Are there any tools that we can use to differentiate Bells palsy from a CVA to prevent us from an unnecessary stroke bypass?
Excellent question. Central (CNS, e.g. stroke) causes of Facial Nerve (Cranial Nerve VII) palsy spares the forehead (the patient can still wrinkle their forehead) however, peripheral (outside of the CNS) causes of Facial Nerve Palsy (such as Bells palsy) do not: the patient is unable to use their frontalis muscle to wrinkle their forehead. Note however, that Bells Palsy ONLY affects the Facial Nerve. Therefore, if there are other neurologic deficits, other causes, including stroke should be entertained.
Unfortunately, it is sometimes difficult to confidently state that a particular neurologic presentation is due to a cranial nerve palsy (e.g. Bells palsy) versus a more sinister cause (e.g. stroke). If there is any doubt whatsoever, the safest option would be transport to a stroke center.