Overview
How to Assess
- Light touch - Ask the patient to close their eyes. Using a cotton ball or microfilament, gently touch each dermatome / nerve distribution and ask the patient if they can feel the stimulus. Compare sides and proximally / distally.Spinothalamic tract & dorsal column - medial lemniscus pathway
- Pain - demonstrate a sharp stimulus by touching the patient lightly on the chest with a neurotip. Ask the patient to close their eyes, and test each dermatome / nerve distribution alternating between sharp and dull sides of the neurotip. Ask the patient if they feel sharpness or dullness.Free nerve endings → spinothalamic pathway → sensory cortex
- Vibration - with the patient's eyes closed, place a vibrating 128hz tuning fork over the IP joint of the great toe. Ask the patient to describe the sensation. If they can feel it vibrating, progressively diminish the vibration until they cannot feel it. If they cannot feel it vibrating, test on the medial / lateral malleolus and then the tibial tuberosity.Pacinian corpuscles → dorsal column → medial lemniscus → sensory cortex
- Proprioception - ask the patient to observe as you move the great toe up and down, holding either side of the IP joint. With their eyes closed, slowly move the joint up or down. Ask the patient whether the toe has moved up or down. Repeat several times, and repeat on the other side.Neuromuscular spindles → dorsal column → medial lemniscus → sensory cortex
Interpretation
- Central - tends to involve an entire upper and / or lower limbIschaemia, SAH / ICH, tumour, trauma, encephalitis, vasculitis, MS, ADEM, PML, sarcoidosis
- Axon - Begins distally and migrates proximally → 'glove and stocking' distributionDiabetes, hypothyroidism, B12 / folate deficiency, alcoholism, connective tissue disease, amyloid / sarcoidosis, toxins
- Myelin sheath (demyelination) - impaired proprioception and vibration sensation with intact pain sensationGuillain-Barré syndrome, CIDP, Charcot-Marie-Tooth
- Nerve root - in the distribution of a single dermatomeTrauma, radiculopathy, neoplasm
- Peripheral nerve - in the distribution of a peripheral nerveTrauma, entrapment, focal ischaemia, neoplasia, shingles, nerve block
- Skin receptors - localised to an area not in keeping with a dermatomal or peripheral nerve patternTrauma, local anaesthesia, full thickness burns
Peripheral Neuropathy
Look For
- Loss of / altered sensation in the hands and / or feet, in a 'glove and stocking distribution.
Causes of Peripheral Neuropathy
- Endocrine - diabetes, hypothyroidism, acromegaly
- Deficiency - B12 / folate deficiency, alcoholism
- Connective tissue disease - rheumatoid arthritis, polyarteritis nodosa, SLE
- Deposition - amyloidosis, sarcoidosis
- Infection - AIDS, lyme disease
- Toxins - arsenic, mercury, organic phosphates, carbon monoxide
- Critical illness polyneuropathy
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