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Signs
 
 

Lower Motor Neuron Weakness

 
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Overview

  • Signs of Lower Motor Neuron Weakness

  • Muscle wasting
  • Fasciculations
  • Reduced tone
  • Reduced power
  • Hyporeflexia
  • Downgoing plantar reflex
  • Interpretation

  • 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
  • Causes of Lower Motor Neuron Weakness

  • Spinal Nerve Root Pathology

  • Spinal trauma
  • Radiculopathy
  • Tumour
  • Brachial Plexopathy

  • Brachial plexus trauma
  • Brachial neuritis
  • Radiation injury
  • Tumour
  • Focal Peripheral Nerve Pathology

  • Trauma
  • Nerve entrapment (e.g. carpal tunnel syndrome)
  • Focal ischaemia
  • Peripheral nerve tumour
  • Sarcoidosis
  • Mononeuritis Multiplex

  • Vasculitis - polyarteritis nodosa, EGPA, GPA, cryoglobulinaemia, SLE, rheumatoid arthritis, Sjogren’s syndrome, scleroderma, Behcet’s disease
  • Diabetes
  • Infection - Lyme disease, leprosy, HIV, hepatitis B / C
  • Malignancy - lymphoma, small cell lung cancer
  • Amyloidosis
  • Sarcoidosis
  • Peripheral Polyneuropathy

  • Endocrine / nutritional - diabetic neuropathy, hypothyroidism, B12 deficiency
  • Demyelination - Guillain-Barré syndrome, Chronic inflammatory demyelinating polyneuropathy (CIDP)
  • Vasculitis - rheumatoid arthritis, polyarteritis nodosa, SLE
  • Infection - lyme disease, HIV neuropathy, leprosy, polio
  • Paraneoplastic syndrome
  • Multifocal motor neuropathy with conduction block
  • Motor neurone disease
  • Charcot-Marie-Tooth
  • Sarcoidosis
  • Drugs - ethambutol, certain chemotherapy agents, amiodarone, lithium
  • Toxins - alcohol, heavy metals, organophosphates
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