Brachial Plexopathy

Diagnosis:

The diagnosis is made based on clinical features supported by neurophysiology (NCS/EMG)

Findings on investigations:

Neurophysiology (NCS/EMG)

SNAP:

  • More sensitive than CMAP
  • Normal conduction velocity and distal latency
  • Decreased amplitude in affected nerve (may be normal initially).

CMAP:

  • Indicates severe injury
  • Decreased amplitude
  • Conduction block distal to Erb’s point (i.e. amplitude is reduced at Erb’s point and increased distally) may occur
  • Slowing of conduction velocity at Erb’s point indicates demyelinating lesion

F-wave: nonspecific
EMG:

  • Fibrillations and Positive Sharp Waves PSW in denervated muscles
  • If reinnervation has occurred: MUAP shows decreased recruitment, long duration, increased amplitude, polyphasia
  • Paraspinal muscles are normal (dorsal rami supply these)
Upper trunk:

SNAP: affected amplitudes

  • Lateral antebrachial nerve
  • Median nerve to 1st digit
  • Radial

CMAP:

  • Musculocutaneous nerve to Biceps
  • Suprascapular nerve to supraspinatus
  • Axillary nerve to deltoid

EMG:

  • Involvement of: supraspinatus, biceps, pronator teres, deltoid, brachial
Middle trunk:

SNAP: affected amplitudes

  • Median nerve to 3rd digit and 4th digit

CMAP:

  • Radial nerve to extensor digitorum communis

EMG:

  • Involvement of: Latissimus dorsi, teres major, extensor digitorum communis, pronator teres, flexor carpi radialis
Lower trunk:

SNAP:

  • Ulnar nerve to 5th digit
  • Medial antebrachial

CMAP:

  • Ulnar nerve to adductor digiti minimi
  • Median nerve to abductor pollicis brevis

EMG:

  • Involvement of: abductor digiti minimi, flexor carpi ulnaris, flexor digitorum superficialis, flexor digitorum
Lateral Cord:

SNAP: affected amplitudes

  • Lateral antebrachial nerve
  • Median nerve to 1st digit

CMAP:

  • Musculocutaneous nerve to biceps

EMG:

  • Involvement of: Biceps, pronator teres, flexor carpi radialis, Pectoralis
  • Sparing of: Suprapinatus, infraspinatus, levator scapulae
Posterior Cord:

SNAP: reduced amplitudes in

  • Radial

CMAP:

  • Axillary nerve to deltoid
  • Radial nerve to extensor carpi ulnaris

EMG:

  • Involvement of: Latissimus dorsi, teres major, deltoid, radial muscles
Medial Cord:

SNAP:

  • Ulnar nerve to 5th digit
  • Medial antebrachial nerve

CMAP:

  • Ulnar nerve to abductor digiti minimi
  • Median nerve to abductor pollicis brevis

EMG:

  • Involvement of: Ulnar muscles, flexor digitorum superficialis, flexor pollicis longus, abductor pollicis brevis,

Investigations to consider:

  • CT neck and thorax: cervical rib
  • MRI brachial plexus,
  • NCS/EMG: rule out radiculopathy

 

Causes of brachial plexopathy:

Compressive/traumatic/radiation:

Immune:

Infectious:

  • Herpes Zoster plexitis, neuritis and ganglionitis

Neoplastic:

Hereditary:

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