"If all else fails, do a sensory examination" Dr Neil Archibald
There can be few more depressing experiences as an examiner than watching someone attempt a sensory examination. I’m sorry, but it is TRUE!
You don’t want to do it. We don’t want you to do it. The longer you spend on it the worse it gets and, to add insult to injury, it hardly ever adds anything.
If you have taken a (decent) history then this will usually suffice as the sensory examination.
Basically, you are looking for a particular pattern to emerge:
- glove and stocking – think peripheral neuropathy
- sensory level – think spinal lesion
- nerve distribution – think nerve lesion (I know, who said it was complicated)
- fancy sensory stuff – Brown-Séquard, anterior cord or pasterior cord
Beyond this, it is all just a bit vague.
In addition, you always do it at the end because:
- you might have found out what you need already (clonus, pattern of weakness, reflex changes etc.)
- you might run out of time and not have to do it at all
Here are my tips for sanity and success.
- don’t use cotton wool at all (if it can be avoided). If you have to, do it last.
- the blunt end of the neurotip is for … holding. If you start trying to do sharp vs dull then I am walking away
- remember that pin (pain) and temperature travel together (in small, slow peripheral fibres and then in the spinothalamic tracts)
- remember also that JPS and vibration travel together (in large, fast fibres and then in the dorsal columns)
These modalities therefore tell you something about the state of large and small peripheral sensory nerves and/or distinct spinal pathways.
Light touch goes up multiple pathways and so adds very little to the mix (hence is often not tested at all.
This video gives you a quick demonstration of how to do a sensory examination. Incidentally, the start of the video shows a lady with increased tone in both legs and the beginnings of a pyramidal pattern of weakness. From this, you can guess that this is a “central” lesion and, if the upper limbs are normal (and they are) you would be right to think about the spinal cord.
The sensory exam doesn’t tell you a whole lot more but, in this case, was quite interesting as it picked up preserved JPS/VS and damaged pin/temp. Assuming you are right about the spinal cord localisation, and armed with a bit of spinal anatomy, you can see how this might suggest the anterior cord is damaged (pin/temp and motor) and the posterior cord is spared (JPS/vibration).
This pattern is highly suggestive of anterior spinal artery occulsion (spinal stroke).