Dr Parag MoonSenior resident, Neurology

GMC, Kota

Motor study -Ipsilateral to most symptomatic side

1. Median nerve- recording APB stimulating wrist and anticubital fossa.

2. Ulnar nerve- recording ADM stimulating wrist, below and above elbow.

3. Ulnar nerve-recording FDI stimulating wrist, below and above elbow.

4. Peroneal nerve-recording EDB stimulating ankle, below fibular neck,lateral popliteal fossa

5. Tibial nerve-recording AHB stimulating ankle, popliteal fossa.

Sensory study

1. Median SNAP

2. Ulnar SNAP

3. Radial SNAP

4. Sural SNAP

Late responses

1. F response

2. H reflexes

Contralateral motor studies done if predominatly LMN signs without definite UMN signs.

Proximal stimulation done if predominatlyLMN signs with normal routine motor study with abnormal late responses.

Amplitude ratio of APB/ADM and FDI/ADM.

APB/ADM <0.6

FDI/ADM <0.9

If both ratio are abnormal, highly suggestive of ALS.

Limb muscles Sample atleast 3 limbs Distal and proximal muscles Muscles with different root innervation Thoracic spinal segment Sample atleast 3 segments Avoid T11-T12 Bulbar muscles Atleast one muscle

(tongue,masseter,stercleidomastoid,facial )

ALS defined electrophysiologically by active denervation and reinervation in three out of four body segments(craniobulbar, cervical, thoracic, lumbosacral)

That cannot be explained by multiple mononeuropathies or radiculopathies.

Neuropathic changes -muscles innervated both by different nerves that share same myotome and by different myotomes.

Definite- 3 region with UMN and LMN features

Probable-2 region with UMN and LMN features with few UMN features rostral to LMN

Possible-1 region with UMN and LMN features or UMN features in 2 regions

1.Sensory potentials-lateral antebrachialcutaneous, radial, median, ulnar, medial antebrachial cutaneous

Compare with unaffected side

2.Median nerve- recording APB stimulating wrist and anticubital fossa.

3.Ulnar nerve- recording ADM stimulating wrist, below and above elbow.

In suspected lower trunk/median cord injury median and ulnar motor study also stimulated at axilla and Erbs point

Proximal median conduction study, collision techniques can be used

Compare with unaffected side

Suspected upper/middle trunk lesion-stimulating Erbs point recording biceps, triceps, deltoid, supraspinatus, infraspinatus

SNAP Cord Trunk

Lateral antebrachialcutaneous

Lateral Upper

Radial to thumb Posterior Upper

Median to thumb Lateral Upper

Radial to snuffbox Posterior upper/middle

Median to index finger Lateral Upper/middle

Median to middle finger

Lateral Middle

Median to ring finger Medial middle/lower

Ulnar to ring finger Medial Lower

Ulnar to little finger Medial Lower

Dorsal ulnarcutaneous

Medial Lower

Medial antebrachialcutaneous

Medial Lower

Atleast 1 muscle in each peripheral nerve distribution

All clinically weak or paralysed muscles should be examined

Proximal muscles including paraspinalmuscles

Upper trunk lesion examine rhomboids and/or serratus anterior

If finding equivocal or borderline compare with other side

Nerve Muscles

Median Pronator teres,APB

Anterior interosseous Flexor pollicis longus

Posterior interosseous Extensor indicis proprius, extensordigitorum communis

Ulnar FDI, flexor digitorum profundus

Radial Extensor carpi radialis,brachioradialis, triceps

Axillary Deltoid

Musculocutaneous Biceps

Suprascapular Supraspinatus, infraspinatus

Dorsal scapular Rhomboids

Dorsal rami Cervical paraspinal

Routine studies

1. Median motor study recording at APB stimulating at wrist,anticubital fossa

2. Ulnar motor study recording at ADM stimulating at wrist, below and above elbow

3. Median and ulnar F waves

4. Median sensory recording digit2 or 3

5. Ulnar sensory recording digit 5

6. Radial sensory recording snuffbox

Highly suggestive of CTS if

Median study shows prolonged distal motor and sensory latencies

Prolonged minimum F wave latencies

Median CMAP and SNAP amplitudes may be reduced

Ulnar motor, sensory and F wave studies are normal

Radial sensory response is normal.

