Erb's palsy

# Overview
Duchenne-Erb's palsy or simply Erb's palsy, is a lesion to the C5-C6 brachial roots; it can be a form of brachial plexus birth palsy (BPBP) or can be acquired in adulthood. It occurs when there is a stretching of the superior brachial plexus (neuropraxia, neuroma, neurotmesis), leading in most of the cases to a temporal weakness and loss of sensation in certain muscles of the upper extremity.

# Historical Perspective
- Erb's palsy, was first described by William Smellie, a British obstetrician, in 1754 on his midwifery book, "Traite de la theorie et pratique des accouchemens".
- In 1861, French neurologist, Guillaume Benjamin Amand Duchenne was the first to discover the association of paralysis in the same muscles (deltoid, biceps, and subscapularis) of arms and shoulders of infants delivered vaginally, naming it "obstetric palsy of the brachial plexus".
- In 1874, German neurologist, Wilhelm Heinrich Erb concluded that paralysis was associated with a radicular lesion at the level of the superior plexus, C5-C6, and not from isolated peripheral nerve lesions.
- In 1985, Narakas made a classification for Erb's palsy grading the severity and determining the prognosis.

# Classification
- Erb's palsy may be classified according to the severity of damage produced to the brachial plexus nerves as:
- Neurapraxia: Mild, temporal disruption, or compression of the myelin sheath, with no structural damage to the axon.
- Axonotmesis: Anatomic interruption of the myelin sheath and the axon of the nerve, but perineurium and epineurium remain intact.
- Neurotmesis: Complete tear of the nerve, including the axon with his endoneurium, perineurium, and epineurium.
- Erb's palsy, in turn, is also classified within the Narakas system, which categorizes Brachial Plexus Birth Palsy (BPBP) according to the roots involved, and its directly linked to its prognosis:
Group I: Classic Erb's palsy (C5-C6 roots). Good spontaneous recovery in > 80% of cases.
Group II: Extended Erb's palsy (C5-C7 roots). Good spontaneous recovery in > 60% of cases.
Group III: Global palsy without Horner syndrome (C5-C8 roots). Good spontaneous recovery of shoulder/elbow in > 3050% of cases. Functional hand frequently noted.
Group IV: Global palsy with Horner syndrome (C5-T1). Without surgery, severe arm deficits are expected.
- Group I: Classic Erb's palsy (C5-C6 roots). Good spontaneous recovery in > 80% of cases.
- Group II: Extended Erb's palsy (C5-C7 roots). Good spontaneous recovery in > 60% of cases.
- Group III: Global palsy without Horner syndrome (C5-C8 roots). Good spontaneous recovery of shoulder/elbow in > 3050% of cases. Functional hand frequently noted.
- Group IV: Global palsy with Horner syndrome (C5-T1). Without surgery, severe arm deficits are expected.

# Pathophysiology
- Erb's palsy is caused by damage to the upper brachial plexus, cervical roots C5-C6, and in 50% of the cases, involving C7.
- Although, damage can occur at any time, this usually happens during a delivery complicated by shoulder dystocia.
- Excessive upper traction to the baby's head in opposite direction from the shoulder produces stretching to the nerve fibers that can lead to a simple temporal disruption or compression, to a complete tear of the entire plexus.
- Another way of damage to upper brachial plexus can be made by excessive pressure on the baby's raised arm during a breech delivery. 
- The superior trunk of the brachial plexus has a motor and sensory fibers. Palsy of C5 and C6 roots affects the movement of deltoid, biceps, brachialis, infraspinatus, supraspinatus, and serratus anterior muscles, as well as the sensation of the skin of the shoulder, anterolateral forearm, index and thumb fingers.
- Consequently, the patient is unable to abduct or externally rotate the shoulder, as well as supinate the forearm because of weakness.

# Causes
- The most common cause of Erb's palsy is a difficult extraction during vaginal delivery due to shoulder dystocia. To review the risk factors that aim into a difficult extraction, and ultimately promote Erb's palsy, click here.
- In adults, the most frequent causes are motor vehicle accidents (>90% of cases), work-related trauma (industry), severe fall with stretching of the neck, assault (knife or bullet injury), and iatrogenic injury (surgery).

