ABNORMAL AND NORMAL SPONTANEOUS ACTIVITY
- 1. SPONTANEOUS ACTIVITIES: NORMAL AND ABNORMAL BY: SAMIULLAH ZAFAR Neurodiagnostic technologist Ziauddin University Karachi.
- 2. SPONTANEOUS ACTIVITY A normal muscle at rest exhibits electrical silence, any activity seen during the relaxed state can be considered abnormal Such activity is termed as spontaneous because it is not produced by voluntary muscle contraction. All SA is abnormal, with the exception of potentials that occur in the muscle end plate zone(i.e, NMJ) Two types of SA occur here: 1. End plate noise 2. End plate spikes
- 3. SPONTANEOUS ACTIVITY: NORMAL 1.Endplate Noise: These are Low-amplitude Monophasic negative potentials Fire irregularly at 20-40 Hz “seashell” sound on EMG Physiologically, they represent MEPPs Recognized by characteristic shape and sound and by frequent association with endplate spikes
- 5. 2.Endplate spikes (Nerve Potentials) Are MFAPs that fire irregularly upto frequency of 50 Hz Seen along with endplate noise Biphasic, with an initial negative deflection Cracking, buzzing, sputtering sound on EMG Key features that differentiate endplate spikes from fibrillation potentials are 1.initial negative deflection 2.highly irregular firing rate
- 7. SPONTANEOUS ACTIVITY: ABNORMAL MUSCLE FIBER POTENTIALS 1.Fibrillation potentials: These potential derived from extracellular recording of single muscle fiber Recognized by their single MFAP morphology: A brief spike with an initial positive deflection 1-5 ms in duration Low in amplitude (10-100uv) Firing pattern is very regular with a rate usually 0.5-10 Hz, occasionally upto 30 Hz. On EMG sound like “rain on the roof”. Are electro physiologic markers of active denervation.
- 9. 2. Positive sharp waves: (PSW) Have same significance as fibrillation potentials: Are spontaneous depolarization of a muscle fiber and signify active denervation. Have brief initial positivity followed by a long negative phase. On EMG sound like “dull pop”. Amplitude is variable(10-100uv, up to 3mV) Regular firing pattern, with a rate usually between 0.5 and 10 Hz
- 11. GRADING When positive sharp waves and fibrillation potentials are present in a muscle, they are graded on a scale from 0 to 4 as follow 0 None present +1 Persistent single trains of potentials (>2-3 sec) in atleast 2 areas +2 Moderate number of potentials in three or more areas +3 Many potentials in all areas +4 Full interference pattern of potentials
- 12. 3.Complex repetitive discharges: are action potentials of a group of muscle fibers that discharge spontaneously in near synchrony in a regular, repetitive fashion. They are originated by the spontaneous depolarization of a single fiber, followed by ephaptic spread to an adjacent muscle fiber. High-frequency(5-100 Hz) Amplitude 50-500 microvolts Duration upto 50 ms Abrupt onset and termination Create “machine-like” sound on EMG Occur in both chronic neuropathic and myopathic disorders
- 14. 4.Myotonic Discharges: Is spontaneous discharge of a muscle fibre (similar to fibrillation and PSW) but is differentiated by its characteristic waxing and waning of both amplitude and frequency Firing rate is between 20-150 Hz Myotonic potentials have either a positive wave or brief spike morphology Characteristic “revving engine” sound on EMG seen in myotonic dystrophy, myotonia congenita, and paramyotonia congenita
- 16. SPONTANEOUS ACTIVITY: ABNORMAL MOTOR UNIT POTENTIALS 5. Fasciculation Potentials: Is a single, spontaneous involuntary discharge of an individual motor unit Fire very slowly and irregularly, less than 1-2 Hz They can have the morphology of simple motor unit action potentials (MUAPs)or they can be complex and large if they represent a pathologic motor unit. Have sound of “ corn popping” on EMG common in chronic neurogenic diseases such as radiculopathies, axonal peripheral neuropathies, and anterior horn cell disorders (ALS, SMA).
- 18. 6. Myokymic Discharges: Myokymic discharges are groups of recurring spontaneous firing MUAPs that fire in a repetitive burst pattern. The discharge is brief, repetitive firing of single MUAPs for a short period (up to a few seconds) at a rate of 40 to 60 Hz. This is followed by a short period (0.1 to 10 seconds) of silence, with the repetition of the same sequence for a particular potential. They have a regular or semi-rhythmic pattern and a sound like “marching soldiers.” Most commonly, these are found with radiation-induced nerve injury, chronic compressive neuropathies, or poly radiculopathies.
- 20. 7.Neuromyotonic Discharges: High frequency (150-250 Hz), decrementing, repetitive discharges of single motor unit Characteristic “pinging” sound on EMG They start and stop abruptly These are seen in disorders of peripheral nerve hyperexcitability (Isaac and Morvan syndromes). It may occur as a result of a defect in the potassium channel in the nerve membrane.
- 22. THANKS