LE PNS Disease

Question 1

sciatic neuropathy

Answer 1

Hx posterior trauma, posterior hip dislocation, posterior approach hip replacement, tight piriformis

may affect tibial or common fibular n.; usually common fibular fibers (dorsiflexion, eversion)

Px: weakness w knee flexion +/- ankle and toe mover weakness

Question 2

sciatic neuropathy EDX

Answer 2

NCS: abnormal sural (courses posterior leg and around lateral malleolus) and superficial fibular (coruses anterior ankle from common fibular and tibial n.) SNAPs
abnormal EDB (deep fibular n.) and AbH (tibial n) CMAP

EMG: decreased recruitment (machine gun) MUAPs, fibs/sharps in all sciatic n. muscles, polyphasicity

all: esp hamstrings; if normal, lesion may be more distal in common fibular/tibial pathway

Question 3

common fibular neuropathy

Answer 3

injury to common fibular n. (squatting, crossing legs) typically as it wraps around the fibular head → foot drop, toe extension weakness, eversion weakness + abnormal sensation to entire dorsum of foot (except 1st web space) and lateral leg

sciatic n. posterior thigh → tibial and fibular branches → fibular splits to superficial and deep fibular n. →

superficial: fibularis longus, fibularis brevis (plantar flexors and evertors) + sensation to dorsum of foot (except 1st web space) and lateral leg
deep: (anterior compartment muscles) TA, EDL, EHL, EDB

Question 4

common fibular neuropathy EDX

Answer 4

PE: positive Tinel at fibular head

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, EDB, fib longus, fib brevis; polyphasicity

Question 5

DDx superficial v deep fibular neuropathy - PE

Answer 5

superficial fibular n. → lateral compartment → fibularis longus, fibularis brevis → foot eversion weakness; abnormal sensation over lateral leg and dorsum of foot EXCEPT 1st web space

deep fibular n. → anterior compartment → TA, EDB, EDL, EHL → foot drop and weakness with toe extension; abnormal sensation in 1st web space

Question 6

DDx superficial v deep fibular neuropathy EDX

Answer 6

superficial
NCS: abnormal superficial fibular SNAP
EMG: abnormal activity in fibularis longus and brevis

deep
NCS: normal superficial fibular SNAP
EMG: abnormal activity in TA/EHL/EDL/EDB

Question 7

tarsal tunnel syndrome Px

Answer 7

intrinsic foot weakness, abnormal plantar sensation (medial/plantar terminal branches of tibial n.)

PE: +tinel at ankle

Question 8

tarsal tunnel syndrome EDX

Answer 8

NCS: abnormal medial and plantar SNAPs
abnormal CMAP to AH (medial plantar n.)

EMG: abnormal activity in AH, lumbricals, interossei, ADQP

Question 9

femoral neuropathy Px

Answer 9

weakness of knee extensors (knee buckling), abnormal sensation to anterior thigh and medial leg (saphenous n.)

usually d/t diabetic lumbosacral plexopathy; also consider anterior hip dislocation, retroperitoneal hematoma, compression under inguinal ligament

Question 10

femoral neuropathy EDX

Answer 10

NCS: abnormal saphenous n. SNAP and femoral nerve CMAP (rectus femoris)

EMG: abnormal activity in quads

be sure to test obturator (L2, 3, 4) n. muscles: adductor, gracilis → if abnormal, suggests L3 radiculopathy rather than femoral neuropathy

Question 11

L3 radiculopathy v femoral neuropathy - DDx on EDX

Answer 11

test obturator (L2, 3, 4) n. → adductor muscles and gracilis

if abnormal, suggests L3 radiculopathy rather than isolated femoral neuropathy

Question 12

saphenous neuropathy

Answer 12

Hx knee arthroscopy, trauma

courses between vastus medialis and sartorius

Px abnormal sensation to medial leg +/- medial knee

Question 13

saphenous neuropathy EDX

Answer 13

NCS: abnormal saphenous SNAP

EMG: normal

saphenous n. is pure sensory branch for femoral n. (L2, 3, 4)

Question 14

obturator neuropathy

Answer 14

obturator n. (L2, 3, 4) → thigh adductor longus/magnus/brevis inn.

Hx pelvic fx, trauma

adductor weakness + abnormal sensation medial thigh

Question 15

obturator neuropathy EDX

Answer 15

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

EMG: abnormal activity in thigh adductors

Question 16

lateral femoral cutaneous neuropathy

Answer 16

AKA meralgia paresthetica

usually d/t tight inguinal ligament

Hx rapid weight loss, tight belt, obesity

Px: abnormal sensation and burning pain over ovoid patch atnerolateral thigh d/t entrapment/irritation of LFCN

Question 17

LFCN EDX

Answer 17

NCS: abnormal SNAP to LFCN

EMG: normal

Question 18

lumboscaral plexopathy v radiculopathy

Answer 18

EMG paraspinals (solely inn’d by dorsal rami of lumbosacral plexus) → if abnormal, suggests radiculopathy

ventral rami of L1-S4 → lumboscaral plexus

Question 19

lumbosacral plexopathy EDX

Answer 19

variable findings

paraspinals normal (inn’d by dorsal rami)

ventral rami → plexus

Question 20

radiculopathy EDX Dx pearls

Answer 20

NCS: normal SNAPs - injury is proximal to DRG and we are testing peripheral nerves distal to DRG
abnormal CMAPs to muscles belonging to affected n. roots
abnormal H1 reflex in S1 radiculopathy

EMG: abnormal activity in all muscles inn’d by injured n. root

1. must test 6 muscles in a “root screen”
2. paraspinals at affected level will be abnormal; v normal in plexus injury (injury distal to n. roots)
3. must demonstrate abnormalities in 2 muscles that share same n. root but have diff peripheral n. inn (e.g., C6 radiculopathy showing abnormalities in PT (C6,7 → median n.) and BR (C5, 6 → radial n.)

Question 21

n. root avulsion

Answer 21

tearing off n. roots d/t trauma, very poor prognosis bc n. must grow all the way down extremity, won’t realistically happen

p/w numbness in affected dermatome and weakness in affected myotome

NCS: normal SNAPs, absent CMAPs
SNAPs normal bc peripheral axon is still intact

EMG: abnormal spontaneous activity in muscles of affected myotome + abnormal spontaneous activity in affected paraspinals