# Differentiating Erb's palsy from other Diseases
Erb's palsy must be differentiated from:
- Klumpke palsy. Presents with "claw hand" and negative grasp reflex, many times accompanied by Horner's syndrome.
- Clavicular fracture. Presents with visible swelling, and deformity in the clavicular region, as well as crepitation and a positive "piano key sign".
- Osteomyelitis of the humerus or clavicle. Presents with high WB cell count, and osteolysis on plain radiograph.
- Septic arthritis of the shoulder. Presents with soft tissue edema of the shoulder in an MRI.
- Spinal cord or brachial plexus tumor. Presents with a bulging mass in the shoulder, and many times, is associated with neurofibromatosis type II.

# Epidemiology and Demographics
- The prevalence of Erb's palsy is approximately 90 to 206 per 100,000 in the United States, while prevalence worldwide is approximately 50 to 500 per 100,000 individuals.
- An incidence of 36-45 per 100,000 births has been reported for Erb's palsy in the US.
- There is a greater prevalence of right arm Erb's palsy over the left side, with a rate of 1.3:1 to 7:1, with only 3% affecting both arms.
- Permanent impairment occurs at a rate of 3-25% of patients with Erb's palsy.
- In 2007, a study made by Weizsaeker et al found that African descendants had an independently higher risk for Erb's palsy.
- Mothers age greater than 34 years old, were found to be more prone to have a child with Erb s palsy.
- Females seem to be slightly more affected by Erb's palsy in brachial plexus birth palsies than males, while this proportion greatly inverts in adulthood, with more accidents occurring in males.

# Risk Factors
Common risk factors for neonatal Erb's palsy involve maternal, fetal, and labor factors:
1. Mothers risks:
- Maternal diabetes
- Maternal obesity
- Shoulder dystocia in prior deliveries
2. Fetal risks:
- Breech presentation
- Macrosomia
3. Labor risks:
- Shoulder dystocia
- Oxytocin use
- Prolonged labor (second stage of labor > 60 minutes)
- Difficult extractions (need for forceps or other operative measures)
Studies have shown that these typical risk factors are not reliable predictors for Erb's palsy. Furthermore, the majority of Erb's palsy newborns have come from mothers with no risk factors, and even C-section does not eliminate the risk for neonatal Erb's palsy.
Interestingly, a higher rate of clavicular fractures have not shown an association with BPBP, but a notable association was found between BPBP and fracture of the middle third of the clavicle.

# Screening
As mentioned previously, the majority of Erb's palsy cases appear in children of mothers with no risk factors, for this reason, the condition is impossible to predict and becomes a challenge for the entire team to reduce this risk to the minimum. However, prenatal care can help us know when a vaginal delivery may be complicated:
- Pelvic measurements. Will inform us if the maternal pelvis is narrow and its form (gynaecoid, anthropoid, platypelloid, android), which could complicate the delivery.
- Serum glucose measurements. Will inform us of maternal diabetes, which is directly associated with macrosomic children.
- Prenatal ultrasound. Will inform us of the fetal presentation and the approximate fetal weight.
Once the child is delivered, several findings that can make us suspect an Erb's palsy:
- Negative ipsilateral Moro reflex, and positive palmar grasp reflex.
- Muscle tone and movement scale.

# Natural History, Complications, and Prognosis
Prognosis is generally good; If left untreated, <25% of neonates Erb's palsy may progress to develop permanent disability and impairment, while the rest will recover spontaneously after a month, depending on the severity of the injury (close to 100% of neuropraxias).
Denervated muscles become irreversibly injured after 18 to 24 months, and these time-sensitive changes become the basis for early management.
Several scales have been developed to predict the prognosis in Erb's palsy: Toronto test score, active movement scale, mallet scale, and Toddler Arm Use Test
Common long term complications of Erb's palsy include:
- Reduced strength and stamina
- Irregular joints function
- Muscular atrophy
- Abnormal bone growth
- Osteoarthritis
- Limb length discrepancy
- Impaired balance, and coordination

# Diagnosis

## Diagnostic Study of Choice
The diagnosis of Erb's palsy is made clinically, but several studies may help to confirm it or rule out other conditions, such as ultrasound, MRI, electromyography (EMG), x-rays, and CT.

## History
The classic history of a newborn with Erb's palsy is a macrosomic baby born from a diabetic mother with prolonged vaginal delivery, which presents with shoulder dystocia.

