EMG/NCS for Lower Extremity PNS Diseases

Question 1

sciatic neuropathy

Answer 1

weakness in knee flexion, potentially foot drop, along with sensory abnormalities down the back of the thigh and dorsum of foot
- Essentially weakness in knee flexion +/- ankle and toe mover weakness

NCS:
- Abnormal sural, superficial fibular SNAPs
- Abnormal EDB, AH СМАР

EMG:
- Decreased recruitment, fibs/sharps in all sciatic nerve muscles; polyphasia

Question 2

common fibular neuropathy

Answer 2

foot drop, toe extension weakness, eversion weakness
- Abnormal sensation to entire dorsum of foot and lateral leg

NCS:
- Abnormal superficial fibular and sural SNAPs
- Normal medial and lateral plantar SNAPs
- Abnormal EDB and TA CMAP (?conduction block across fibular head)

EMG:
- Decreased recruitment, fibs/sharps in TA, EHL, EDL, fib longus, fib brevis; polyphasia

Question 3

superficial fibular neuropathy

Answer 3

Eversion weakness with abnormal sensation over lateral leg and dorsum of foot EXCEPT Ist web space

NCS:
- abnormal superficial fibular SNAP

EMG:
- abnormal activity in fib longus and brevis

Question 4

deep fibular neuropathy

Answer 4

Foot and/or toe drop with abnormal sensation over Ist web space of toes

NCS:
- normal superficial fibular SNAP

EMG:
- abnormal activity in TA/EHL/EDL/EDB

Question 5

tarsal tunnel syndrome

Answer 5

Intrinsic foot weakness, abnormal plantar sensation, +Tinel at medial ankle; divides into medial and plantar nerves

Medial plantar nerve
- AH, FDB, FHB, 1st lumbrical; medial plantar sensation

Lateral plantar nerve
- ADQP, interossei, all other lumbricals; lateral plantar sensation

NCS:
- Abnormal medial and lateral plantar SNAPs
- Abnormal CMAP to AH

EMG:
- Abnormal activity in AH, lumbricals, interossei., ADQP

Question 6

femoral neuropathy

Answer 6

Weakness of knee extensors (knee buckling), abnormal sensation to anterior thigh and medial leg (saphenous nerve)

NCS:
- Abnormal saphenous nerve SNAP and femoral nerve CMAP (rectus femoris)

EMG:
- Abnormal activity in quads

Question 7

saphenous neuropathy

Answer 7

Abnormal sensation to medial leg +/- medial knee

NCS:
- Abnormal saphenous SNAP

EMG:
- normal

Question 8

obturator neuropathy

Answer 8

Thigh adduction weakness, abnormal sensation to medial thigh

NCS:
- Normal routine SNAPs (sural, superficial fibular)
- Normal routine CMAPs (EDB, AH)

EMG:
- Abnormal activity in thigh adductors

Question 9

lateral femoral cutaneous neuropathy (meralgia paresthetica)

Answer 9

Abnormal sensation over lateral thigh

NCS:
- Abnormal SNAP of LFCN

EMG:
- normal

Question 10

lumbosacral plexopathy

Answer 10

The lumbar plexus involves the Li-L4 nerve roots
* Anterior division forms the obturator nerve
* Posterior division forms the femoral nerve and lateral femoral cutaneous nerve (L2, L3)
- Saphenous SNAP, LFCN SNAP, femoral nerve CMAP

The sacral plexus involves the L4-S4 nerve roots
* Anterior division forms the tibial nerve
- Sural SNAP, plantar SNAPs, AH CMAP
Posterior division forms the common fibular nerve
- Superficial fibular SNAP, EDB CMAP
* Superior and inferior gluteal nerves directly come off the sacral plexus

NCS:
- Variable abnormalities in SNAPs and CMAPs

EMG:
- Variable abnormal spontaneous activity and recruitment
- Remember, paraspinals are normal in all plexopathies!
- The ventral rami give rise to the plexus, while the dorsal rami innervate the paraspinals

Question 11

diabetic lumbosacral radiculoplexopathy

Answer 11

variable weakness and sensory loss in the lower limbs depending on what parts of the plexus/nerve roots are affected

NCS:
- Abnormal lower extremity SNAPs of affected nerves/roots
- Abnormal lower extremity CMAPs to affected muscles

EMG:
- Abnormal activity in affected lower extremity muscles

Question 12

radiculopathy

Answer 12

NCS:
* Normal SNAPs
* Abnormal CMAPs of muscles belonging to affected nerve roots
- E.g. TA, EDB CMAP will be abnormal in L5 radiculopathy
* Abnormal H reflex in an Sl radiculopathy

EMG:
* Abnormal activity in all muscles innervated by the injured nerve root
* Must needle at least 6 muscles in a “root screen”
* Paraspinals at the affected level will be abnormal
* Must demonstrate abnormalities in 2 muscles that share the same nerve root, but have different peripheral nerve innervations
- E.g. C6 radiculopathy showing abnormalities in PT and BR

Question 13

nerve root avulsion

Answer 13

numbness in affected dermatome, and complete weakness in affected myotome

NCS:
- Normal SNAPs (because lesion is proximal to DRG, so sensory axons are healthy!)
- Absent CMAPs

EMG:
- Abnormal spontaneous activity in muscles of the affected myotome; no recruitment whatsoever
- Abnormal spontaneous activity in affected paraspinals