Hi physio students, its all take from 'claytons electrotherapy' book.

1. ELECTOROMYOGRAPHY
Prof. Dr. M. Rajesh, PT, M.P.T(cardio), BCRC
TRINITY MISSION AND MEDICAL
FOUNDATION
MADURAI

2. INTRODUCTION
 Electromyography is recording electrical activity of muscle
through the coaxial needle electrode. diagnostic
electromyography is examine first with the muscle at rest then
doing voluntary activity. Motor units consist anterior horn cell
and its divisions arising from that's lt and the muscle fibres are
supplied by these divisions. The number of muscle fibres in
motor units where is from 30 in external ocular muscles and in
2500 large muscles. The fewver the fibres in units the more
precise the voluntary control.

3. SPONTANEOUS ACTIVITY
 Normal muscles is electrically silence during at rest. This
discharges are initially in the deflection and of higher frequency
then fibrillation potentials. Small negative deflections due to end
plate potentials main also be seen occasionally.

4. ABNORMAL SPONTANEOUS
ACTIVITY
 It can only be properly observe when the needle is at rest,
because activity due to irritation by the needle occurs briefly
after the needle is inserted into normal muscle. Abnormal
spontaneous activity may be classified into
 fibrillation potentials
 positive shark waves
 fasciculation potentials and
 high frequency discharges.

5. FIBRILATION POTENTIALS
 Bi or triphasic of 1 to 2 ms duration and 50 to 300 microvolts
amplitude. They are due to spontaneous excitation of individual
muscle fibres and appear 10 to 20 days after nerve
degeneration.

6. POSITIVE SHARP WAVES
 It gives a sharp initial positive deflection followed by a
prolonged negative phase. Amplitude differentiates widely
between 50 and 2000 microvolts.

7. FASCICULATION POTENTIALS
 Spontaneous discharges from motor units not under voluntary
control. They consist of potentials repeating at lower rates then
fibrillation. Fasciculation potentials maybe three phases and
maybe highly complex and although maintain owe
characteristics appearance on screen, it is differ widely in size
and shape from one to another. The amplitude is 0.5 to 3 mv
and 7 to 20 ms durations being characteristics of muscle twitch
visible to naked eye. It is clearly seen in motor neuron diseases
when fibrillation and positive potentials also occur.

8. HIGH-FREQUENCY DISCHARGES
 It is occur in myotonia especially dystrophia myotonica and
occasionally with polymyositis. They gives characteristics of
“dive Boomer” sound of the loudspeaker.

9. VOLITIONAL ACTIVITY
 Recordings are made first on minimal volition and then with
increasing strength of muscle contraction. Potentials recorded
from normal individual motor units differ in amplitude and
duration depending on the number of muscle fibres composing
of motor units. The motor unit itself consist of muscle fibres the
nerve fibres supplying them and the parents anterior horn cell.
The motor units in the phase are much smaller then those in
the Limb muscles and as a consequence the potentials recorded
from them are shorter in duration and smaller in amplitude.

10.  Normal motor units potentials have 3 or 4 phase and at first
repeats 10 to 15 times per second. Other units then firing to
give the confused pattern of electrical activity displayed on the
screen.

11. DENERVATION
 Denervation causes reduction in the number of motor units
acting with the consequent reduction in the interference
pattern. In cases of severe the denervation parts of the baseline
are visible even at maximum volition so called ‘discrete’
Interference pattern. With complete denervation no motor units
are electrically active.

12. REINNERVATION
 Reinnervation after the injury causes nascent polyphasic units to
appears. At first of only few hundred microvolts amplitude.

13. PERIPHERAL NEUROPATHY
 Peripheral neuropathy makes earliest interference pattern of
motor units with the increased polyphasic units on vollition as
well as abnormal spontaneous potentials. Similar changes occur
in presence of the anterior horn cell as motor neuron diseases.
But the polyphasic potentials are usually much larger up to 3 or
4 microvolts have amplitude. They are easily seen in the
anterior tibial and small hand muscles. Now conduction studies
combined with the AMG findings make it possible to distinguish
between peripheral neuropathy and other Pathology in the
spinal cord.

14. MYOPATHY
 Myopathy causes a loss of individual motor fibres. There is no
reduction in the total number of motor units at first, but a
reduction of the interference pattern occurs later in the disease.
The motor units discharges appears smaller and short then is
normal for the muscle under examination with increase number
of polyphasic units. these changes are substantially the same
whatever the causes of myopathy e.g carcinoma, thyrotoxicosis,
Muscular dystrophy and steroid treatments. A few high
frequency discharges may be heard and seen in Many
myopathies, but are mostly seen with myotonia.

15. MYOSITIS
 In which the muscle is inflamed causes changes in the volitional
pattern. Fibrillation potentials are also occur in about 50 % of
cases.

16. THANK YOU
Prof. Dr. M. RAJESH, PT,M.P.T(cardio),B.C.R.C
TRINITY MISSIOIN AND MEDICAL
FOUNDATION
MADURAI.
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