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Can anyone explain to me the mechanism by which a tuning fork/vibration actually tests the sensory nerves? Is it more or less sensitive than the monofilament or just testing differently? I recently had a Pt with MS who GP referred for neurol tests- she felt monofilament at all sites tested, but not the tuning fork at all.......conclusions are???

 

Tuning fork measures Vibration, usually one of the earlier sensations to be lost as vibration is carried on very small nerve fibres. Monofilament measures cutaneuos perception threshold. So they measure different things. Monofilaments though have been validated over and over again to indicate that a person with diabetes who does not detect the 10g filamant (at 2 or more sites tesyed on a foot) is at a 7-10 times increased risk of developing a foot ulcer than someone who does.

 

Thanks - the first sentance answers my question, as I didn't realise that vibration sensation is usually lost earlier...so I guess that has implications in balance/falls etc. Thanks! (Now I just need to refresh my knowledge (or lack!) of MS!)

 

I thought the nerve fibres responsible for vibration were large.

 

Vibration sensation is not necessarily lost first. As in any CNS injury or disease, the location of the lesion dictates what is affected. While there are similarities between cases of MS, it is unlikely that two people will have the same symptoms. One of the hallmarks of the disease is it's unpredictability.

I have MS and have lost sensation in the distal half of both feet. In some places it's deep sensation, in others it's light / surface sensation that has been lost. Proprioception is generally spared. Vibration sense is good, especially over bony prominences. And it varies from day to day, week to week.

Challenging, ocassionally frustrating, but to the degree that I can step back and look at the neurology, it's fascinating.

While you're reading, take a look:
http://www.nationalmssociety.org/site/TR?px=1889879&pg=personal&fr_id=5870

Mark

 

Just to clarify, it depends on the condition. For eg, in diabetic neuropathy, vibration is lost first.

 

To further clarify, it also depends on whether condition is affecting the CNS or the peripheral NS. Any change in sensation bears deeper investigation though. It's all connected (or disconnected, as the case may be.)