Median nerve

Home, Search, Index, Links, Pathology, Molecules, Syndromes,
Muscle, NMJ, Nerve, Spinal, Ataxia, Antibody & Biopsy, Patient Info

MEDIAN NERVE

Anatomy
Local lesion syndromes
Anterior interosseus
Carpal tunnel
Ligament of Struthers
Palmar cutaneous
Pronator syndrome
Thenar motor

Median nerve: Anatomy

Formed by
- C5 to C7 roots from lateral cord of brachial plexus
- C8 and T1 roots from medial cord of brachial plexus
Branches
- Forearm: Muscular branches
  - Pronator teres
  - Flexor carpi radialis
  - Flexor carpi sublimis
- Anterior interosseus (motor)
  - Flexor pollicis longus
  - Flexor digitorum profundus to 2nd & 3rd fingers
  - Pronator quadratus
  - External link: Anatomy & Exam
- Palmar cutaneous
  - Sensory distribution: Skin over thenar eminence
  - Branch arises proximal to carpal tunnel
- Terminal motor
  - Abductor pollicis brevis
  - Opponens pollicis
  - Lumbricals: 1st & 2nd
  - ± Flexor pollicis brevis: Also innervated by ulnar nerve
- Terminal sensory
  - Sensory to palmar surface of thumb, 2nd, 3rd & lateral 1/2 of 4th finger
Anomalies & Variant branches
- Martin-Gruber anastomosis (10% to 44% of normals)
  - Branches from median to ulnar nerve in forearm: 2 patterns
    - Median nerve in proximal forearm: To ulnar nerve in middle to distal third of forearm
    - From anterior interosseus nerve: To ulnar nerve
    - Often bilateral: 60% to 70%
  - Variant branches may innervate
    - 1st dorsal interosseus: Most common
      - Median stimulation at Elbow produces 1st DI response
    - Thenar muscles: Adductor pollicis; Flexor pollicis brevis
      - Median stimulation at Elbow produces greater thenar response than from Wrist
      - May complicate: Carpal tunnel studies
    - Hypothenar muscles (Abductor digiti minimi)
      - Median stimulation at Elbow produces hypothenar response
      - May mimic: Ulnar conduction block
  - NCV features
    - Larger thenar CMAP from median stimulation at elbow than wrist
    - Initial positive CMAP from stimulation at elbow
    - Median mononeuropathy: Median forearm conduction is artificially fast
- Riche-Cannieu anastomosis
  - Connections between deep ulnar & median nerves in hand
  - Frequency: 77% of hands
  - May cause
    - Median innervation of normally ulnar innervated muscles
    - Ulnar innervation of normally median innervated muscles
    - Rarely: May produce all ulnar innervated hand
- Medial to Radial nerve anastomosis
  - Radial nerve innervates: Abductor pollicis brevis

Median nerve: Lesions

Gowers
Normal hand Thumb is perpendicular to plane of palm	Median nerve lesions Thumb is externally rotated into plane of palm. Thenar eminence is wasted.