1. Median vs ulnar palm to wrist mixed nerve study

Stimulating median nerve in palm on line connecting median nerve in middle of wrist to web space between 2 and 3 digit

Ulnar nerve stimulated in palm on line connecting ulnar nerve to web space between 4 and 5 digit

Recording electrodes at median and ulnarnerve

Distance between electrodes=8 cm

Antidromic technique

Recording ring electrodes placed over 4th

digit

G1 over metacarpophalengeal joint

G2 over distal interphalengeal joint

Median and ulnar nerves stimulated one at a time at wrist

Difference in onset or peak latencies noted

Active electrode(G1) slightly distal and lateral to midpoint of third metacarpal

Reference electrode over proximal interphalengeal joint of 2nd digit

Stimulation at wrist for median and ulnarnerve

Difference between distal latencies is compared

Begins 4 cm proximal to distal wrist crease, continues 6cm distal to wrist crease

Segmental stimulation at 1 cm increments

For each 1 cm increment latency usually increases 0.2 to 0.3ms

Limitation- difficulty in stimulation just distal to wrist crease

G1 over metacarpophalengeal joint of 1st digit

G2 over interphalengeal joint of 1st digit

Stimulation at wrist for median and radial nerve equidistant from recording electrodes

Difference between latencies noted

G1 and G2 placed at proximal and distal interphalengeal joint of 3rd digit

Median nerve stimulated at wrist

Stimulated at palm at half wrist to digit distance

Wrist to palm conduction velocity calculated

P to D CV X W to D CV/2P X to D CV -W to D CV

Reversal seen in CTS

1. Abductor pollisis brevis

2. Atleast 2 C6-C7 innervated muscle (pronator teres,flexor carpi radialis, triceps brachi, extensor digitorum communis)

*APB sudy is painful. So best not studied first

If APB is abnormal

Atleast 1 proximal median innervated muscle (flexor carpi radialis, pronator teres, flexor pollicis longus) to exclude proximal neuropathy

Atleast 2 non median lower trunk/C8-T1 innervated muscle(FDI, extensor indicisproprius)

1. Posterior interosseous nerve

2. Radial nerve at spiral grove

3. Radial nerve in axilla

4. Posterior cord of brachial plexus

5. C7 radiculopathy

1. Radial motor study-recording extensor indicis proprius stimulating forearm, elbow, below and above spiral grove, bilaterally

2. Ulnar motor study-recording ADM stimulating wrist below and above groove in flexed elbow position

3. Median motor study-recording APB recording wrist, anticubital fossa

4. Median and ulnar F waves

5. Superficial radial sensory study-recording over extensor tendons of thumb, stimulating forearm, bilaterally

6. Ulnar sensory study-recording 5th digit

7. Median sensory study-recording 2nd or 3rd

digit

1. Posterior interosseous neuropathy(axonal)-normal superficial radial sensory SNAP, low amplitude distal CMAP

2. Posterior interosseous neuropathy (demyelinating)-normal SNAP, conduction block between forearm and elbow,normalCMAP amplitude

3. Radial neuropathy in spiral grove(axonal)-reduced SNAP, reduced CMAP amplitude

4. Radial neuropathy at spiral grove (demyelinating)-normal SNAP, conduction block at spiral groove

5. Radial neuropathy in axilla(axonal)-reduced SNAP, low amplitude CMAP

6. Radial neuropathy at axilla (demyelinating)-normal SNAP, normal motor study above spiral groove

7. Superficial radial sensory neuropathy-reduced SNAP, normal radial motor study

Atleast 2 posterior interosseous innervated muscles(Extensor indicis proprius, extensor carpi ulnaris, extensor digitorum communis)

Atleast 1 radial innervated muscle proximal to bifurcation of main radial nerve distal to spiral groove(brachioradialis,extensor carpiradialis)

Atleast 1 radial innervated muscle proximal to spiral groove(triceps, anconeus)

Atleast 1 non radial posterior cord innervated muscle(deltoid, lattismus dorsi)

Atleast 2 non radial C7 innervated muscle(flexor carpi radialis, pronator teres, flexor digitorum sublimis, cervical paraspinalmuscles)

*Avoid supinator muscle

1. Deep peroneal nerve

2. Common peroneal nerve

3. Sciatic nerve

4. Lumbosacral plexus

5. L5 radiculopathy

Routine studies

1. Peroneal motor study- recording extensor digitorum brevis stimulating ankle, below fibular head, lateral popliteal fossa

2. No conduction block or focal slowing at fibular head then recording at Tibialisanterior stimulating below fibular head, lateral popliteal fossa

2. Tibial motor study recording abductor hallucis brevis stimulating medial ankle, popliteal fossa

3. Superficial peroneal sensory study stimulating lateral calf recording lateral ankle

4. Sural sensory study stimulating calf recording posterior ankle

5. Tibial and peroneal F responses

Routine study

1. Atleast 2 muscles innervated by deep peroneal nerve (eg. Tibialis anterior, extensor hallucis longus)

2. Atleast 1 muscle in superficial peronealnerve( peroneus longus, brevis

3. Tibialis posterior and atleast 1 other tibialinnervated muscle(medial gastrocnemius, soleus, flexor digitorum longus)

4. Short head of biceps femoris

If short head of biceps femoris or any tibialinnervated muscle is abnormal then EMG study of other sciatic muscles, gluteal, paraspinal muscles performed

Thank u

1. Electromyography and neuromuscular disorders: D. Preston, B Shapiro:2013 Elsevier Inc

2. American association of Neuromuscular and electrodiagnostic medicine;Practiceguidelines 2012