Musculocutaneous neuropathy

MN can occur proximally where it painlessly affects biceps strength and sensation in the forearm or more distally near the elbow where is is purely a sensory syndrome accompanied by pain. Heavy physical activity with resistive movements of the upper extremity is the usual inciting factor, although it can occur with anterior shoulder dislocation and traumatically (gunshot or stab wound or secondary to surgery). Rest is the treatment and the prognosis is good.

The distal syndrome is due to compression of the lateral antebrachial cutaneous nerve near the biceps aponeurosis with strenuous activity with the arm hyper-extended or the forearm pronated. It is reported in racket sports, windsurfing and swimming. It also occurs after venipuncture, catheterization and placement of an av fistula. Surgery in the antecubital fossa and arm splinting can be responsible. So can pressure of a strap across the elbow or arm restraints. Clinical presentation is numbness and dysesthesias in radial-volar forearm and elbow pain that resembles lateral epicondylitis. Elbow flexion from biceps is absent although the brachioradialis muscle can compensate somewhat. Biceps tendon jerk is absent. Initial treatment is conservative and may involve local steroid injection although decompresive surgery is often necessary.

Nerve is often involved in combinations of axillary, radial, and suprascapular neuropathies or ABN (acute brachial neuritis). Differential-- in biceps rupture, there is not sensory loss, and the biceps muscle contracts into a small bal. With a C6 radiculopathy, there will be involvement of supra/infrapinatus, deltoid and brachioradialis. C6 sensory signs often extend into the hand, whereas lateral cutaneous nerve of forearm stops at the wrist. Surgical exploration can show the distal syndrome due to biceps aponeurosis in patients lacking another clear cause.

Radial/PI neuropathy

Proximal RN may be compressive or traumatic. It can be due to fracture of the humeral shaft and strenuous activity such as weightlifting. It can be due to crush or twisting injury of the wrist or forearm or repetitive pronation and supination at work. Intoxicated individuals sleep with their arm over a bench "Saturday night palsy" with injury to the spiral groove with or without fracture of the humerus. In newborns, the umbilicus can entrap the nerve. These lesions are triceps sparing. Nerve injury at axilla from improper crutches use affects the triceps and the triceps reflex. Fractures of the head of the radius affect the nerve more distally. Compression of the epicondylar branch is one of the types of tennis elbow. Pain and tenderness in the lateral elbow occurs, resembling lateral epicondylitis (another entity known as tennis elbow).

The clinical presentation of proximal RN is wristdrop, inability to extend the fingers, weakness of the brachioradialis and variable sensory loss in the first dorsal web space. If proximal enough it may affect triceps and posterior arm sensation. Athletes should have x rays to exclude fracture. Treatment is conservative including a wrist splint, with surgery reserved for cases that have not improved by four months. SUPERFICIAL RN in forearm can be caused by repetitive pronation/supination maneuvers. The presentation is paresthesias over forearm, wrist, thumb, and dorsal hand, maximal in with wrist flexed in ulnar deviation. Reduced SNAP over the dorsum of hand is seen. Local injection can be used to confirm diagnosis. Treatment is rest, and if unsuccessful, then surgical exploration. Tight watchbands and handcuffs can also cause this (the latter with or without median and ulnar sensory effect). In the forearm, the radial nerve divides into a superficial sensory branch and a deep motor branch (posterior interosseous nerve). Compression of the latter can produce two distinct clinical syndromes: the radial tunnel syndrome (RTS) and and posterior interosseous nerve syndrome (PINS). It can develop after injury to the elbow, or in RA with tenosynovitis. Involvement of the nerve between the two heads of the supinator at the arcade of Frohse causes weakness of the wrist and digit extensors with sparing of the supinator. EMG findings are in the ECR longus and brevis. The differential diagnosis is tendon rupture. PINS can be caused by a local compressive lesion or repetitive pronation-supination or fracture of the proximal radius. It has a 2:1 male predominance. It manifests as painless weakness without sensory loss of affected muscles, rarely with poorly localized pain or dysesthesias. The hand will deviate radially at the wrist with fingers flexed at the metacarpophalangeal joint without wristdrop. The supinator is spared. NCS excludes partial radial neuropathy. X ray excludes compressive lesions. Therapy is conservative with a long arm splint for immobilization. Surgery can be considered after 12 weeks. RTS is usually seen in the dominant arm of patients with repetitive pronation/supination either on the job or in racket sports. The clinical presentation is aching pain of the elbow and forearm without weakness, but in contrast to PINS there may be numbness in the first dorsal web space. It may be confused with lateral epicondylitis (tennis elbow). Provocative tests (nonspecific) include resisted forearm supination and the middle finger test. The patient extends the elbow and holds the middle finger in extension against a force applied to the dorsum of the hand. Diagnosis can be helped by selective injection into the lateral epicondyle or the radial tunnel. A three month trial of rest, splinting and NISAA's usually is sufficient. Steroid injections and surgery are other resorts.

