the medial malleolus flares out and then divides that line into eight equal parts, the optimal location is at the fifth or sixth segment distally, over the soleus.
- 21. Anatomical localization of H.Reflex
- 22. Application of Electrodes To record the H-Reflex G1 (active recording electrode) is placed 2-3 fingerbreadths distal to the soleus over the two bellies of the gastrocnemius muscle and G2 (Reference Electrode) is placed over the Achilles tendon (usually 14cm distal to G1). Ground electrode is generally placed between G1 and Stimulating electrode (stimulator cathode).
- 23. RECORDING AND STIMULATING SITES
- 24. Normal Values for H.Reflex In normal subjects the latency of H.Wave should be ≤34ms, while recording from tibial nerve, depending on the length of the leg The side to side onset latency difference should be ≤1.5 ms. H/M ratio (maximal H / maximal M amplitude) should be ≤ 50%
- 26. H-Reflex
- 27. CASE 1: F WAVE - SUSPECTED POLYNEUROPATHY History: •Patient: 58-year-old male •Chief Complaint: Gradual onset of numbness and tingling in both feet, ascending to the lower legs over the past 6 months. •Medical History: Diabetes Mellitus Type 2, Hypertension. 27 Neurological Examination: •Bilateral reduction in pinprick and vibration sensation up to the mid-shin. •Mild weakness in toe extension and flexion. •Normal upper limb strength and sensation. •Deep tendon reflexes: Reduced ankle jerks bilaterally. NCS/EMG Studies: •F Wave: • Prolonged latency in lower limb nerves. • Reduced persistence, especially in the tibial nerves. •Nerve Conduction Studies: • Slowed conduction velocities in the sural and tibial nerves. • Reduced amplitudes in sensory and motor responses. Diagnosis: The prolonged F wave latency, reduced persistence, slowed conduction velocities, and reduced amplitudes suggest a generalized neuropathic process. In the context of the patient's history and clinical findings, the diagnosis is consistent with diabetic polyneuropathy. The F wave abnormalities support the involvement of nerve segments distant from usual stimulation sites, indicating a widespread process.
- 28. CASE 2: F WAVE - SUSPECTED RADICULOPATHY History: Patient: 45-year-old female Chief Complaint: Persistent right-sided lower back pain radiating to the right thigh and leg for 3 months. Medical History: No significant past medical or surgical history 28 Neurological Examination: Positive straight leg raise test on the right. Reduced sensation to pinprick in the right L5 dermatome. Weakness in the right big toe extension. Deep tendon reflexes: Reduced right ankle jerk NCS/EMG Studies: F Wave: Prolonged latency in the right tibial nerve compared to the left. Normal F wave latency and persistence in upper limb nerves. Nerve Conduction Studies: Normal conduction velocities and amplitudes in upper limbs and left lower limb. EMG: Signs of acute denervation in the muscles innervated by the right L5 nerve root. Diagnosis: The unilateral prolonged F wave latency in the right tibial nerve, along with clinical signs of radiculopathy (pain distribution, sensory loss, and muscle weakness in the L5 distribution), points towards a right L5 radiculopathy. F wave studies help confirm the proximal involvement, consistent with a root-level lesion.
- 29. CASE 3: H REFLEX - S1 RADICULOPATHY History: Patient: 52-year-old male Chief Complaint: Left-sided low back pain with radiation to the left posterior thigh and calf for 4 months. Medical History: History of lumbar disc herniation 29 Neurological Examination: Positive straight leg raise test on the left. Reduced sensation in the left S1 dermatome. Weakness in the left ankle plantar flexion. Deep tendon reflexes: Absent left ankle jerk. NCS/EMG Studies: H Reflex: Absent H reflex on the left side. Normal H reflex on the right side. Nerve Conduction Studies: Normal sensory and motor studies in the upper limbs. EMG: Chronic denervation in the muscles innervated by the left S1 nerve root. Diagnosis: The absent H reflex on the left, combined with clinical and EMG findings, suggests left S1 radiculopathy. The H reflex is a sensitive indicator of S1 root function, and its absence is consistent with the patient's clinical presentation and history of lumbar disc herniation.
- 30. CASE 4: H REFLEX - MONITORING PROGRESSIVE NEUROLOGICAL DISORDER History: Patient: 60-year-old female Chief Complaint: Progressive weakness in the legs, difficulty in climbing stairs for the past year. Medical History: No significant history. 30 Neurological Examination: Bilateral weakness in lower limbs, more pronounced in proximal muscles. Normal sensation. Deep tendon reflexes: Brisk knee and ankle jerks. NCS/EMG Studies: H Reflex: Reduced H/M ratio bilaterally. Shortened latency of the H reflex. Nerve Conduction Studies: Normal sensory and motor conduction velocities and amplitudes. EMG: Chronic neurogenic changes with signs of active denervation in proximal and distal muscles of the lower limbs. Diagnosis: The reduced H/M ratio and shortened H reflex latency, in conjunction with clinical and EMG findings, suggest a lower motor neuron disorder. These findings, particularly in the context of progressive weakness and EMG evidence of active denervation, may indicate a condition like Spinal Muscular Atrophy or a variant of Motor Neuron Disease. The H reflex helps in monitoring the disease progression and assessing the extent of motor neuron involvement.
- 31. CONCLUSION • The F wave and H reflex are indispensable tools in the neurophysiological evaluation of peripheral nerve disorders. • Their ability to assess nerve segments distant from the stimulation site offers unique insights into the health of motor neurons and proximal nerve structures. • Mastery of the technical nuances and a thorough understanding of the underlying neuroanatomy and physiology are crucial for the accurate interpretation of these tests. • As part of a comprehensive neurodiagnostic evaluation, they provide invaluable information guiding the diagnosis, management, and prognostication of various neuropathic conditions. 31
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