Very few people get this bit right, and given that it is, after inspection, the earliest part of examination, you’re on a hiding to nothing from the get go.
Basically, tone is either normal or increased. Pay no attention to those that comment on reduced tone; if you are totally relaxed, you have the same tone as someone with a flaccid paralysis, so I would recommend concentrating on detecting an increase in tone.
There are two types of increased tone – spasticity and rigidity
They are very different and require subtly different approaches to pick them up.
This is the increase in tone one sees in patients with disorders of the basal ganglia – Parkinson’s disease, dystonia etc.
The increased tone is seen throughout the range of movements, regardless of whether the movement is slow or quick. That said, it is best examined for with very slow, gentle movements, especially at the finger joints and wrist.
Rigidity can be increased by getting the patient to perform a counter-activation task with the opposite arm – I usually ask folk to “paint a wall”.
Sometimes, this can really dramatically increase the rigidity – as useful tip for the bedside,clinic and the exam room.
Spasticity is often referred to as “velocity-dependent”, which basically means that if you want to pick it up, you need to make quick movements of the affected limb.
In the arm, this means grasping the hand of the patient, as if you were shaking hands, and quickly flicking the forearm from prone to supine. If spasticity is present, you will feel a brief “catch” in the movement as you rotate, before it releases to let the movement proceed.
We tend to call this a “pronator catch”, a “supinator catch” or just a “spastic catch”.
In the legs, you can roll the leg from side-to-side, like you are making a worm out of plastcine, and look to see if the foot wobbles loosely; it should. You can also quickly bring the leg up off the bed, by lifting behind the knee; the heel ideally stays on the bed, with the leg flexing, if tone is normal.
A word of warning; sometimes, it is tricky to relax, and so you can get a sense of spasticity for this reason. Just be careful. If there is true spasticity, you will find plenty of other abnormal signs to help you, before you have finished, so don’t jump to conclusions too early.
This is one of my favourite signs, and also one of the most important.
It just so happens that is is also just about the worst performed bit of the neurological assessment we see!
My advice is to examine for it when you do tone, rather than with reflexes. True, it is basically an ankle jerk gone haywire, but if there is sustained clonus on examination, then you will almost certainly find a pyramidal/upper motor neurone pattern of weakness in the legs, brisk reflexes and extensor plantars, so it is a great clue to have in the bag early doors.
Notice the cunning example of “how not to do clonus” first, and the difference doing it right makes. I am sad to say that the first technique is the one taught to medical students when they do not get their teaching from neurologists.