Ulnar neuropathy at elbow and distal

UN at elbow can occur during repetive stress, more commonly with certain positions and decreased body mass, and more commonly in men. Associations exist with overhead throwing sports, cross country skiing, weight lifting and racket sports. One third have no cause. Among athletes it often accompanies other elbow problems including attenuation of the ulnar collateral ligament and medial epicondylitis. The clinical presentation is sensory ulnar in non-athletes but athletes tend to have medial epicondyle pain first. Evaluation requires X rays, +/- ultrasound and MRI. Conservative treatment is rest, splinting, NSIAD's, NOT steroid injection. Surgery is for those with mild/moderate pain who fail conservative therapy,or intractable pain or fixed sensory deficits or weakness. Distal ulnar neuropathy can occur at wrist proximal to, within, or beyond Guyon's canal. The first spares the dorsal ulnar cutaneous branch, the second all cutaneous branches, and the third all but the superficial sensory branches of the fourth and fifth digits. It affects cyclists, wheelchair athletes, racket and club sports. NCS help; therapy is conservative unless there is a fracture such as the hamate. Sensory symptoms in the forearm suggest brachial neuritis rather than ulnar neuropathy. Pitfalls in examination: if nerve conductions appear to show an ulnar conduction block, check for a Martin Gruber anastamosis. Fibers destined for FDI/APB/ADM may travel with median nerve at elbow in about 20 percent of patients. Stimulate the median nerve at the elbow and wrist, and if you get a response only at the elbow you have proved that an anastamosis exists. Another pitfall of nerve conduction is muscle artifact seen with antidromic stimulation (G1 is close to ADM). Solve this problem by doing orthodromics. Another pitfall is brachial neuritis masquerading as an ulnar neuropathy. Medial antebrachial cutaneous nerves are abnormal in cases of lower trunk lesions. It also puts the lesion away from a radiculopathy if abnormal. Distribution of sensory nerve fibers in hand: 100 % of ulnar fifth fibers comes from lower trunk. In index finger 100 % comes from middle or upper trunks (80/20). In thumb, 100 % come from upper trunk. Localizing a true ulnar neuropathy with, one must know common compressions are in retrocondylar groove (most common), humeroulnar arcade (Cubital tunnel), and less commonly, at exit from FCU. Other sites are Guyon's canal, deep ulnar in hand, and (proximally) axilla nd arcade of Struthers. A nerve conduction of dorsal ulnar response recorded between the fourth and fifth metacarpals, 8 cm proximal to wrist,compared to the contralateral side, is useful to differentiate between an ulnar neuropathy at the elbow and wrist. If its normal, it suggests the problem is at the wrist. The Mayo protocol is antidromics from the fifth digit, recorded11 cm proximal to wrist, above and below the elbow velocities. If velocities are <> 20 %, stimulate below elbow and upper arm. If slowing is > 8 mps or 10 % amplitude difference across the 10cm elbow segment, perform 2 cm inching. IF FDI is weak consider FDI recording. Elbow should be flexed at 90 degrees during test. Needle examination should include FDI, ADM, FDP and FCU. FCU is reached in the forearm. It flexes the wrist with ulnar deviation. However FCU may comes off either before or after cubital tunnel. The FDP comes off only after (to digits 4 and 5 is ulnar). Reach by supinating arm, wrist up, 4 finger breadths up, just ulnarly to the shaft. The ulnar fibers are superficial. he flex the dip of the 4th and 5th digits. Both FCU and FDP are C8-T1. If ulnar muscles are abnormal, check APB (C8 median) , EIP (C8 radial), and contralateral FDI. If other C8 muscles are abnormal, check paraspinals. ECU is posterior interosseous (radial) c 6-8, lower trunk extends wrist with ulnar deviation. Do if suspect lower trunk. If the lesion is in the wrist, proximal to Guyon's canal, all ulnar hand muscles will be affected, plus the antidromic DL will be prolonged with a reduced amplitude, with a normal dorsal ulnar response. Sensory loss will exist in an ulnar hand distribution. Proximal to the hypothenar branch, FDI/ADM affected, normal sensory, abnormal hypothenar EMG, normal sensation, weak interossei, lumbricals and hypothenar. Isolated deep branch in the hand, has weak interossei, lumbricals, spares ADM and sensation, reduced FDI amplitude, normal antidromic ulnar sensories, abnormal needle emg in interossei and lumbricals. Reach the latter by going to the second palmar crease, just proximal to joint, just radial to the tendon. Go too deep you'll be in opponens digiti minimi.

