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Upper Limb Neuro

Power Assessment

February 15th, 2021


Power assessment is a key part of the motor examination, and can be used to identify focal or global weakness.
  • How to Perform

  • Ask the patient to move their fingers, thumb, wrist, elbow and shoulder through each movement.
Start by asking the patient to move against resistance (5 / 4). If the patient cannot move against resistance, ask them to move the joint against gravity (3). If they still cannot move the joint, eliminate gravity (2). In the absence of signficant movement of the joint look for flicker movement (1 / 0). Grade as appropriate, comparing both sides.
  • Grading of Power

  • 0: no movement
  • 1: flicker of movement
  • 2 : movement without gravity
  • 3: movement against gravity
  • 4: against weak resistance
  • 5: normal power
  • Causes of Weakness

  • Upper Motor Neuron

  • Brain lesion - ischaemia, haemorrhage, tumour, trauma, encephalitis, vasculitis, demyelination
  • Spinal cord lesion - infarct, haemorrhage, abscess, transverse myelitis
  • Lower Motor Neuron

  • Nerve root pathology - trauma, radiculopathy, neoplasm
  • Brachial plexopathy - trauma, tumour, brachial neuritis
  • Focal peripheral nerve pathology - trauma, entrapment, focal ischaemia, sarcoidosis, tumour
  • Mononeuritis multiplex - vasculitis, diabetic neuropathy, Lyme disease, leprosy, paraneoplastic, amyloidosis, sarcoidosis
  • Peripheral polyneuropathy - diabetic neuropathy, hypothyroidism, B12 deficiency, alcohol, paraneoplastic, Guillain-Barre, CIDP, Charcot-Marie-Tooth
  • Other

  • Neuromuscular pathology - myasthenia gravis, Lambert Eaton myaesthenic syndrome
  • Muscular pathology - muscular dystrophy, inflammatory myositis, paraneoplastic, thyroid disease, Cushing's, statins, sarcoidosis
  • Poor compliance with examination
  • Interpretation

  • Weakness affecting an entire limb or entire side - likely due to central pathology
  • Weakness affecting a single myotome  - likely due to spinal nerve root pathology
  • Weakness affecting a single peripheral nerve distribution - likely due to a focal peripheral nerve palsy
  • Weakness affecting multiple peripheral nerve distributions - potentially due to a brachial plexus lesion, or mononeuritis multiplex
  • Generalised weakness - suggests a polyneuropathy, neuromuscular pathology or myopathy

Upper Limb Myotomes

Shoulder abduction: axillary nerve (C5)Lateral deltoid, supraspinatus
Shoulder adduction: C6/C7/C8Pectoralis major, trapezius, teres major
Elbow flexion: musculocutaneous nerve (C5/C6)Biceps, brachoradialis
Elbow extension: radial nerve (C7)Triceps
Wrist flexion: radial nerve (C6/C7)Flexor carpi radialis & ulnaris
Wrist extension: radial nerve (C6/C7)Extensor carpi radialis & ulnaris
Wrist ulnar deviation: ulnar / radial nerves (C8)Flexor & extensor carpi ulnaris
Wrist radial deviation: radial / median nerves (C6/C7)Flexor & extensor carpi radialis
Phalange flexion: median nerve (C8)Flexor digitorum profundus & superficialis
Phalange extension: radial nerve (C7)Extensor digitorum
Phalange abduction: T1

The Motor Pathway

Upper Motor Nucleus
Primary motor cortex (precentral gyrus)
Central Pathway
Corticobulbar tract
(via cerebral peduncle)
Medullary Pyramids
Spinal Pathway
Lateral corticospinal tract
Lower Motor Nucleus
Ventral horn at the level of entry into the spinal cord
Neuromuscular Junction
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