High Median nerve lesions
- General
  - Hand posture: Thumb, index & middle fingers remain extended with attempted grip
  - Pain: Present in region of entrapment
- Axilla
  - Crutch compression
  - Missle injury
  - Anterior shoulder dislocation
  - Lipoma or other neoplasm
  - Medial brachial fascial compartment syndrome
- Upper arm
  - Stab wounds: ± Brachial artery injury
  - Sleep palsy: Near pectoralis major tendon
  - Tourniquets
  - Fracture: Humerus shaft
- Elbow
  - Supracondylar spurs & ligaments (Ligament of Struthers)
  - Fracture
    - Humerus supracondylar: Children; Anterior interosseus distribution
    - Medial epicondylar
  - Elbow dislocation
  - Injection injury
  - Pronator syndrome
- Supracondylar spurs & ligaments (Ligament of Struthers)
  - Median nerve anatomy
    - Entrapped by band from medial epicondyle to supracondylar spur on distal, medial humerus
    - Spur occurs in 1% of population
      - May be associated with high origin of: Pronator teres & Anterior interosseus nerve
      - Under ligament: Median nerve; Brachial artery
      - Over ligament: Ulnar artery
  - Pain: Volar forearm
  - Paresthesias: Median-innervated digits
  - Weakness: Pronator teres; Other median muscles
  - Sensory loss: Mild; Median distribution, including thenar eminence
  - Exacerbated by: Supination of arm + Extension of elbow
    - Radial pulse may also be reduced
- Pronator teres syndrome (Pronator syndrome)
  - Pain
    - Locations: Volar forearm; Proximal arm
    - Exacerbated by
      - Repeated or resisted pronation
      - Resistance to isolated flexion of PIP joint of long and ring fingers
    - Associated with: Paresthesias in median innervated fingers
  - Pronator teres muscle
    - May be enlarged or firm
    - Tinel's sign over site of entrapment
  - Weakness: Mild or None
    - May be present in APB or Flexor pollicis longus
  - Sensory loss
    - Objective: Mild or none
    - Subjective: Sense of numbness
  - Laboratory
    - EMG: Denervation in median-innervated muscles (70%)
    - NCV: Abnormal median sensory responses (65%)
  - Treatment: Surgical release produces improvement in 50%
Anterior interosseus syndrome
- Nosology: Kiloh–Nevin syndrome
- Anatomy: Arises from median nerve, 5 cm above medial epicondyle
- Causes
  - Most common: Proximal median fascicular lesion
  - Fracture: Radius midshaft
  - Excessive exercise
  - Idiopathic
  - Direct trauma: Stab wound; Venipuncture
  - Anatomic anomalies
    - Vessel: Radial artery in mid forearm; Ulnar artery thrombosis
    - Muscle: Deep palmar compartment; From aberrant accessory muscles
      - Gantzer's muscle: Accessory head to Flexor pollicis longis
      - Origin of: Palmaris profundis; Flexor digitorum sublimis; Flexor carpi radialis
    - Fibrous bands: Origin of Flexor Digitorum Sublimis
    - Course of nerve deep to pronator teres
  - Brachial neuritis (Neuralgic Amyotrophy)
- Muscles innervated
  - Flexor pollicis longus
  - Flexor digitorum profundus to 2nd & 3rd fingers: FDP to other fingers innervated by ulnar nerve
  - Pronator quadratus
  - Martin-Gruber anastomosis: Intrinsic hand muscles weak
  - External link: Anatomy & Exam
- Weakness
  - Flexion of distal joint of thumb & 1st finger
  - Pronation of forearm with elbow flexed
  - Martin-Gruber anastomosis: Intrinsic hand muscles weak
- Sensory
  - Loss: None; No cutaneous innervation
  - Pain: Some patients; Variable
- Muscle MRI (T2W fat-saturated images)
  - High signal in Anterior Interosseus innervated muscles: Especially in pronator quadratus
- Similar Weakness also seen with
  - Brachial neuritis: Lateral cord lesion
  - Supracondylar fractures
  - AIN Fascicular syndrome ³
    - Location: Proximal median nerve lesions
      - 15 cm proximal to humero-radial joint
      - Lesions may be monofocal or multifocal
    - Diagnostic test: T2 magnetic resonance neurography (MRN)
    - Frequency: Most patients with AIN syndromes
    - Cause: Neuroma, Torsion, or other
  - Tendon rupture: Flexor pollicis longus & Flexor digitorum profundus in rheumatoid arthritis
- Course: Spontaneous recovery in > 50%
Median neuropathy in forearm
- Bleeding into flexor compartment
  - Hemophiliacs; Anticoagulants; Brachial artery puncture
- A-V fistula for dialysis: Pain common; Onset days to weeks after surgery

