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 the sharp and dull sides of the neurotip at random. Ask the patient if they percieve the stimulus as sharp or dull.Spinothalamic tract
- Vibration - with the patient's eyes closed, place a vibrating 128hz tuning fork over the interphalangeal 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.Dorsal column - medial lemniscus pathway
- Proprioception - ask the patient to observe as you demonstrate upward and downward movement of the great toe. With their eyes closed, slowly move the joint over one to two seconds to the upward or downward position. Ask the patient to report whether the toe has been moved up or down. Repeat several times, and then repeat on the other side.Dorsal colun - medial lemniscus pathway
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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