Median Nerve Palsy

Nerve supply

• Motor
  • Anterior forearm compartment
    • Superficial
      • Pronator teres
      • Flexor carpi radialis
      • Palmaris longus
      • Flexor digitorum superficialis (proximal interphalangeal joint flexion)
    • Deep
      • Flexor pollicis longus
      • Pronator quadratus
      • Medial half of flexor digitorum profundus (distal interphalangeal joint flexion)
  • Hand
    • Lateral two lumbricals
    • Opponens pollicis
    • Abductor pollicis brevis
    • Flexor pollicis brevis
• Sensory
  • Palmar aspect of lateral three and a half digits
  • Palmar sensation (palmar cutaneous branch, proximal to wrist crease – not in carpal tunnel)

Physical signs

• Inspection
  • Wasting of the thenar eminence
  • Hand of benediction (if injured at the elbow, seen when asked to make a fist) – paralysis of FDS, lateral FDP and the lateral two lumbricals
• Power
  • Opponens pollicis
    • “Make an OK sign”
  • Flexor pollicis
    • “Push up against my thumb”
  • Abductor pollicis
    • “Push in against my thumb”
  • Lateral two lumbricals (flexion MCPJs and extension of IPJs)
• Sensation
  • Numbness over lateral three and a half digits
  • Palm affected in lesions proximal to the wrist
• Other tests
  • Tinnel’s test (percussion of the wrist distal to the wrist crease with the wrist extended) – tingling

Causes

• Compression neuropathy
  • Carpal tunnel syndrome (sparing of thenar sensation) – see “Approach to Hand Pain”
  • Pronator teres syndrome
  • Anterior interosseous neuropathy (rare, only motor components, particularly opponens pollicis)
• Trauma
  • Supracondylar humeral fracture
• Vasculitis (mononeuritis), e.g. ANCA-associated vasculitides
• Infections (HSV, Lyme disease)

 Investigations

• Nerve conduction studies to confirm diagnosis and assess severity
• Consider EMG of thenar eminence
  • Electrically silent
  • Recent denervation: fibrillation potentials
• Consider full blood count (anaemia of chronic disease)
• Renal function (secondary CTS)
• Fasting plasma glucose, HbA1c (secondary CTS)
• Consider autoimmune profile
  • Anti-nuclear antibody
  • Rheumatoid factor, anti-cyclic citrullinated peptide (RA, secondary CTS)
  • Anti-neutrophil cytoplasmic antibody
  • Extractible nuclear antigens
• Consider anterior pituitary hormone screen
  • Insulin-like growth factor 1 (acromegaly, secondary CTS)
  • Thyroid function tests (hypothyroidism, secondary CTS)
• Consider Borrelia burgdoferi serology if Lyme disease suspected

Management

• Multidisciplinary team approach
• Physiotherapy and occupational therapy to regain function
  • Wrist splinting in 30° extension
• Local steroid injections
• Carpal tunnel release surgery