Carpal tunnel syndrome

Epidemiology
- Female: Male:: 3:1
- Age peak: 40 to 60 years
- Dominant hand
  - Often affected 1st & more severely
  - More common in idiopathic cases
- Commonly becomes bilateral
- Rare in absence of pain
Causes
- Idiopathic: ? Related to
  - Congenital smallness of carpal tunnel
  - Hand activity: Repetitive; Amount
  - More common in dominant hand
- Occupational: Vibrating tool use
- Anatomic: Reduced space in carpal tunnel
  - Tenosynovitis: Rheumatoid arthritis or suppurative
  - Bone: Fracture; Osteophyte; Dislocation; Exostosis
  - Mass: Ganglion; Gouty tophi; Hematoma
  - Anomalous muscles
    - Flexor digitorum sublimis
    - Palmaris longus
  - Median artery, Persistent
  - Congenital smallness of carpal tunnel
  - Neoplasms: Ganglia; Hemangioma; Lipoma;
    Neurofibroma; Schwannoma
- Susceptibility of nerve to pressure
  - Hereditary
    - PMP-22
      - Hereditary Liability to Pressure Palsies
      - Point mutations
    - SH3TC2 heterozygote
    - SPG31: REEP1
  - Systemic disease
    - Diabetic Neuropathy
    - Renal failure
    - Leprosy: Lesion proximal to carpal tunnel
  - Polyneuropathies
- Systemic disorders
  - Pregnancy: Often resolves after delivery
  - Endocrine
    - Hypothyroidism
      - Mucopolysaccharide deposits under flexor retinaculum
    - Acromegaly: Median nerve edema
  - Multiple myeloma
  - Amyloidosis
  - Obesity
  - Osteochondritis dissecans
  - Spasticity
  - Edema
  - Immune disorders: Rheumatoid arthritis; Sarcoid
  - Infection: Histoplasmosis; Lyme; Septic arthritis; Tubercuolsis
- Hereditary
  - CTS Risk factors
    - Biglycan (BGN)
    - Aggrecan (ACAN)
    - COL5A1
    - IL6R
    - NGF-β: Heterozygotes ⁵
  - Carpal tunnel syndrome ¹
    - Anatomy
      - Wrist X-rays: Narrow carpal tunnel
      - Thick transverse carpal ligament
    - Epidemiology
      - 1 family
      - All female
      - Lethal in males
    - Genetics
      - X-linked Dominant
    - Clinical
      - Onset
        
        Age: < 2nd decade
        
        Pain in lateral fingers
      - Bilateral
  - Recessive: Childhood onset
  - CTS1 : TTR, Dominant
  - CTS2: COMP, Dominant
  - Mucopolysaccharidosis: Scheie
  - Mucolipidosis
  - HNPP
  - SH3TC2 heterozygote
  - NGFB carriers
  - Klippel-Trenaunay-Weber
- Childhood
- Acute
  - Wrist fractures (Colles), dislocations (lunate bone, hyperextension), hematomas
  - Pyogenic infections: tenosynovitis
  - Rhematoid arthritis: Acute exacerbation
  - Excessive unaccustomed manual work
Clinical features
- Clinical
  - Pain
    - Episodic
    - Temporal: Worse at night initially; Later during day also
    - Location: Arm, forearm, wrist, hand & fingers
    - Repetitive or sustained activity: Exacerbates pain
    - Flick sign: Nocturnal awakening with pain relieved by vigorous hand shaking
  - Paresthesias & Sensory loss
    - Palmar thumb, 2nd, 3rd & medial 4th fingers
    - Finger tips
    - Nocturnal: Common
    - Normal: Thenar eminence
  - Weakness: After sensory loss
    - Abductor pollicis brevis (APB): Most common
    - Opponens pollicis
  - Provocative tests
    - Phalen maneuver
      - Wrist held passively flexed
      - Symptoms in 30 to 120 sec
      - Most common: Paresthesias in index or middle finger
    - Tinel sign
      - Tapping over median nerve at wrist
      - Produces paresthesias
      - May be false positive
  - Treatment
    - Splinting
      - Set to reduce pressure in carpal tunnel
      - Wrist angle: Neutral (Close to 0°)
    - Corticosteroid injections
    - Surgical decompression: Complete section of transverse carpal ligament
      - Primary treatment in acute carpal tunnel syndrome
      - Avoid in pregnancy
Laboratory
- Electrodiagnostic
  - Slow sensory conduction across transverse carpal ligament: Most sensitive
  - Later changes: Long motor latency; Low CMAP; Denervation in APB
- Ultrasound: Nerve properties
  - Hypoechogenicity
  - Vascularity: Increased
  - Mobility: Decreased
  - Cross-sectional area: Increased
  - Flexor retinaculum: Increased bowing
- Systemic work-up: Thyroid; Blood sugar; Sed rate; CBC
External link: Ortho-u

