Starting with a patient with probable Fisher syndrome, we discuss the various ways to electrically image the brainstem. Here is what we came up with (there are other tests for research purposes, but this is what we routinely can or should be able to do):
- Blink reflex
- Calorics or rotating chair, or better: quantitative Halmagyi
- VEMPs (we don’t do these, but they are easy to perform)
- of course: long tracts (SEP, MEP)
We plough throught the neuroanatomy of the blink reflex, it’s technical aspects and various lesions with their typical and atypical blink reflex pathologies.
The blink reflex used to be an issue in the seventies and eighties, then with MRI we rediscovered it’s localizing potential (as opposed to – say – the masseter reflex). But it is really only useful if the MRI is negative, i.e., in those MRI-negative strokes and inflammatory lesions as well as cranial neuropathies. In the case of the latter I have to admit that a proper examination is often more effective than a good blink reflex.
As for references I turn to my beloved book on neurophysiology, which is now available in a new edition.