## Physical Examination
- Patients with Erb's palsy usually appear on physical examination with the affected arm held limply adducted, internally rotated, and pronated with an outward direction of the palm, wrist flexed and clung fingers (waiter's tip position). The patient is unable to abduct or externally rotate the shoulder. Sensory involvement is usually confined to the shoulder and along the distribution of the musculocutaneous nerve. Biceps, brachioradialis, and Moro reflexes are absent with hand movement and palmar grasp present (differentiating factor from Klumpke palsy).  The sensation is impaired in the skin of the shoulder, anterolateral forearm, index and thumb fingers.  Ocassionaly, there can be phrenic nerve palsy leading to hemidiaphragmatic paralysis.
- In prolonged Erb's palsies, atrophy of the deltoid, biceps, and brachialis muscles can be observed.
- Ultrasound is many times the initial study when there is a suspected glenohumeral dysplasia. The advantages of this study is that it doesn't produce any ionizing radiation, and can be performed without sedation.

## Electrophysiology/EMG
Electrophysiology studies are probably the single most important imaging study for Erb's palsy, and an important tool when making surgical and therapeutic decisions. EMG can detect the presence of fibrillation potentials indicate denervation. Among the applications for these kinds of studies are that they help categorize the localization, extent, and the type of lesion (preganglionic/ postganglionic), postoperative monitoring, the status of individual muscles (denervated, reinnervating, etc), and can give you a compound motor action potential (CMAP) diagnosis that will dictate the need of surgery in crucial period, before 3 months of age. EMG fails to describe the etiology and prognosis of Erb's palsy, but when used early, can distinguish between intrauterine cases of palsy from those aquiered during delivery.

## X-ray
Help to rule out shoulder dislocations, clavicular, humeral, and rib fractures, as well as accesory cervical ribs, and raised diaphragm (phrenic nerve injury).

## CT scan
- CT, in addition to evaluating bone features with greater precision than X-rays, may detect pseudomeningoceles, which could be a sign of nerve root avulsions, also evaluates the status of the nerve elements when an exploration or reconstructive surgery is planned.
- CT myelography used to be the gold standard for evaluation of nerve roots avulsion in adults but now is rarely used; It utilizes intrathecal injection of water-soluble iodinated contrast material.

## MRI
- MRI can detect the same findings as CT scans, with greater sensitivity for soft tissues.
- MR myelography is also used in the evaluation of Erb's palsy, but unlike CT myelography, it doesn't need constrast material, instead, uses the intrinsic contrast generated between the nerve roots and the surrounding CSF.

# Treatment

## Medical Therapy
There is no consensus on the appropriate treatment for Erb's palsy since this will depend on the severity of the affection, age of the patient, and prognosis. Treatment is often multidisciplinary and aimed to be as conservative as possible.
- Immobilization and splinting. It is commonly used during the first week from injury to avoid flexion contractures.
- Electrostimulation. Its use is still controversial.
- Hydrotherapy. It is a useful method of physical therapy, due to its anti-gravity properties, facilitates muscle relaxation, and range of motion; at the same time, it increases strength and muscle build-up due to water resistance.
- Physiotherapy: It can be done in combination with hydrotherapy or alone. Consist of passive and active range of motion, strengthening, and stretching exercises.
- Occupational therapy. It is usually required for adult patients with long-term damage to help them deal with daily-living activities (eating, tying shoes, playing, drawing).

## Surgery
Surgery is not the first-line treatment option for patients with Erb's palsy. Surgery is usually reserved for patients with no functional recovery from physical therapy and will depend on the time from damage, the cervical roots involved, and the patients age.
In infants, surgical intervention is indicated if the motor function does not improve after 3 months of age. After 20 to 24 months of denervation, exists a loss of neuro-muscular endplates, which makes the timing for surgery a crucial point.
Surgical intervention includes nerve decompression, nerve repairs, and graft implantation, with great chances of success.
One of the surgical procedures done for persistent cases is Hoffer-procedure, which has been shown to improve functional outcomes when operated before age 2.5 years.
Secondary reconstruction procedures have been realized in patients as a last resource to gain partial functionality. These include:
- Pectoralis major release to improve passive range of motion
- Tendon transfers for decreased active external rotation
- Trapezius transfer to stabilise shoulder
- Fractional release of the pronator teres and the lacertus fibrosis to improve passive supination
- Shoulder and wrist arthrodesis to improve posture

## Primary Prevention
Effective measures for the primary prevention of Erb's palsy include prenatal screening to detect fetal, or maternal risk factors, and close management of mothers with diabetes and obesity.

## Secondary Prevention
Effective measures for the secondary prevention of Erb's palsy include the application of shoulder dystocia maneuvers during labor (placement of mother in McRobert's position), and once detected a brachial plexus palsy, prompt medical or surgical management when necessary.

## Tertiary Prevention
Effective measures for the primary prevention of Erb's palsy aims to improve functionality in patients with brachial paralysis through physiotherapy and occupational therapy.