Dorsal scapular neuropathy

It entraps the nerve and scapula wings on wide abduction of the arm (like trapezius neuropathy and unlike LT nn wherin its worse with arm outstreched forwards). There may be pain in C5-6 distribution. EMG abnormalities are restricted to levator scapulae, rhomboids major and minor.

Cervical radiculopathy

Levels involved: C5 (6.6%), C6 (17.6%), C7 (46 %) C8 (6.3%) Most usual NCS are C8T1; C5-6 NCS (musculocutaneous/biceps) and C7 (radial EDC) are uncommonly studied. CMAPs should be normal unless there is severe axon loss. Other nerves that can be studied are lateral antebrachial (C5), median recording at index or thumb (C6), median recording at middle finger (C7) or ulnar at ring/little finger (C8) or median antebrachial (T1). Contrary to popular belief, paraspinal muscles are abnormal in only 50-70 % of radiculopathies. Planning the EMG (below) the muscles associated with radiculopathy at the variousl levels are indicated, in order of the chances of their being abnormal. C5. Clinically presents with weak deltoid and infraspinatus. Check deltoid, infrapinatus, biceps, then less often, brachioradialis and rhomboids (rhomboids are usually SPARED). Reach INF with arm abducted at ninety degrees, insert needle 2 finger breadths below the spine of the scapula. Reach rhomboid major on vertebral border of the scapula, from the root of the spine of the scapula to the inferior angle. Patient's hand is at side, test by raising hand from small of the back. Pitfall: if superficial needle will be in trapezius; if deep, in the erector spinae. Rhomboideus minor is just above major with needle insertion one finger breadth medial to vertebral end of the scapular spine with same activation. Pearl: Check pronator teres (C6) to rule out C6 involvement. Reach pronator teres two finger breadths distal to the midpoint of a line connecting the medial epicondyle and the insertion of the biceps tendon. C6 presents with paresthesias into thumb and forefinger; weak biceps and wrist extensors. Abnormal muscles are pronator teres (median C6), deltoid, biceps, triceps, ECR ( upper trunk radial C6). Reach ECR 2 fingerbreadths distal to the lateral epicondyle. It dorsiflexes the wrist in radial deviation. C7 causes paresthesias in forearm and dorsum of hand; weak triceps, long finger flexors and finger extensors. This is the most common radiculopathy. Use multiple nerve distributions. Abnormal muscles are triceps, PT, ECR, EDC and FCR (median all trunks C6-8). Find FCR 3-4 fingerbreadths distal to the midpoint of a line connecting the medial epicondyle and biceps tendon; it flexes the wrist with radial deviation. Other muscles nearby (can hit accidentally) are FDS (deep), FPL (deeper) PT (lat) palmaris longus (medial). Radial artery, FPL and FCR make up "radial trio." Its important to get PT or FCR as a median contributor. C8 involves paresthesias in the little finger and weak intrinsic mm of hand and wrist flexors. Check (in order) FDI, APB (median), FPL, EIP, EDC, TRI, PT, ADM. Pitfalls: ulnar and medial antebrachials should be normal. Consider ALS. Find FPL in middle of the forearm with hand supinated, flexes DIP of thumb. Favors radiculopathy: Pain proximally, in neck or with movement of the neck, along the scapula or the precordial border; pain with coughing, sneezing, or Vasalva maneuvers;

