1. Dr. Emmanuel Fournier La Salpêtrière Hospital, Paris, France
EMG protocol for periodic paralyses and myotonic syndromes diagnosis Long and repeated short exercise tests
Dr. Emmanuel Fournier
La Salpêtrière Hospital, Paris, France

2. Overview of the protocol
The EMG protocol includes several tests performed successively or simultaneously in order to reduce the total examination duration :
Long (5 mn) exercise test on right hand, with post-exercise rest
Repeated short (10s, three times) exercise test performed two times, on left hand and on right foot
Needle electromyography of five muscles
References for the precise description of technical conditions, protocol and main results :
Fournier, E.M.Inter, Cachan, 1998, pp
Fournier et al. Annals of Neurology, 2004, 56:
Fournier, Rev Neurol (Paris), 2005, in press

3. Preparation Three sets of surface recording electrodes are installed
Best stimulation and recording sites are located
Baseline compound muscle action potentials (CMAP) are recorded
Recording electrodes are left in the optimal position throughout the examination
The purposes are threefold :
Electrodes will serve to different exercise tests
A rapid nerve conduction study checks the absence of nerve alterations. If necessary, neuromuscular transmission is tested by 3 Hz repetitive nerve stimulation.
Baseline recordings would serve as reference values if an attack of paralysis occurs during the examination

4. Preparation (I, II, III)
Recording of the extensor digitorum brevis (EDB) muscle
Stimulation of the anterior tibial nerve
Electrodes will be used for one of the repeated short exercise tests
Recording of the left abductor digiti minimi (ADM)
Stimulation of the ulnar nerve
Recording of the right abductor digiti minimi (ADM)
Electrodes will be used for the long exercise test

5. Preparation (IV)
A bandage prevents articulation displacements and changes in muscle volume during the exercise tests
Skin temperature is measured and must be maintained between 32 and 34°C throughout the EMG session
The purpose is to prevent any decrease in CMAP amplitude and area which could be caused by muscle warming during the examination

6. Long exercise test on right hand (I)
CMAP is monitored before exercise (top trace)
The subject is asked to spread the little finger as strong as possible against resistance during 5 minutes
Brief resting periods (2-3 seconds) are respected every seconds to prevent ischemia
After completion of the exercise, the subject is instructed to completely relax while CMAP are recorded
2 seconds immediately after cessation of exercise (second trace)
and then 30 seconds after (third trace)

7. Long exercise test (I) Normal changes immediately after exercise
Immediately after exercise cessation, normal results are :
Slightly decreased amplitude (-6 %) of the CMAP
Increased duration (+38 %) disappearing in 30 seconds
If the amplitude decline is more marked, it must be carefully checked that nerve stimulation is still supramaximal

8. Long exercise test (I) Immediate changes after exercise cessation in muscle channelopathies
Patients with Paramyotonia Congenita
Decreased CMAP amplitude
Presence of Post-exercise myotonic potentials (PEMP)
Patients with Periodic Paralysis
No change of the CMAP in most cases
Early decreased amplitude if an attack of paralysis has been triggered by the exercise achievement
Increased amplitude in patients with Hyperkalemic Periodic Paralysis, especially when pre-exercise CMAP amplitude was small

9. Long exercise test (II) Changes 1-5 minutes after exercise
CMAP is recorded every minute during the first 5 minutes after exercise cessation (traces 4-8 on the screen)
Normal results during this rest period are no change of the CMAP as compared with pre-exercise values :
Otherwise, it must be carefully checked that nerve stimulation is still supramaximal

10. Long exercise test (II) Changes 1-5 minutes after exercise in muscle channelopathies
Patients with Paramyotonia Congenita
Disappearance of PEMP, persistence of decreased CMAP amplitude
Patients with Periodic Paralysis
No change or progressive decline of CMAP amplitude
Persistence of the increased amplitude if previously present, in Hyperkalemic Periodic Paralysis

11. Continuation of the long exercise test
CMAP of the right ADM is recorded every 5 minutes during the 40 minutes rest after exercise cessation.
Recording electrodes and bandage are left on the right hand
During the 5 minutes interval between two recordings, different others tests are performed :
Repeated short exercise test on the left hand
Repeated short exercise test on the right foot
Search for myotonic discharges by needle-EMG

