Brachial Plexopathy Flashcards
Clinical patterns of brachial plexopathies?
- Panplexus
- Upper trunk plexopathy
- Middle trunk plexopathy
- Lower trunk plexopathy
- Lateral cord plexopathy
- Posterior cord plexopathy
- Medial cord plexopathy
Describe panplexus brachial plexopathy!
A complete brachial plexopathy results in weakness, sensory loss, and decreased or absent reflexes in the entire arm.
Provided the roots remain intact, the serratus anterior (long thoracic nerve - C5-7) and rhomboids (dorsal scapular nerve - C5) are usually the only muscles spared because they are innervated by nerves that comes directly off the roots, proximal to the plexus.
The assesment of these two muscles is often KEY, BOTH clinically AND electrically, in differentiating a severe lesion at the level of the plexus from one originating at the roots.
Describe upper trunk plexopathy!
The upper trunk is formed from C5-6. Thus the most affected muscles are supraspinatus, infraspinatus, deltoid, biceps, and brachioradialis.
Muscles that received partial upper trunk innervation such as pronator teres (C6-7), flexor carpi radialis (C6-7), tricep (C6-8), extensor carpi radialis longus (C6-7), and supinator (C6-7) maybe partially affected.
Sensory loss involves lateral arm (Upper lateral brachial cutaneous nerve - axillary nerve), lateral forearm (lateral antebrachial cutaneous nerve - musculocutaneous nerve), lateral hand and thumb (median and radial nerve).
Biceps and brachioradialis reflexes depressed or absent. Tricep reflex is spared.
Describe middle trunk plexopathy!
Very rare.
Middle trunk formed directly from C7 nerve root only, thus mimics C7 radiculopathy. Weakness primarily involves triceps (C6-8), flexor carpi radialis (C6-7), and pronator teres (C6-7). Finger and wrist extensors might also be involved (C7-8).
Sensory abnormalities predominantly affect middle finger, and less so the index and ring finger (median nerve and Superficial sensory radial nerve), and posterior forearm (posterior cutaneous nerve to the forearm - radial nerve).
Only triceps reflex is abnormal.
Describe lower trunk plexopathy!
Lower trunk is formed from C8-T1 nerve roots.
Involved the entire ulnar nerve, medial brachial and antebrachial cutaneous nerve, and partial median and radial motor innervation.
Motor findings involved all ulnar innervated muscles, C8-T1 median innervated muscles (flexor digitorum superficialis, 1st-2nd flexor digitorum longus, flexor pollicis longus, abductor pollicis brevis, opponens pollicis, 1st-2nd lumbricals), and C8 radial innervated muscles (ECRB, finger extensors).
Sensory loss involves the medial arm (medial brachial cutaneous nerve), medial forearm (medial antebrachial cutaneous nerve), medial hand, 4th and 5th fingers (palmar and dorsal ulnar cutaneous nerve, superficial sensory division of ulnar nerve).
No reflex abnormalities.
Etiology of brachial plexopathy?
- Traumatic brachial plexus injury (most common)
- Neoplasms and other mass lesion
- Neuralgic amyotrophy (brachial plexitis)
- Postoperative brachial plexopathy
- Delayed radiation injury
- Thoracic Outlet Syndrome
In injuries where the head is pushed away from the shoulder (eg. head or shoulder striking the pavement when a person is thrown from a moving vehicle) typically result in what type of brachial plexus injury?
Upper plexopathies, affecting C5-6 fibers. Such injuries result in characteristic weakness of shoulder abduction, elbow flexion, and arm supination, known as Erb’s palsy.
This is the most common type BPI seen in newborns, presumably as the head being delivered down, away from the shoulder.
Injuries in which the arm and shoulder are pulled up typically result in what tpe of brachial plexopathies?
Lower plexopathies, affecting C8-T1 fibers. Such injuries result in severe hand weakness with preservation of upper arm and shoulder girdle muscles, known as Klumpke’s palsy.