From: C Zaidman
Carpal tunnel syndrome: Ultrasound images of Median Nerves
Cross-sectional area: Increased
Echogenicity: Reduced

Thenar Motor Neuropathy ²
- Definition
  - Mononeuropathy of median motor branch supplying thenar eminence muscles
- Epidemiology
  - Frequency: 0.3% of median neuropathies
  - Males more common
- Causes
  - Wounds to the palm
  - Iatrogenic damage after surgery: Often for carpal tunnel syndrome
  - Masses, especially ganglion cysts
  - Occupational: Vineyard & Metal workers; Hand milkers; Office
  - Idiopathic
- Clinical
  - Weakness: Opposition & Abduction of thumb
  - Dominant hand
  - Hypotrophy or atrophy of thenar eminence
- Electrodiagnostic
  - Abductor Policis Brevis (APB) distal motor latency: Long
  - APB CMAP: Small amplitude
  - Median motor CV: Mildly slowed
  - EMG: Neurogenic APB
Palmar cutaneous neuropathy
- Causes
  - Transverse incisions at wrist for carpal tunnel surgery
  - Anomalous palmaris longus muscle
  - Ganglion from blunt trauma to wrist
  - May occur along with carpal tunnel syndrome
- Clinical
  - Numbness over thenar eminence
- Electrodiagnostic testing
  - SNAP from palmar cutaneous branch of median nerve

Carpal Tunnel Syndrome, Familial 2 (CTS2) ⁴

● Cartilage Oligomeric Matrix Protein (COMP)

; Chromosome 19p13.11; Dominant

Epidemiology: 2 families
Genetics
- Mutations: Missense; V66E (N-terminal Coiled coil domain), R718W (Also associated with MED)
- Allelic disorders
  - Multiple Epiphyseal Dysplasia (MED) & Myopathy
  - Epiphyseal dysplasia, multiple, 1 (EDM1) : TSP type III repeats or C-terminal globular domain mutations
  - Pseudoachondroplasia (PSACH) : TSP type III repeats or C-terminal globular domain mutations
- CTS1: TTR gene mutations
COMP protein
- Extracellular matrix protein
- Present at myotendinous junction
- Interacts with cell surface integrin receptors
- Suppresses apoptosis: Blocks activation of caspase-3
- Mutations associated with: Impaired COMP secretion & complex formation
Clinical
- Carpal tunnel syndrome ± MED
- Onset age: Mean 3rd decade; Range Teens to 5th decade
- Pain, Paresthesia & Numbness: Thumb, Index & Middle fingers
- Weakness & Atrophy: Thenar
- Trophic ulcers, Digital
- Transverse carpal ligaments & Flexor tendons: Severely enlarged
- Joint hypermobility: Some families
Laboratory
- Ligament pathology: Thick; Collagen Fragmentation & Edema

Return to Neuromuscular home page
Go to Innervation of upper extremity muscles

References
1. Acta Neurol Scand 2001;104:377-379
2. J Clin Neurophysiol 2010;27: 344–349
3. Neurology 2014;82:598–606
4. Nat Commun 2020;11:3642
5. Brain Commun 2020;2(2):fcaa085

6/7/2021

MEDIAN NERVE

Carpal Tunnel Syndrome, Familial 2 (CTS2) 4

Carpal Tunnel Syndrome, Familial 2 (CTS2) ⁴