12. Repeated short exercise test on left hand (I)
A second bandage is installed on the left hand, and CMAP of the ADM is monitored before exercise (top trace)
The subject is asked to spread the little finger as strong as possible against resistance during 10 seconds
After completion of the exercise, the subject is instructed to completely relax while CMAP are recorded at rest :
2 seconds immediately after cessation of exercise (second trace)
and then every 7-8 seconds for 50 seconds (traces 3-8 on the screen)
This sequence (10 s contraction - 50 s rest) is repeated three times

13. Repeated short exercise test (II) Normal CMAP changes after exercise
Immediately after exercise cessation, normal results are :
Slightly increased amplitude (+5 %) of the CMAP (second trace)
Return to pre-exercise values in 10 seconds (third and next traces)
If an amplitude decline appeared, it must be carefully checked that nerve stimulation is still supramaximal

14. Repeated short exercise test (II) CMAP changes between the exercises in muscle channelopathies
Patients with myotonic syndromes
Presence of Post-exercise myotonic potentials (PEMP) immediately after the first short exercise, especially in Paramyotonia Congenita
Decrease in CMAP amplitude, worsening or disappearing with repeating exercise in Paramyotonia Congenita and Myotonia Congenita respectively
Patients with Periodic Paralysis
No change of the CMAP in most cases
Increased amplitude in patients with Hyperkalemic Periodic Paralysis, worsening with repeating exercise, especially when pre-exercise CMAP amplitude was small

15. Long exercise test (III)
Back to the right hand for recording CMAP of the ADM at 10 minutes rest after exercise cessation.
If an amplitude decline appeared, it must be carefully checked that nerve stimulation is still supramaximal

16. Repeated short exercise test on right foot
CMAP of the EDB is monitored before exercise (top trace)
The subject is asked to raise the toes as strong as possible against resistance during 10 seconds
After completion of the exercise, the subject is instructed to completely relax while CMAP are recorded at rest :
2 seconds immediately after cessation of exercise (second trace)
and then every 7-8 seconds for 50 seconds (traces 3-8 on the screen)
This sequence (10 s contraction - 50 s rest) is repeated three times

17. Long exercise test (IV)
Back to the right hand for recording CMAP of the ADM at 15 minutes rest after exercise cessation.
If an amplitude decline appeared, it must be carefully checked that nerve stimulation is still supramaximal

18. Needle Electromyography
EMG recording of 5 muscles at rest and during voluntary contraction :
Deltoid
Extensor digitorum brevis
First interosseus dorsalis
Tibialis anterior
Vastus medialis
Searching for myotonic discharges :
Abundant in myotonic syndromes
Rare and inconstant in Hyperkalemic Periodic Paralysis
Absent in Hypokalemic Periodic Paralysis

19. End of the long exercise test (V)
Back to the right hand for recording CMAP of the ADM at 20, 25, 30, 35, 40 minutes rest after exercise cessation.
Changes in CMAP amplitude between -20 and +10 % of the pre-exercise value can be considered normal.
If an amplitude decline appeared, it must be carefully checked that nerve stimulation is still supramaximal

20. End of the long exercise test (V) Changes 20-40 minutes after exercise in muscle channelopathies
Patients with Paramyotonia Congenita
Progressive disappearance of the immediate post-exercise decline in CMAP amplitude
Patients with Periodic Paralysis
Progressive installation of a marked decline of CMAP amplitude of the right ADM
In some cases, a paralysis of the four limbs occurs during the post-exercise rest, with marked CMAP amplitude declines not only of the right ADM, but also of the left ADM and of the EDB.

21. Conclusion Total duration of the protocol realization : 50 minutes
Preparation : 5 mn; Long exercise : 5 mn; Rest after long exercise with repeated short exercises and needle EMG : 40 mn
By comparing EMG findings and responses to long and repeated short exercise tests, five main patterns of muscle abnormalities could be defined (Type I-V), each of them corresponding to a defined group of ion channel mutations.
References for the results :
Fournier et al. Annals of Neurology, 2004, 56:
Fournier, Rev Neurol (Paris), 2005, in press

22. Ackowledgments
Thanks to Ghislaine Therme for technical assistance and Nicolas Danziger for filming and comments.
This video tape was ordered and supported by Periodic Paralysis Association.
The work on muscle channelopathies was supported by Résocanaux and Association Française contre les Myopathies (AFM).