Firstly, you need to know the signs of cerebellar dysfunction. The whole battery is almost never present (see below), so you have to actually seek out most of them.
Ataxia is poorly coordinated movement. Not all ataxia is caused by cerebellar disorders, of course. Gait ataxia refers to a jerky, unsure gait, where the steps vary in size and the feet are usually widely separated. (In subtle cases, only heel-to-toe walking may be impaired: the patient duly falls to one side on cue.) Truncal ataxia is manifested by the patient having difficulty keeping his/her trunk upright, whether sitting or standing. It is usually most marked when the feet are close together. Limb ataxia is shown by limbs that are clumsy, discoordinated, and that have difficulty with rapidly alternating movements (a phenomenon unhelpfully known as dysdiadochokinesis).
An intention tremor is one of the classic hallmarks of cerebellar disease. The person's tremor only occurs when he/she is wanting to touch a stationary object, and subsides once it has been reached.
Dysarthria has many causes, but if it caused by cerebellar disease, it is slow and monotonous with syllables abnormally separated. It sounds strikingly like limb ataxia looks.
Nystagmus - refers, as always, to an abnormal 'to and fro' movement of the eyes.
Tone - Tone should technically be slightly reduced on the affected side, but this is usually pretty difficult to detect. The patient's reflexes are said to be 'pendular' (i.e. they muscle swings like a pendulum).
Once you've looked for these things (there are even more in textbooks, but this should be sufficient), I've always found it helpful to sort the signs into one of two broad syndromes:
- Lateral Cerebellar Syndrome - Caused by lesions of one of the cerebral hemispheres, these patients with limb ataxia, and a tendency to fall to the affected side. Common causes include tumours, abscesses, strokes, trauma and multiple sclerosis.
- Central Cerebellar Syndrome, and Pan-cerebellar Syndrome- Vermal lesions affect equilibrium and result in gait ataxia with little or no limb ataxia. Flocculonodular lobe lesions present in the same way, but additional symptoms include nystagmus and vertigo. Alternatively, pretty much all the cerebellar signs may be present; we can call this 'pan-cerebellar syndrome'. Whether 'central' or 'pan-cerebellar', the common causes are drugs (phenytoin, alcohol, others), infections (including post-infectious syndromes), paraneoplastic syndromes, hypothyroidism, familial ataxias (e.g. Friedreic's ataxia) and developmental abnormalities of the brain.
I know it's still a lot, but at least we've been able to narrow the huge list of possible cerebellar insults down to five or six common ones, depending on our clinical findings. It works for me, most of the time, but perhaps you have other ideas?