Neurophysiological Diagnosis of Birth Brachial Plexus Palsy Dr Grace Ng Department of Paed PMH
Brachial Plexus Anatomy
Brachial Plexus Cords Medial cord: motor and sensory conduction for median and ulnar nerves Posterior cord: radial sensory and needle EMG Lateral cord: musculocutaneous nerve and biceps muscle
Brachial Plexus Anatomy
Evaluation of Brachial Plexus Lesions Neuroimaging - preganglionic spinal root lesion vs postganglionic brachial plexus lesions - MRI of nerve root avulsion: pseudomeningocele - CT-myelography: brachial plexus /nerve root lesion
Pseudomeningocele
Pseudomeningocele
Electromyography Establishing the level and extent of plexus involvement Identifying the presence of a preganglionic lesion or root lesion Defining the nature of the lesion: neurapraxia, axonotmesis or neurotmesis
Preganglionic Root Avulsion Paraspinal muscle denervation: technically challenging in neonates Preservation of sensory nerve action potential (SNAP) in the absence of any clinical sensory function Difficulties: - hard to determine sensory loss - conjoint preganglionic & postganglionic components - specific cervical level hard to comment due to segmental overlap
Difficulties Wide range of normal amplitudes for CMAPs & SNAPs median and ulnar mixed nerve action potentials assessing axonal loss in infants Motor CMAP amplitude disappear within 4-5 days complete axonal disruption in older child Disappearance of SNAPs up to 10-11 days in adult Neither of these temporal relationships established for young infants
Needle EMG Assess the brachial plexus injury Axonal damage despite relatively normal CMAPs and SNAPs Fibrillation potentials/positive waves 10-14 days in older child similar to adult Very few studies on neonates and infants - positive waves as early as day 4 postinjury: i. the short distance from site of injury ii. immature or poorly myelinated nerves Early denervation & EMG patterns: prenatally occurring lesion
Fibrillation potentials
Positive waves
EMG and Timing of the onset of plexopathy Early postpartum denervation- a case report: - shoulder dystocia, macrosomic baby with Erb-Klumpke palsy and Horner s syndrome - D4: no CMAPs or SNAPs but - D4 positive waves in deltoid, biceps, wrist extensors and first dorsal interosseous in D5-3 weeks: pseudomeningocele at C6/C7 Acute signs of denervation occur earlier in neonates
EMG and Timing of the onset of plexopathy Johnson et al: EMGs of 11 infants with OBPP: D4 no fibrillation potentials Clay: 9 week infant with lesion due to osteomyelitis; denervation potentials D10 to D12 Intrauterine onset: peroneal mononeuropathy noted at birth had fibrillation potentials in peroneal innervated muscle at 18 hour of age
Role of EMG in determining prognosis and need for surgical repair Controversial EMG provides information about nerve pathophysiology: nerve root avulsion pre or post-ganglionic lesion upper versus lower or combined lesion Small subgroup with OBPP who lack any functional return at 4 mos: EMG showed neurapraxic lesion with conduction block full recovery by 1 st birthday with conservative approach
CASE REVIEW (1) M FT VE BW 4.15kg Fracture clavicle, reduced R UL movement since birth, good recovery 4 mo: Normal nerve conduction study EMG: reinnervation pattern present at right deltoid and biceps muscles
CASE REVIEW (2) F, FT NSD BW 3.75kg Shoulder dystocia Left Erb s palsy with poor recovery Noticed decrease LUL at birth Decreased finger movement which subsequently has improved No fracture clavicle Seen at 1mo: LUL in erb s palsy, no active shoulder mvement, no biceps contraction, wrist, thumb and fingers in flexion, strong finger flexion
Case review (2) 2 mo NCS: left median and ulnar nerves showed axonal loss, F-wave mprolonged, sensory nerve study normal EMG: re-innervation at left deltoid and triceps. No MUAP at the left biceps and extensor digitorum
6mo: active deltoid fair, strong triceps contraction, active biceps contraction palpable but no elbow flexion, active finger and wrist extension EMG at 6 mo: Re-innervation present at Lt deltoid, Lt triceps, Lt biceps brachii & Lt extensor digitorum communis
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