Severe traction injuries may result in damage to the roots as well as the plexus. A traction injury can cause frank root avulsion. What is the clinical significance of root avulsion?
Detecting/diagnosing root avulsion in brachial plexus injury is important, because in this type of injury there is no chance of spontaneous recovery. NCS and needle EMG are useful in differentiating root avulsion from plexus lesion.
Types of thoracic outlet syndrome?
- Neurogenic thoracic outlet syndrome (rare, need surgical intervention)
- Disputed thoracic outlet syndrome (quite common, treated conservatively)
- Vascular thoracic outlet syndrome
Etiology of true neurogenic TOS? What is the characteristic clinical findings?
Most cases of true neurogenic TOS are caused caused by a fibrous band that runs from a rudimentary cervical rib to the first thoracic rib, entrapping the lower trunk.
Accordingly the sensory and motor loss develops in the C8-T1 distribution. Anatomically, the fibrous band most often preferentially affect the T1 fibers. This result in a characteristic pattern of symptoms, including prominent wasting and weakness of the thenar eminence, and less prominently the hypothenar muscles. The explanation is not completely clear, but probably because the thenar muscles are more T1 innervated, whereas the hypothenar muscles receive more C8 innervation. Radial C8 weakness (eg. EIP) can occur but is less common
What is the differential diagnosis of neurogenic TOS? How to differentiate clinically between those diagnosis?
- Neurogenic TOS: All three conditions may cause atrophy and weakness affecting the thenar and hypothenar muscles. In neurogenic TOS, thumb abduction (Abductor Pollicis Brevis - APB) is preferentially affected. Sensory abnormalities involve ulnar nerve territory and extend proximally into the medial forearm (medial antebrachial cutaneous nerve)
- Ulnar neuropathy at the elbow: local tenderness and pain around the elbow. Thumb abduction spared (APB - median innervated). Sensory abnormaliites restricted to ulnar nerve territory.
- C8-T1 radiculopathy: History of neck pain radiating down the arm, provoked by neck movement. Thumb abduction may be weak but not out of proportion to weakness of the other C8-T1 muscles.
What are the goal(s) of electrophysiologic study in suspected brachial plexopathy?
- To localize the lesion and asses its severity.
- Exclude the possibility of radiculopathy or multiple peripheral nerve lesions mimicking a BP lesions.
The evaluation of brachial plexopathy relies primarily on the sensory nerve action potentials (SNAPs) and a detailed needle EMG examination. Motor conduction studies, are generally not useful in differentiating between a plexopathy and radiculopathy.
What is the common electrophysiologic pattern of upper trunk plexopathy?
Upper trunk lesions may result in abnormal lateral antebrachial cutaneous sensory responses. In addition, radial and median sensory responses may be abnormal, especially when recording the thumb.
Median and ulnar motor conduction studies and F responses are normal.
Needle EMG abnormalities may involve the deltoid, biceps, brachioradialis, supraspinatus, and infraspinatus muscles. The triceps, pronator teres, and FCR may be partially involved. Rhomboids, serratus anterior, and cervical paraspinal muscles are spared (if no concomitant radiculopathy or root avulsion)
What is the common electrophysiologic pattern of lower trunk plexopathy? What is the difference with medial cord plexopathy?
Lower trunk lesions affect the ulnar, dorsal ulnar, and medial antebrachial cutaneous SNAPs.
Median and ulnar innervated hand muscles CMAP and F responses may be abnormal as well. If axonal loss is present, CMAP amplitude may be reduced, with mild prolongation of distal latency and mild slowing of conduction velocity.
The vast majority of these lesions are axonal rather than demyelinating, so motor conduction study across the BP often are not helpful.
Needle EMG may show abnormalities in all ulnar innervated muscles as well as the median and radial innervated muscles that contain C8 or T1 fibers.
Medial cord lesions are identical to lower trunk plexopathies, except that radial innervated C8 muscles are normal in EMG.
