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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