Upper extremity

Root
Clinically Relevant Gross Motor Function
C5
Shoulder abduction; ± elbow flexion
C6
Elbow flexion, pronation/supination, ± wrist extension
C7
Diffuse loss of function in the extremity without complete paralysis of a specific muscle group
C8
Finger extensors, finger flexors, wrist flexors, hand intrinsics
T1
Hand intrinsics

Lumbosacral radiculopathy

LS is more frequent than cervical, and is more common to have involvement of multiple roots. The L5 root is most common (40 %) then S1 (26 %) then L4 (19%) then L3 (16 %). Beware of diabetes mimicking a radiculopathy. Nerve conductions are not that helpful nor is SEP. Needle EMG is best. Below with each root is the order of findings of muscle abnormality at each level, in order, with instructions how to reach some of the muscles listed. L3- ADD, ILI, RF, VL, VM (first two were abnormal in almost all) L4- VM, AT, VL , RF, ADD (percentages were not much more than 50 on most of these) L5 AT (27/40), PER (22/25), FDL (20/25), PT (10/12), GME (25/35), TFL (half) and then almost always normal were RF, VL, GMA, MG (7/40) S1 PER (7/11 was best), GME PT GMA MG AT (5/26) very rarely if ever: VL RF ADD ILI. Paraspinals are very important and are slightly better than the cervicals. Finding muscles: insertion and action ILI insert 2 fingerbreadths lateral to femoral artery and 1 fb below inguinal ligament; flex thigh RF insert anterior thigh, midway between superior border of patella and anterior superior iliac spine. TFL (sup gluteal n, L4) insert 2 fingerbreadths anterior to greater trochanter; abduct thigh VL -- lateral thigh, one handbreadth above patella ; lift heel with knee extended. VM-- 4 fb proximal to sup-med angle of the patella. Lift heel with knee extended. GMA- insert one to three inches midway between greater trochanter and sacrum; extend knee with hip flexed. GME- one inch distal to midpoint of iliac crest; abduct thigh. ADD-- 4 fb distal to pubic tubercle , adducts limb.

ALS Diagnootic Criteria

EMG's decreased recruitment, unstable MUPs, fasciculations, fibrillation potentials, polyphasiscs, increased amplitude and duration. NCS show low amplitude CMAPs which are related to disease severity and prognosis. Ulnar stimulation at Erb's point is necessary to look for conduction block. EMG muscle selection should be done to minimize sticks. Need to see decreased recruitment large MUPs and fibs in at least three levels. Thoracic paraspinals are typically abnormal (80 % quoted) and are useful if coexisting cervical paraspinal abnormalities are seen. EL Escorial Criteria (replaces prior Lambert criteria which were more stringent). There are 4 body regions: bulbar, cervical, thoracic and lumbar. Definite ALS requires denervation in 3 of 4 levels; probable, 2 levels, possible 1 level; suspected 2 levels without UMN signs. In each level, at least two muscles of different spinal nerve, and peripheral nerve innervation should be tested.